A laser ablated graphene-based flexible self-powered pressure sensor for human gestures and finger pulse monitoring - Partha Sarati Das, Ashok Chhetry, Pukar Maharjan, M. Salauddin Rasel, Jae Yeong Park (Nano Research, 2019)

Flexible and Washable Poly(Ionic Liquid) Nanofibrous Membrane with Moisture Proof Pressure Sensing for Real-Life Wearable Electronics - Zehong Wang, Yang Si, Cunyi Zhao, Dan Yu, Wei Wang, Gang Sun (ACS Applied Materials & Interfaces, 2019)

High Sensitivity and Broad Range Flexible Pressure Sensor Using Multilayered Porous PDMS/AgNP Sponge - Shuai Zhao, Rong Zhu (Advanced Materials Technologies, 2019)
Abstract Flexible pressure sensors attract wide attentions in recent years for their significant applications in wearable electronics and health monitoring. It is strongly desired that a pressure sensor possesses both low detection limit and wide measuring capability, covering a broad pressure range from Pa to hundred kPa, to meet diverse demands in different applications. This paper proposes a novel flexible pressure sensor based on thermosensation, using a multilayered and graded‐porosity polydimethylsiloxane/silver nanoparticle sponge as piezo‐thermic transduction. The sensor exhibits a high sensitivity, a low detection limit of 4.1 Pa, and a wide measuring range up to 200 kPa, which leads to a high range‐to‐limit ratio of about 50 000. The pressure sensor is monolithically integrated with a temperature sensor and dissolves temperature‐compensation. The unique combination of properties makes it feasible to monitor various human signals from subtle wri st pulse to finger tapping pressure and foot stepping pressure by a single device, which shows competent capabilities for multifarious applications in wearable electronics and health monitoring.

Thermochromic and Piezocapacitive Flexible Sensor Array by Combining Composite Elastomer Dielectrics and Transparent Ionic Hydrogel Electrodes - Hemant Charaya, Thanh‐Giang La, Jana Rieger, Hyun‐Joong Chung (Advanced Materials Technologies, 2019)
Abstract Electronic skin (e‐skin) is an important building block to achieve human–machine interfaces, functional prostheses, and health monitoring devices. While high pressure and temperature sensitivity with visible indication are important for e‐skins, such multifunctionality often requires complex fabrication and integration processes, which hinders practical applications. Here, a simple solution is shown to fabricate a bimodal e‐skin sensor array that is capable of changing color as a response to a range of temperatures (26–40 °C) with an ability to sense finger tap (≈20 kPa pressure) as a pressure sensor. The bimodal functionality of thermochromic response and tactile sensing is achieved by judicial material selection of our custom‐developed elastomer composite containing thermochromic dye, which is sandwiched by tough and transparent stretchable electrodes of ion‐containing polyampholyte hydrogels. The e‐skin array is potentially promising for appl ications in internet‐of‐things and soft robotics.

Effect of the sintering technique on the ferroelectric and d33 piezoelectric coefficients of Bi0.5(Na0.84K0.16)0.5TiO3 ceramic - G. Hernandez-Cuevas, J. R. Leyva Mendoza, P. E. García-Casillas, C. A. Rodríguez González, J. F. Hernandez-Paz, G. Herrera-Pérez, L. Fuentes-Cobas, S. Díaz de la Torre, O. Raymond-Herrera, H. Camacho-Montes (Journal of Advanced Ceramics, 2019)

Effects of loading contact on electric-power generation of lead zirconate titanate piezoelectric ceramic plate - Mitsuhiro Okayasu, Tsukasa Ogawa (Journal of Advanced Ceramics, 2019)
Abstract To better understand the generation of electric power for piezoelectric PbZrTiO 3 (PZT) ceramic plate ( ϕ 25 mm), an attempt was made to investigate experimentally and numerically electricpower generation characteristics during cyclic bending under various loading fixtures ( ϕ 0– ϕ 20 mm), i.e., different contact areas. Increasing the load-contact area on the PZT ceramic leads to a nonlinear decrease in the generated voltage. Decreasing contact area basically enhances the generated voltage, although the voltage saturates during loading when the contact area is less than ϕ 5 mm. A similar voltage is generated for ϕ 0 and ϕ 5 mm, which is attributed to strain status (ratio of compressive and tensile strain) and material failure due to different stress distribution in the PZT ce ramic. On the basis of the obtained electric generation voltage, suitable loading conditions are clarified by loading with the ϕ 5 mm fixture, which generates a higher voltage and a longer lifetime of the PZT ceramic. From this approach, it is appeared that the area contact with the area ratio of 0.04 ( ϕ 5 mm/ ϕ 20 mm) is suitable to obtain the high efficiency of the electric voltage.

Grain size dependent physical properties in lead-free multifunctional piezoceramics: A case study of NBT-xST system - Xing Liu, Saidong Xue, Feifei Wang, Jiwei Zhai, Bo Shen (Acta Materialia, 2019)

Novel Lead-free biocompatible piezoelectric Hydroxyapatite (HA) – BCZT (Ba0.85Ca0.15Zr0.1Ti0.9O3) nanocrystal composites for bone regeneration - Chelli Sai Manohar, B Siva Kumar, Sai Pavan Prashanth Sadhu, Sai Krishna Srimadh, V Sai Muthukumar, S. Venketesh, K. B. R. Varma (Nanotechnology Reviews, 2019)
Abstract BCZT (Ba 0 . 85 Ca 0 . 15 Zr 0 .1Ti 0.9 O 3 ) is a recent class of lead-free ferroelectric material associated with high piezoelectric coefficient, making it suitable to inspire hydroxyapatite (HA)-BCZT ceramics for bone materials. Nano-crystalline hydroxyapatite (HA) synthesized using the hydrothermal route was characterized via FT-IR, Raman spectroscopy, X-ray powder diffraction (XRD), and Scanning Electron Microscopy (SEM). We also rationalized its formation as a function of operating conditions such as dwell time and temperature in this route. The nano-crystalline BCZT powder was synthesized via a sol-gel technique and its structural and morphological characterization were carried out using Raman Spectroscopy, XRD and Transmission Electron Microscopy (TEM). These investigations facilitated the optimization of HA-BCZT compositions and their electrical poling conditions to achieve enhanced piezoelectric effect. The composites (HA-BCZT) sintered at 1350 ∘ C exhibited promising piezoelectric properties. We report the enhanced piezoelectric coefficient (d 33 ) of 7±1 pC/N for 50% HA-BCZT which is significant as compared to that reported in the literature for ~98% BT (barium titanate) -HA composites. We highlight the role of Simulated Body Fluid (SBF) on the intriguing phase-change of Tricalcium Phosphate (TCP) obtained at this sintering temperature, to hydroxyapatite for its essential contribution to promote bone growth. We theoretically support the confirmed in vitro biocompatibility of these composites. Graphical abstract : Novel lead-free biocompatible piezoelectric HA-BCZT nanocrystal composites for accelerated Bone regeneration

Phase‐Field Study of Electromechanical Coupling in Lead‐Free Relaxor/Ferroelectric‐Layered Composites - Shuai Wang, Azatuhi Ayrikyan, Haibo Zhang, Kyle G. Webber, Bai‐Xiang Xu (Advanced Electronic Materials, 2019)
The interface coupling effect of multilayer lead‐free ceramic/ceramic relaxor/ferroelectric composites is studied by finite element–based phase‐field simulations. The macroscopic electromechanical behavior of such composite systems is influenced by both polarization and strain coupling through the electrical and mechanical interaction of connected layers. Separating such interconnected phenomena is difficult experimentally. Here, we direct investigate different coupling effect by introducing soft and charge interphase layers in the serial‐type layer composite model. The large strain response of the composite results from the electric field–induced nonpolar–polar phase transition of the relaxor constituent. A new relaxor phase‐field model is first developed to reproduce this phase transition and parameterized by fitting the measured hysteresis loops. It is then directly compared to the experimental results of the serial‐type composite composed of 0.91Bi 1/2 Na 1/2 TiO 3 –0.06BaTiO 3 –0.03AgNbO 3 and 0.93Bi 1/2 Na 1/2 TiO 3 –0.07BaTiO 3 . Results show that the lateral strain coupling in the serial layer contributes considerably to the large signal piezoelectric coefficient . The primary enhancement in is due a reduction in the remanent strain of the ferroelectric layer caused by the lateral mismatch. Moreover, charge interphase layers in the composite can introduce an internal electric field, leading to a weaker large‐signal response compared with the composite with coherent interfaces.

Pyroelectric energy harvesting capabilities and electrocaloric effect in lead-free Sr Ba1-Nb2O6 ferroelectric ceramics - Hui Tang, Xin-Gui Tang, Ming-Ding Li, Qiu-Xiang Liu, Yan-Ping Jiang (Journal of Alloys and Compounds, 2019)

Solid-State Electrolytes for Lithium-Ion Batteries: Fundamentals, Challenges and Perspectives - Wenjia Zhao, Yi Jin, Ping He, Haoshen Zhou (Electrochemical Energy Reviews, 2019)
Abstract With the rapid popularization and development of lithium-ion batteries, associated safety issues caused by the use of flammable organic electrolytes have drawn increasing attention. To address this, solid-state electrolytes have become the focus of research for both scientific and industrial communities due to high safety and energy density. Despite these promising prospects, however, solid-state electrolytes face several formidable obstacles that hinder commercialization, including insufficient lithium-ion conduction and surge transfer impedance at the interface between solid-state electrolytes and electrodes. Based on this, this review will provide an introduction into typical lithium-ion conductors involving inorganic, organic and inorganic–organic hybrid electrolytes as well as the mechanisms of lithium-ion conduction and corresponding factors affecting performance. Furthermore, this review will comprehensively discuss emerging and advanced characterization techniques and propose underlying strategies to enhance ionic conduction along with future development trends. Graphical Abstract

A compact inorganic layer for robust anode protection in lithium‐sulfur batteries - Yuxing Yao, Xue‐Qiang Zhang, Bo‐Quan Li, Chong Yan, Pengyu Chen, Jia‐Qi Huang, Qiang Zhang (InfoMat, 2019)
Abstract Lithium‐sulfur (Li‐S) batteries are one of the most promising candidates for high energy density rechargeable batteries beyond current Li‐ion batteries. However, severe corrosion of Li metal anode and low Coulombic efficiency (CE) induced by the unremitting shuttle of Li polysulfides immensely hinder the practical applications of Li‐S batteries. Herein, a compact inorganic layer (CIL) formed by ex situ reactions between Li anode and ionic liquid emerged as an effective strategy to block Li polysulfides and suppress shuttle effect. A CE of 96.7% was achieved in Li‐S batteries with CIL protected Li anode in contrast to 82.4% for bare Li anode while no lithium nitrate was employed. Furthermore, the corrosion of Li during cycling was effectively inhibited. While applied to working batteries, 80.6% of the initial capacity after 100 cycles was retained in Li‐S batteries with CIL‐protected ultrathin (33 μm) Li anode compared with 58.5% for bare Li anode, further demonstrating the pot ential of this strategy for practical applications. This study presents a feasible interfacial regulation strategy to protect Li anode with the presence of Li polysulfides and opens avenues for Li anode protection in Li‐S batteries under practical conditions. image

Layer‐Based Heterostructured Cathodes for Lithium‐Ion and Sodium‐Ion Batteries - Ya‐Ping Deng, Zhenguo Wu, Ruilin Liang, Yi Jiang, Dan Luo, Aiping Yu, Zhongwei Chen (Advanced Functional Materials, 2019)
Abstract A critical bottleneck that hinders major performance improvement in lithium‐ion and sodium‐ion batteries is the inferior electrochemical activity of their cathode materials. While significant research progresses have been made, conventional single‐phase cathodes are still limited by intrinsic deficiencies such as low reversible capacity, enormous initial capacity loss, rapid capacity decay, and poor rate capability. In the past decade, layer‐based heterostructured cathodes acquired by combining multiple crystalline phases have emerged as candidates with a huge potential to realize performance breakthrough. Herein, recent studies on the structural properties, electrochemical behaviors, and synthesis route optimizations of these heterostructured cathodes are summarized for in‐depth discussions. Particular attention is paid to the latest mechanism discoveries and performance achievements. This review thus aims to promote a deeper understanding of the correlation between the cryst al structure of cathodes and their electrochemical behavior, and offers guidance to design advance cathode materials from the aspect of crystal structure engineering.

Re‐Engineering Poly(Acrylic Acid) Binder toward Optimized Electrochemical Performance for Silicon Lithium‐Ion Batteries: Branching Architecture Leads to Balanced Properties of Polymeric Binders - Sisi Jiang, Bin Hu, Zhangxing Shi, Wei Chen, Zhengcheng Zhang, Lu Zhang (Advanced Functional Materials, 2019)
Abstract Silicon is a promising anode material for lithium‐ion batteries with its superior capacity. However, the drastic volume changes during lithiation/delithiation cycles hinder the cycling performance, resulting in particle pulverization, conductivity loss, and an unstable electrode–electrolyte interface. Herein, a series of synthetic polymeric binders, poly(acrylic acid‐ co ‐tetra(ethylene glycol) diacrylate)—featuring a poly(acrylic acid) (PAA) backbone branched via tetra(ethylene glycol) diacrylate (TEGDA)—are developed that edge toward evidencing well‐balanced properties to confront capacity fading in Si‐based electrodes. The incorporation of ether chain not only leads to the branching architecture of the PAA backbone, thus affecting its mechanical properties, but also promotes the conductivity of Li ions. As a result, a synergistic performance improvement is observed in both half and full cells. The best‐performing cell using a branched PAA binder (bPAA) with a feeding molar ratio ([TEGDA]:[acrylic acid(AA)]) of 0.2 results in a 10% increase in initial capacity and a 31% increase in capacity retention over 100 cycles compared to the linear PAA cell. The cross‐sectional microscopic images of the cycled electrodes reveal that bPAA binders can drastically reduce the electrode expansion. This improvement results from the well‐balanced properties of the polymer design, which could guide further development for more advanced binder materials.

Single lithium-ion channel polymer binder for stabilizing sulfur cathodes - Chaoqun Niu, Jie Liu, Tao Qian, Xiaowei Shen, Jinqiu Zhou, Chenglin Yan (National Science Review, 2019)
Abstract Lithium–sulfur batteries have great potential for high-performance energy-storage devices, yet the severe diffusion of soluble polysulfide to electrolyte greatly limits their practical applications. To address the above issues, herein we design and synthesize a novel polymer binder with single lithium-ion channels allowing fast lithium-ion transport while blocking the shuttle of unnecessary polysulfide anions. In situ UV–vis spectroscopy measurements reveal that the prepared polymer binder has effective immobilization to polysulfide intermediates. As expected, the resultant sulfur cathode achieves an excellent specific capacity of 1310 mAh g−1 at 0.2 C, high Coulombic efficiency of 99.5% at 0.5 C after 100 cycles and stable cycling performance for 300 cycles at 1 C (1 C = 1675 mA g−1). This study reports a new avenue to assemble a polymer binder with a single lithium-ion channel for solving the serious problem of energy attenuation of lithium–sulfur batteries.

Tuning wettability of molten lithium via a chemical strategy for lithium metal anodes - Shuhua Wang, Junpei Yue, Wei Dong, Tong‐Tong Zuo, Jinyi Li, Xiaolong Liu, Xu‐Dong Zhang, Lin Liu, Ji‐Lei Shi, Ya‐Xia Yin, Yu‐Guo Guo (Nature Communications, 2019)
Metallic lithium affords the highest theoretical capacity and lowest electrochemical potential and is viewed as a leading contender as an anode for high-energy-density rechargeable batteries. However, the poor wettability of molten lithium does not allow it to spread across the surface of lithiophobic substrates, hindering the production and application of this anode. Here we report a general chemical strategy to overcome this dilemma by reacting molten lithium with functional organic coatings or elemental additives. The Gibbs formation energy and newly formed chemical bonds are found to be the governing factor for the wetting behavior. As a result of the improved wettability, a series of ultrathin lithium of 10-20 μm thick is obtained together with impressive electrochemical performance in lithium metal batteries. These findings provide an overall guide for tuning the wettability of molten lithium and offer an affordable strategy for the large-scale production of ultrathin lithium, an d could be further extended to other alkali metals, such as sodium and potassium.

Deactivation of redox mediators in lithium-oxygen batteries by singlet oxygen - Won‐Jin Kwak, Hun Kim, Yann K. Petit, Christian Leypold, Trung Thien Nguyen, Nika Mahne, Paul C. Redfern, Larry A. Curtiss, Hun‐Gi Jung, Sergey M. Borisov, Stefan A. Freunberger, Yang‐Kook Sun (Nature Communications, 2019)
Non-aqueous lithium-oxygen batteries cycle by forming lithium peroxide during discharge and oxidizing it during recharge. The significant problem of oxidizing the solid insulating lithium peroxide can greatly be facilitated by incorporating redox mediators that shuttle electron-holes between the porous substrate and lithium peroxide. Redox mediator stability is thus key for energy efficiency, reversibility, and cycle life. However, the gradual deactivation of redox mediators during repeated cycling has not conclusively been explained. Here, we show that organic redox mediators are predominantly decomposed by singlet oxygen that forms during cycling. Their reaction with superoxide, previously assumed to mainly trigger their degradation, peroxide, and dioxygen, is orders of magnitude slower in comparison. The reduced form of the mediator is markedly more reactive towards singlet oxygen than the oxidized form, from which we derive reaction mechanisms supported by density functional theory calculations. Redox mediators must thus be designed for stability against singlet oxygen.

Electrochemically primed functional redox mediator generator from the decomposition of solid state electrolyte - Matthew Li, Zhengyu Bai, Yejing Li, Lu Ma, Alvin Dai, Xuefeng Wang, Dan Luo, Tianpin Wu, Ping Liu, Lin Yang, Khalil Amine, Zhongwei Chen, Jun Lü (Nature Communications, 2019)
Recent works into sulfide-type solid electrolyte materials have attracted much attention among the battery community. Specifically, the oxidative decomposition of phosphorus and sulfur based solid state electrolyte has been considered one of the main hurdles towards practical application. Here we demonstrate that this phenomenon can be leveraged when lithium thiophosphate is applied as an electrochemically "switched-on" functional redox mediator-generator for the activation of commercial bulk lithium sulfide at up to 70 wt.% lithium sulfide electrode content. X-ray adsorption near-edge spectroscopy coupled with electrochemical impedance spectroscopy and Raman indicate a catalytic effect of generated redox mediators on the first charge of lithium sulfide. In contrast to pre-solvated redox mediator species, this design decouples the lithium sulfide activation process from the constraints of low electrolyte content cell operation stemming from pre-solvated redox mediators. Reasonable perf ormance is demonstrated at strict testing conditions.

Component‐Interaction Reinforced Quasi‐Solid Electrolyte with Multifunctionality for Flexible Li–O2 Battery with Superior Safety under Extreme Conditions - Chaozhu Shu, Jianping Long, Shi Xue Dou, Jiazhao Wang (Small, 2019)
Abstract High‐performance flexible lithium–oxygen (Li–O 2 ) batteries with excellent safety and stability are urgently required due to the rapid development of flexible and wearable devices. Herein, based on an integrated solid‐state design by taking advantage of component‐interaction between poly(vinylidene fluoride‐ co ‐hexafluoropropylene) and nanofumed silica in polymer matrix, a stable quasi‐solid‐state electrolyte (PS‐QSE) for the Li–O 2 battery is proposed. The as‐assembled Li–O 2 battery containing the PS‐QSE exhibits effectively improved anodic reversibility (over 200 cycles, 850 h) and cycling stability of the battery (89 cycles, nearly 900 h). The improvement is attributed to the stability of the PS‐QSE (including electrochemical, chemical, and mechanical stability), as well as the effective protection of lithium anode from aggressive soluble intermediates generated in cathode. Furthermore, it is demonstrated that the interaction among the components plays a pivotal role in modulating the Li‐ion conducting mechanism in the as‐prepared PS‐QSE. Moreover, the pouch‐type PS‐QSE based Li–O 2 battery also shows wonderful flexibility, tolerating various deformations thanks to its integrated solid‐state design. Furthermore, holes can be punched through the Li–O 2 battery, and it can even be cut into any desired shape, demonstrating exceptional safety. Thus, this type of battery has the potential to meet the demands of tailorability and comformability in flexible and wearable electronics.

Nonlinear optics of two‐dimensional transition metal dichalcogenides - Xinglin Wen, Zibo Gong, Dehui Li (InfoMat, 2019)
Abstract Nonlinear optics (NLO) of transition metal dichalcogenides (TMDs) is promising for the on‐chip photonic and optoelectronic applications. In this review, we will survey the current progress of NLO in TMDs. First, we will brief the basic theory of the NLO in TMDs. Second, several important nonlinear processes in TMDs such as harmonic generation, four‐wave mixing, saturable absorption, and two‐photon absorption will be presented and their potential applications are also discussed. Third, the main strategies to tune, modulate, and enhance the NLO in TMDs are reviewed, including the excitonic effect, symmetry modulation, optical cavity enhancement, valley selection, edge state, and material phase. Finally, we give an outlook regarding some important issues and directions of NLO in TMDs.

Two‐dimensional heterostructure promoted infrared photodetection devices - Gaofeng Rao, Xuepeng Wang, Yang Wang, Peihua Wangyang, Chaoyi Yan, Junwei Chu, Lanxin Xue, Chuanhui Gong, Jianwen Huang, Jie Xiong, Yanrong Li (InfoMat, 2019)
Abstract It is a rapidly developed subject in expanding the fundamental properties and application of two‐dimensional (2D) materials. The weak van der Waals interaction in 2D materials inspired researchers to explore 2D heterostructures (2DHs) based broadband photodetectors in the far‐infrared (IR) and middle‐IR regions with high response and high detectivity. This review focuses on the strategy and motivation of designing 2DHs based high‐performance IR photodetectors, which provides a wide view of this field and new expectation for advanced photodetectors. First, the photocarriers' generation mechanism and frequently employed device structures are presented. Then, the 2DHs are divided into semimetal/semiconductor 2DHs, semiconductor/semiconductor 2DHs, and multidimensional semi‐2DHs; the advantages, motivation, mechanism, recent progress, and outlook are discussed. Finally, the challenges for next‐generation photodetectors are described for this rapidly developing field.

Low‐dimensional nanomaterial/Si heterostructure‐based photodetectors - Wei Tian, Haoxuan Sun, Liang Chen, Peihua Wangyang, Xinrui Chen, Jie Xiong, Liang Li (InfoMat, 2019)
Abstract Due to its excellent electrical and optical features, silicon (Si) is highly attractive for photodetector applications. The design and fabrication of low‐dimensional semiconductor/Si hybrid heterostructures provide a great platform for fabricating high‐performance photodetectors, thereby overcoming the inherent limitations of Si. This review focuses on state‐of‐the‐art Si heterostructure‐based photodetectors. It starts with the introduction of three different device configurations, that is, photoconductors, photodiodes, and phototransistors. Their working mechanisms and relative pros and cons are introduced, and the figures of merit of photodetectors are summarized. Then, we discuss the device physics/design, photodetection performance, and optimization strategies for Si‐based photodetectors. Finally, future challenges in the photodetector applications of Si‐based hybrid heterostructures are discussed.

2D organic semiconductors, the future of green nanotechnology - Guru Prakash Neupane, Wendi Ma, Tanju Yildirim, Yilin Tang, Linglong Zhang, Yuerui Lu (Nano Materials Science, 2019)
The discovery of 2D organic semiconductors of atomically thin structures has attracted great attention due to their emerging optical, electronic, optoelectronic and mechatronic properties. Recent progress in such organic nanostructures has opened new opportunities for engineering material properties in many ways, such as, 0D/1D/2D nanoparticles hybridization, strain engineering, atomic doping etc. Moreover, 2D organic nanostructures exhibit a unique feature of bio–functionality and are highly sensitive to bio-analytes. Such peculiar behavior in 2D organics can be utilized to design highly-efficient bio-sensors. Also, a bio-molecular integrated electronic/optoelectronic device with enhanced performance can be attained. Furthermore, the bio-degradable, biocompatible, bio-metabolizable, non-toxic behaviour and natural origin of organic nanomaterials can address the current ecological concerns of increasing inorganic material based electronic waste. This review highlights the benefits of 2 D organic semiconductors. Considering the importance of strategic techniques for growing thin 2D organic layers, this review summarizes progress towards this direction. The possible challenges for long-time stability and future research directions in 2D organic nano electronics/optoelectronics are also discussed. We believe that this review article provides immense research interests in organic 2D nanotechnology for exploiting green technologies in the future.

Giant piezoresistive effect by optoelectronic coupling in a heterojunction - Thanh Nguyen, Toan Dinh, Abu Riduan Md Foisal, Hoang‐Phuong Phan, Tuan‐Khoa Nguyen, Nam‐Trung Nguyen, Dzung Viet Dao (Nature Communications, 2019)
Enhancing the piezoresistive effect is crucial for improving the sensitivity of mechanical sensors. Herein, we report that the piezoresistive effect in a semiconductor heterojunction can be enormously enhanced via optoelectronic coupling. A lateral photovoltage, which is generated in the top material layer of a heterojunction under non-uniform illumination, can be coupled with an optimally tuned electric current to modulate the magnitude of the piezoresistive effect. We demonstrate a tuneable giant piezoresistive effect in a cubic silicon carbide/silicon heterojunction, resulting in an extraordinarily high gauge factor of approximately 58,000, which is the highest gauge factor reported for semiconductor-based mechanical sensors to date. This gauge factor is approximately 30,000 times greater than that of commercial metal strain gauges and more than 2,000 times greater than that of cubic silicon carbide. The phenomenon discovered can pave the way for the development of ultra-sensitive s ensor technology.

An On‐Chip Quad‐Wavelength Pyroelectric Sensor for Spectroscopic Infrared Sensing - Thang Duy Dao, Satoshi Ishii, Anh Tung Doan, Yoshiki Wada, Akihiko Ohi, Toshihide Nabatame, Tadaaki Nagao (Advanced Science, 2019)
Abstract Merging photonic structures and optoelectronic sensors into a single chip may yield a sensor‐on‐chip spectroscopic device that can measure the spectrum of matter. In this work, an on‐chip concurrent multiwavelength infrared (IR) sensor, which consists of a set of narrowband wavelength‐selective plasmonic perfect absorbers combined with pyroelectric sensors, where the response of each pyroelectric sensor is boosted only at the resonance of the nanostructured absorber, is proposed and realized. The proposed absorber, which is based on Wood's anomaly absorption from a 2D plasmonic square lattice, shows a narrowband polarization‐independent resonance (quality factor – Q of 73) with a nearly perfect absorptivity as high as 0.99 at normal incidence. The fabricated quad‐wavelength IR sensors exhibit four different narrowband spectral responses at normal incidence following the predesigned resonances in the mid‐wavelength infrared region that corresponds to the atmospheric window. The device can be applied for practical spectroscopic applications such as nondispersive IR sensors, IR chemical imaging devices, pyrometers, and spectroscopic thermography imaging.

Quantum confinement-induced semimetal-to-semiconductor evolution in large-area ultra-thin PtSe2 films grown at 400 °C - Lida Ansari, Scott Monaghan, Niall McEvoy, Cormac Ó Coileáin, Conor P. Cullen, Jun Lin, Rita Siris, Tanja Stimpel‐Lindner, K. F. Burke, Gioele Mirabelli, Ray Duffy, Enrico Caruso, Roger Nagle, Georg S. Duesberg, Paul K. Hurley, Farzan Gity (npj 2D Materials and Applications, 2019)
Abstract In this work, we present a comprehensive theoretical and experimental study of quantum confinement in layered platinum diselenide (PtSe 2 ) films as a function of film thickness. Our electrical measurements, in combination with density functional theory calculations, show distinct layer-dependent semimetal-to-semiconductor evolution in PtSe 2 films, and highlight the importance of including van der Waals interactions, Green’s function calibration, and screened Coulomb interactions in the determination of the thickness-dependent PtSe 2 energy gap. Large-area PtSe 2 films of varying thickness (2.5–6.5 nm) were formed at 400 °C by thermally assisted conversion of ultra-thin platinum films on Si/SiO 2 substrates. The PtSe 2 films exhibit p -type semiconducting behavior with hole mobility values up to 13 cm 2 /V·s. Metal-oxide-semiconductor field-effect transistors have been fabricated using the grown PtSe 2 films and a gate field-controlled switching performance with an I ON / I O FF ratio of >230 has been measured at room temperature for a 2.5–3 nm PtSe 2 film, while the ratio drops to <2 for 5–6.5 nm-thick PtSe 2 films, consistent with a semiconducting-to-semimetallic transition with increasing PtSe 2 film thickness. These experimental observations indicate that the low-temperature growth of semimetallic or semiconducting PtSe 2 could be integrated into the back-end-of-line of a silicon complementary metal-oxide-semiconductor process.

Semiconductor nanowires: to grow or not to grow? - Paul C. McIntyre, Anna Fontcuberta i Morral (Materials Today Nano, 2019)

Photo-Atomic Layer Etching of GaAs/AlGaAs Nanoheterostructures - Mohammad R. Aziziyan, Hemant Sharma, Jan J. Dubowski (ACS Applied Materials & Interfaces, 2019)
High Resolution Image Download MS PowerPoint Slide Photo-atomic layer etching (photo-ALE) of GaAs and AlGaAs semiconductors was investigated in deionized H 2 O and aqueous solution of NH 4 OH under weak excitation conditions ( P ≈ 20 mW/cm 2 ). The process is based on digital photocorrosion in a processed solution and a negligible corrosion during the light-off phase employed for dissolution of the photocorrosion products. An inductively coupled plasma mass spectroscopy (ICP-MS) analysis revealed that photo-ALE of GaAs in an aqueous solution of NH 4 OH proceeds linearly with the number of reaction cycles, typically at ∼0.1 nm/cycle, and with the light-off phase as short as 22 s sufficient to entirely dissolve the photocorrosion products generated during a 3 s irradiation. In agreement with the ICP-MS data, the constant photo-ALE rates in NH 4 OH were also demonstrated in situ with the photoluminescence measurements. Our results suggest that the congruent decomposition of III–V material s and the etching of deep structures with atomic layer resolution could be facilitated by switching in situ between different etching environments.

Surface-grafting polymers: from chemistry to organic electronics - Shuguang Wang, Zhongwu Wang, Jie Li, Liqiang Li, Wenping Hu (Materials Chemistry Frontiers, 2019)
This review comprehensively summarizes the recent progress in surface-grafting polymers, including their formation process and the utilization of surface-grafting polymers as functional materials of insulators, conductors and semiconductors in versatile organic electronic devices.

Deep-ultraviolet integrated photonic and optoelectronic devices: A prospect of the hybridization of group III–nitrides, III–oxides, and two-dimensional materials - Nasir Alfaraj, Jung‐Wook Min, Chun Hong Kang, Abdullah A. Alatawi, Davide Priante, Ram Chandra Subedi, Malleswararao Tangi, Tien Khee Ng, Boon S. Ooi (Journal of Semiconductors, 2019)
Abstract Progress in the design and fabrication of ultraviolet and deep-ultraviolet group III–nitride optoelectronic devices, based on aluminum gallium nitride and boron nitride and their alloys, and the heterogeneous integration with two-dimensional and oxide-based materials is reviewed. We emphasize wide-bandgap nitride compound semiconductors (i.e., (B, Al, Ga)N) as the deep-ultraviolet materials of interest, and two-dimensional materials, namely graphene, two-dimensional boron nitride, and two-dimensional transition metal dichalcogenides, along with gallium oxide, as the hybrid integrated materials. We examine their crystallographic properties and elaborate on the challenges that hinder the realization of efficient and reliable ultraviolet and deep-ultraviolet devices. In this article we provide an overview of aluminum nitride, sapphire, and gallium oxide as platforms for deep-ultraviolet optoelectronic devices, in which we criticize the status of sapphire as a platform for efficie nt deep-ultraviolet devices and detail advancements in device growth and fabrication on aluminum nitride and gallium oxide substrates. A critical review of the current status of deep-ultraviolet light emission and detection materials and devices is provided.

Recent advances in lithographic fabrication of micro-/nanostructured polydimethylsiloxanes and their soft electronic applications - Donghwi Cho, Junyong Park, Taehoon Kim, Seokwoo Jeon (Journal of Semiconductors, 2019)
Abstract The intensive development of micro-/nanotechnologies offers a new route to construct sophisticated architectures of emerging soft electronics. Among the many classes of stretchable materials, micro-/nanostructured poly(dimethylsiloxane) (PDMS) has emerged as a vital building block based on its merits of flexibility, stretchability, simple processing, and, more importantly, high degrees of freedom of incorporation with other functional materials, including metals and semiconductors. The artificially designed geometries play important roles in achieving the desired mechanical and electrical performances of devices and thus show great potential for applications in the fields of stretchable displays, sensors and actuators as well as in health-monitoring device platforms. Meanwhile, novel lithographic methods to produce stretchable platforms with superb reliability have recently attracted research interest. The aim of this review is to comprehensively summarize the progress regardi ng micro-/nanostructured PDMS and their promising soft electronic applications. This review is concluded with a brief outlook and further research directions.

Infrared tunable, two colour-band photodetectors on flexible platforms using 0D/2D PbS–MoS2 hybrids - Subhrajit Mukherjee, Subhajit Jana, Tridib Kumar Sinha, Soumen Das, S. K. Ray (Nanoscale Advances, 2019)
visible broadband and wavelength selective short-wave IR photodetectors. Devices have also been demonstrated on polyethylene terephthalate substrates using a solution-based synthesis technique for flexible and ultrathin optoelectronic device applications. The photodetection performance of fabricated devices suggests that the synergic 0D/2D hybrid nanostructures are significantly superior to solution processed hybrid devices operating in the infrared region. The successful integration of 0D QDs in 2D materials may pave the way for novel, high performance, next-generation CMOS compatible flexible photonic devices.

The third digital divide and Bourdieu: Bidirectional conversion of economic, cultural, and social capital to (and from) digital capital among young people in Madrid (New Media & Society, 2020)
Based on Bourdieu’s theory, this article focuses on the third-level digital divide in relation to offline outcomes of Internet use. Based on 30 in-depth qualitative interviews with young people in Madrid, we analyzed the mechanisms used to convert three main forms of capital—economic, cultural, and social—into digital capital (DC) and the subsequent reconversion of DC back into the three main forms of capital. We conclude that economic capital is the most basic form of digital inequality, imposing material barriers to access. Cultural capital is transformed into DC through people’s technosocialization, while social capital is converted into DC by means of social practices and social support. DC can be retransformed into each of the three main forms of capital: to economic capital by means of professional networking and access to goods; to cultural capital through access to knowledge; and into social capital by the differential management of social ties.

Enhancing the current density of a piezoelectric nanogenerator using a three-dimensional intercalation electrode - Gu L, Liu J, Cui N, Xu Q, Du T, Zhang L, Wang Z, Long C, Qin Y. (Nature Communications, 2020)
Long Gu1,3, Jinmei Liu1,3, Nuanyang Cui1, Qi Xu 1, Tao Du1, Lu Zhang1, Zheng Wang1, Changbai Long1 & The low output current density of piezoelectric nanogenerators (PENGs) severely restricts their application for ambient mechanical energy harvest. This has been a key challenge in the development of PENG. Here, to conquer this, based on a piezoelectric material with high piezoelectric coefﬁcient (Sm-PMN-PT), a new design of PENG with a three-dimensional intercalation electrode (IENG) is proposed. By creating many boundary interfaces inside the piezoelectric material, the total amount of surface polarization charges increased, which contributes to an increased current density. The IENG can output a maximum peak shortcircuit current of 320 μA, and the corresponding current density 290 μA cm−2 is 1.93 and 1.61 times the record values of PENG and triboelectric nanogenerator (TENG), respectively. It can also charge a 1 μF capacitor from 0 V to 8 V in 21 cycles, and the equivalent surface cha rge density 1690 μC m−2 is 1.35 times the record value of TENG.

Polyvinylidene Fluoride-Added Ceramic Powder Composite Near-Field Electrospinned Piezoelectric Fiber-Based Low-Frequency Dynamic Sensors - Pan CT, Wang SY, Yen CK, Kumar A, Kuo SW, Zheng JL, Wen ZH, Singh R, Singh SP, Khan MT, Chaudhary RK, Dai X, Chandra Kaushik A, Wei DQ, Shiue YL, Chang WH. (ACS Omega, 2020)
In this study, near-ﬁeld electrospinning (NFES) is used to fabricate BaxSr1−xTiO3 (BST)/poly(vinylidene ﬂuoride) (PVDF) piezoelectric ﬁber composites with excellent mechanical properties and chemical properties. BST ceramic powder is blended with PVDF solution uniformly to prepare a solution of appropriate conductance. The parameter for BST/PVDF ﬁber processing is based on PVDF ﬁbers. Scanning electron microscopy, diﬀerential scanning calorimetry, microtensile testing, Fourier transform infrared spectroscopy, and electricity test of the blends of BST/PVDF ﬁbers are incorporated. Mechanical properties of the ﬁbers are then measured by microtensile testing. Eﬀects of distinct ratios of Ba/Sr and the content of Ba0.7Sr0.3TiO3 ceramic powder on BST/PVDF piezoelectric ﬁbers are discussed. Finally, BST/PVDF piezoelectric ﬁber composites are patterned on a poly(ethylene terephthalate) (PET)-based structure with an interdigital electrode as a BST/PVDF ﬂexible energy harvester to capture ambien t energy. The results show that the BST ceramic powder is ∼58−93 nm, and the diameters of piezoelectric ﬁber composites are ∼6.8−13.7 μm. The tensile strength of piezoelectric ﬁber composites is ∼74.92 MPa, and the Young’s coeﬃcient tensile strength is ∼3.74 GPa. Mechanical properties are 2−3 times higher than those of pure PVDF piezoelectric ﬁbers. The maximum open-circuit voltage and closed-loop current of BST/PVDF ﬁbers reached ∼1025 mV and ∼391 nA, respectively. The electromechanical energy conversion eﬃciency of the BST/PVDF energy harvester is found to be 1−2 times higher than that of the PVDF energy harvester. It is conﬁrmed and validated that the addition of BST ceramic powder could eﬀectively increase the piezoelectric constant of PVDF piezoelectric ﬁbers.

Enhanced piezoelectric performance of BiCl3/PVDF nanofibers-based nanogenerators (Composites Science and Technology, 2020)
BiCl3, because of its promoting the formation of beta crystal of PVDF and enhancing the conductivity, has drawn increasing attention in the fields of PVDF piezoelectric applications. The high beta-phase concentration was achieved from the nanofiber film of PVDF doped with BiCl3, which enhance the piezoelectric power output of the fiber films. Under vertical vibration, the output piezoelectric voltage of BiCl3/PVDF nanofiber film-based piezoelectric nanogenerator with an optimized ratio of 2 wt% is up to 1.1 V, which is 4.76 times higher than that of pure PVDF fiber piezoelectric nanogenerator. The maximum peak current and power surface density are 2 mu A and 0.2 mu W cm(-2), respectively. The alternating output signals generated from the BiCl3 /PVDF fiber film can be used to charge a capacitor through a bridge rectifier and then light up a red LED. The test method had great influence on the piezoelectric outputs of the piezoelectric device. When a piezoelectric device is impacted by a falling ball, it can produce a voltage output of 38 V. This study shows that the BiCl3/PVDF nanofiber film based piezoelectric nanogenerator is a promising mechanical energy harvesters for portable electronic and wearable devices.

Effect of polyvinylidene fluoride on the acoustic impedance matching, poling enhancement and piezoelectric properties of 0–3 smart lead-free piezoelectric Portland cement composites (Journal of Electroceramics, 2020)
Smart composites, which are composed of piezoelectric ceramics and cement-based materials, have been developed for sensing and health monitoring of concrete infrastructure. Barium titanate (BT)-Portland cement (PC)-polyvinylidene fluoride (PVDF) composites with 40-60 vol.% BT particles (with a median size of similar to 425 mu m) and 0-7 vol.% PVDF were fabricated by the pressing and curing method. The effects of the PVDF content on the acoustic impedance (Z(c)), dielectric constant (epsilon(r)). piezoelectric charge coefficient (d(33)) and piezoelectric voltage coefficient (g(33)) of the BT-PC-PVDF composites were investigated. Increasing the PVDF content in the composites led to a decrease in the Z(c) value so that it approached that of concrete. The PC phase was replaced by the PVDF phase in the BT-cement-based composites to reduce the leakage current in these composites. As a result, the piezoelectric properties of the BT-PC-PVDF composites improved noticeably. BT contents of 50 and 60 vol.% and a PVDF of 5 vol.% had the highest d(33)-24-25 pC/N. Moreover, the composite with 50 vol.% BT and 5 vol.% PVDF had the highest piezoelectric voltage coefficient herein (g(33)=14.6 x 10(-3)V.m/N).

Thermally Stable Poly(vinylidene fluoride) for High-Performance Printable Piezoelectric Devices - Lin J, Malakooti MH, Sodano HA. (ACS Applied Materials & Interfaces, 2020)
Piezoelectric polymers, such as poly(vinylidene fluoride) (PVDF) and its copolymers, can achieve large strains and high work density under external electrical fields. These materials are highly desirable in the development of electronic devices and intelligent structures. Here, we demonstrate that dehydrofluorination (DHF) can provide a versatile chemical modification of the PVDF homopolymer that yields thermally stable ferroelectricity. The DHF process significantly increases the fraction of planar chain conformation in the PVDF and results in higher piezoelectric coupling with a wider processing temperature range, compared to traditionally processed PVDF. The efficacy of DHF in promoting planar chain conformation is demonstrated through molecular simulation and further proven by experimental characterization. The induced piezoelectric phases by DHF were able to be preserved through high temperature treatments up to 200 °C. The dehydrofluorinated PVDF exhibits improved electromechanic al coupling with a high piezoelectric strain coefficient of d31 = 25.12 ± 1.13 pC/N, which can be further improved to 35.12 ± 0.69 pC/N by common mechanical drawing. This high piezoelectric voltage coefficient leads to an excellent actuation and energy harvesting behavior with a power density of 21.96 mW/cm3 in a flexible undrawn PVDF energy harvester, which is 3.13 times higher than conventionally drawn PVDF. The versatile and scalable method for preparing PVDF polymers with high piezoelectric coupling will enable new manufacturing processes not currently compatible with PVDF homopolymers.

A flexible piezoelectric pressure sensor based on PVDF nanocomposite fibers doped with PZT particles for energy harvesting applications - Negar Chamankar, Ramin Khajavi, Ali Akbar Yousefi, Abosaeed Rashidi, Farhad Golestanifard (Ceramics International, 2020)
Flexible piezoelectric energy harvesters are a suitable choice for scavenging wasted mechanical energy because of the high demand for sustainable power sources. Flexible pressure sensors based on PVDF-PZT nanocomposite with different PZT volume fractions (0.011, 0.041, 0.096, 0.17, 0.3, and 0.37) were prepared in the form of fibers through an electrospinning method for piezoelectric energy harvesting application. According to the results, dielectric constant and piezoelectric coefficients (epsilon) piezoelectric coefficient, and figure of merit) gradually increased with the doping of PZT particles into PVDF fibers. Dielectric constant (e), piezoelectric coefficient (d), and figure of merit (d x g) for PVDF-PZT nanocomposite with 0.011 PZT volume fraction were 37.29, 10.51 pCN(-1), and 33.46 x 10(-16) m(2)/N, respectively, and increased to 104.81, 22.93 pCN(-1), and 56.68 x 10(-16) m(2)/N for PVDF-PZT nanocomposite fibers with a volume fraction of 0.37. As piezoelectric energy harvester s, piezoelectric sensitivity of PVDF-PZT nanocomposite fibers rose with increasing the PZT volume fraction. The generated output voltage was 184 mV under an applied force of 2.125 N with the piezoelectric sensitivity calculated as 173.507mV/N mu m for PVDF-PZT nanocomposite fibers with 0.37 PZT volume fractions which increased compared to pristine PVDF fibers (generated output voltage = 22 mV under applied force 2.4 N, piezoelectric sensitivity = 29.49 mV/N mu m). The achieved output power density of PVDF-PZT nanocomposite fibers with 0.37 PZT volume fractions was obtained 30.69 mu W cm(-2 )higher than PVDF-PZT nanocomposite fibers with 0.011 PZT volume fractions (18.44 mu W cm(-2)).

Design, Assembly and Testing of a Novel Piezoelectric Geophone Based on PVDF Film (Integrated ferroelectrics, 2020)
A piezoelectric geophone is a vibration transducer that converts mechanical vibrations into electrical signals via the piezoelectric effect. At present, the commonly used sensitive component of the conventional piezoelectric geophone is piezoelectric ceramic (PZT) material, which has low structural flexibility and high natural frequency. This paper reports a piezoelectric geophone based on polyvinylidene fluoride (PVDF) film with a sensitive unit composed of PVDF film and spiral cantilever beam, which can increase the sensitivity and reduce the low-frequency cutoff frequency. Firstly, the PVDF piezoelectric film is introduced, and the sensitive unit with PVDF piezoelectric film and spiral cantilever beam is designed. Secondly, the signal conditioning circuit and the digital module circuit are designed according to the characteristics of the detector and the test environment. Finally, the performance tests and fabrication of the geophone are carried out. The results indicate that the pi ezoelectric geophone has a stable sensitivity of 230 mV/m/s2 in the range of 4–90 Hz, which are superior to the existing piezoelectric geophone.

Enhanced airborne sound absorption effect in poly(vinylidene fluoride)/(K0.5Na0.5)NbO3‐nanofiber composite foams (Journal of Applied Polymer Science, 2020)
Abstract Introducing electrical conductive function to discharge local piezoelectric effect is found effective for improving airborne sound absorption performance. In this work, instead of conductive fillers, a composite with two piezoelectric materials with opposite piezoelectric responses was explored aiming at enhanced sound absorption effect. Open‐cell poly(vinylidene fluoride)/(K 0.5 Na 0.5 )NbO 3 (PVDF/KNN)‐nanofiber composite foams were proposed and investigated for airborne sound absorption purpose. Structural and thermal analyses showed that the KNN nanofibers were well dispersed in the PVDF matrix and enhanced the degree of crystallinity of polar phase of PVDF. Significantly enhanced airborne sound absorption over a broad frequency range was observed in the PVDF/KNN‐nanofiber composite foams, with increasing KNN nanofibers. One possible mechanism for the improved sound absorption with the piezoelectric KNN nanofibers with positive piezoelectric coefficient added in the PVDF m atrix with negative piezoelectric coefficient is that electrical discharge could be facilitated for energy dissipation with the opposite charges generated through the piezoelectric effects in the two phases with opposite polarity. The experimental results show that the open‐cell PVDF/KNN‐nanofiber composite foams are promising for broadband airborne sound absorption application, and our analysis shed a light on the strategy in designing piezoelectric composite foam with high sound absorption performance.

Flexible Piezoelectric Pressure Tactile Sensor Based on Electrospun BaTiO3/Poly(vinylidene fluoride) Nanocomposite Membrane - Jiang, Jie; Tu, Shijian; Fu, Runfang; Li, Jingjing; Hu, Fei; Yan, Bin; Gu, Yingchun; Chen, Sheng (ACS APPLIED MATERIALS & INTERFACES, 2020)
Poly(vinylidene fluoride) (PVDF)-based piezoelectric materials are promising candidates for sensors, transducers, and actuators, due to several distinctive characteristics such as good flexibility, easy processability, and high mechanical resistance. In the present work, PVDF-based nanocomposites loaded with BaTiO3 nanoparticles (NPs) of various weight fractions were prepared by the electrospinning technique and used for the fabrication of a flexible piezoelectric pressure tactile sensor (PPTS). The addition (5, 10, and 20 wt %) of piezoelectric BaTiO3 NPs improves the piezoelectric performance, especially the ss phase crystals of PVDF/BaTiO3 (10 wt %) nanocomposites that can reach 91.0%. In addition, the mechanical strength of PVDF/BaTiO3 nanocomposites is up to 26.7 MPa, which is an increase of 66% compared to neat PVDF. It should be emphasized that the elongation at break continuously increases from 71% to 153% with increasing BaTiO3 NPs. More importantly, the PPTS (piezoelectric pr essure tactile sensor) with the combination of electrospun PVDF/BaTiO3 nanocomposite membranes and polydimethylsiloxane (PDMS) displays excellent flexibility and linear response to external mechanical force. The flexible PPTS devices capable of detecting different music sounds have potential uses in wide fields, such as voice recognition, speech therapy, and ultrasound imaging.

Theoretical Model and Outstanding Performance from Constructive Piezoelectric and Triboelectric Mechanism in Electrospun PVDF Fiber Film - Yousry, Yasmin Mohamed; Yao, Kui; Mohamed, Ayman Mahmoud; Liew, Weng Heng; Chen, Shuting; Ramakrishna, Seeram (ADVANCED FUNCTIONAL MATERIALS, 2020)
Flexible materials with high electromechanical coupling performance are highly demanded for wide applications for electromechanical sensors and transducers, including mechanical energy harvesters. Here, outstanding electromechanical performance is obtained in electrospun-aligned polyvinylidene fluoride (PVDF) fiber film. A theoretical model is developed from systematic theoretical analyses to clarify the underlying constructive piezoelectric-triboelectric mechanism in the polarized PVDF fiber films that explains the experimental observations well. The electrospinning process induces polarization alignment and thus tunes the electron affinity for PVDF fibers with different polarization terminals, which results in the constructive piezoelectric and triboelectric responses in the obtained PVDF fiber films. Extremely large effective piezoelectric performance properties are achieved in the direct piezoelectric measurements, reaching the maximum effective piezoelectric strain and voltage coe fficients of -1065 pm V-1 and -9178 V mm N-1, respectively, at 100 Hz. In the converse piezoelectric measurements without a significant contribution from reversible triboelectric effect, the maximum effective piezoelectric strain and voltage coefficients are -166 pm V-1 and -1499 V mm N-1, respectively. The theoretical analyses and experimental results show the great potential of the electrospun aligned polar PVDF fiber material for various electromechanical device applications, particularly for mechanical energy harvesting.

Structure-Properties Relationship of Electrospun PVDF Fibers - Castkova K, Kastyl J, Sobola D, Petrus J, Stastna E, Riha D, Tofel P. (Fibers, 2020)
Electrospinning as a versatile technique producing nanoﬁbers was employed to study the inﬂuence of the processing parameters and chemical and physical parameters of solutions on poly(vinylidene ﬂuoride) (PVDF) ﬁbers’ morphology, crystallinity, phase composition and dielectric and piezoelectric characteristics. PVDF ﬁbrous layers with nano- and micro-sized ﬁber diameters were prepared by a controlled and reliable electrospinning process. The ﬁbers with diameters from 276 nm to 1392 nm were spun at a voltage of 25 kV–50 kV from the pure PVDF solutions or in the presence of a surfactant—Hexadecyltrimethylammonium bromide (CTAB). Although the presence of the CTAB decreased the ﬁbers’ diameter and increased the electroactive phase content, the piezoelectric performance of the PVDF material was evidently deteriorated. The maximum piezoelectric activity was achieved in the ﬁbrous PVDF material without the use of the surfactant, when a piezoelectric charge of 33 pC N−1 was measured in the tran sversal direction on a mean ﬁber diameter of 649 nm. In this direction, the material showed a higher piezoelectric activity than in the longitudinal direction.

Novel Hybrid Pressure Sensor Based on Electrospun Spandex-Polyvinylidene Fluoride Composite Nanofiber Webs - Reza, Mohammad Shamim; Kim, Kap Jin; Kim, Hongdoo (FIBERS AND POLYMERS, 2020)
In this study, the mixture solution of Spandex and polyvinylidene fluoride (PVDF) was electrospun under controlled compositions to obtain Spandex-PVDF hybrid nanofiber webs. Their physico-mechanical and piezo-responsive behaviors were investigated. When the dynamically changing force was applied to this hybrid sensor, dynamic pressure could be measured through the electric current generated by the orientational change of C-F dipoles in the PVDF part of the composite nanoweb as a function of time. When the static force was applied to this hybrid sensor, static pressure could be measured through the increasing capacitance value caused by the decreasing thickness of the composite nanoweb rather than the piezoelectric current. The piezoelectric and piezocapacitive properties of this hybrid sensor could be measured simultaneously using a piezoelectric amplifier and an LCR meter, respectively. Overall, 25-50 wt.% addition of PVDF in Spandex greatly enhanced the piezoelectric output signal as well as reduced pressure-capacitance hysteresis and higher capacitance change with the applied pressure due to the rubbery Spandex of this hybrid sensor. Moreover, AgNO3, which acts as a precursor of silver nano-particle (AgNP) formed in the electrospun PVDF nanoweb, was added into the PVDF/Spandex electrospun solution to get enhanced piezoelectric performance of the hybrid sensor caused by the preferential formation of beta-phase of PVDF. The results are reported in detail.

A comparative study of electrospun polyvinylidene fluoride and poly(vinylidenefluoride-co-trifluoroethylene) fiber webs: Mechanical properties, crystallinity, and piezoelectric properties - Zhang, Wenxin; Zaarour, Bilal; Zhu, Lei; Huang, Chen; Xu, Bugao; Jin, Xiangyu (JOURNAL OF ENGINEERED FIBERS AND FABRICS, 2020)
Energy scavenging has been attracting the consideration of researchers in recent years. In this study, the fabrication and characterization of electrospun randomly oriented and aligned grooved polyvinylidene fluoride (PVDF) and poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE) fiber webs are studied. The fibers are generated with comparable diameters and the webs which are used as an active layer to directly make a piezoelectric nanogenerator are fabricated with the same thickness for accurate comparison. The results show that PVDF-TrFE fiber webs have better mechanical properties, crystallinity, and piezoelectric properties than PVDF fiber webs. Furthermore, the piezoelectric nanogenerator based on PVDF-TrFE fiber webs has higher electrical outputs than piezoelectric nanogenerator based on PVDF fiber webs owing to its high beta phase content (F(beta)). Moreover, the electrical outputs of the piezoelectric nanogenerator based on aligned fiber webs are higher than those based on randomly oriented fiber webs due to the increase in the friction area. We believe that our work can be served as a good reference for the comparison between the mechanical, physicochemical, and piezoelectric properties of PVDF and PVDF-TrFE fiber webs generated via electrospinning.

Precipitation-Printed High-β Phase Poly(vinylidene fluoride) for Energy Harvesting - Tu, Ruowen; Sprague, Ethan; Sodano, Henry A. (ACS APPLIED MATERIALS & INTERFACES, 2020)
Poly(vinylidene fluoride) (PVDF) possesses outstanding piezoelectric properties, which allows it to be utilized as a functional material. Being a semicrystalline polymer, enhancing the piezoelectric properties of PVDF through the promotion of the polar beta phase is a key research focus. In this research, precipitation printing is demonstrated as a scalable and tailorable approach to additively manufacture complex and bulk 3D piezoelectric energy harvesters with high-beta phase PVDF. The beta-phase fraction of PVDF is improved to 60% through precipitation printing, yielding more than 200% improvement relative to solvent-cast PVDF films. Once the precipitation-printed PVDF is hot-pressed to reduce internal porosity, a significant ferroelectric response with a coercive field of 98 MV m(-1) and a maximum remnant polarization of 3.2 mu C cm(-2) is observed. Moreover, the piezoelectric d(33) and d(31) coefficients of printed then hot-pressed PVDF are measured to be -6.42 and 1.95 pC N-1, re spectively. For energy-harvesting applications, a stretching d(31)-mode energy harvester is demonstrated to produce a power density of up to 717 mu W cm(-3), while a printed full-scale heel insole with embedded d(33)-mode energy harvesting is capable of successfully storing 32.2 mu J into a capacitor when used for 3 min. Therefore, precipitation printing provides a new method for producing high-beta phase PVDF and bulk piezoelectric energy harvesters with the advantages of achieving geometry complexity, fabrication simplicity, and low cost.

Enhanced Piezoelectricity of Electrospun Polyvinylidene Fluoride Fibers for Energy Harvesting - Szewczyk, Piotr K.; Gradys, Arkadiusz; Kim, Sung Kyun; Persano, Luana; Marzec, Mateusz; Kryshtal, Aleksandr; Busolo, Tommaso; Toncelli, Alessandra; Pisignano, Dario; Bernasik, Andrzej; Kar-Narayan, Sohini; Sajkiewicz, Pawel; Stachewicz, Urszula (ACS APPLIED MATERIALS & INTERFACES, 2020)
Piezoelectric polymers are promising energy materials for wearable and implantable applications for replacing bulky batteries in small and flexible electronics. Therefore, many research studies are focused on understanding the behavior of polymers at a molecular level and designing new polymer-based generators using polyvinylidene fluoride (PVDF). In this work, we investigated the influence of voltage polarity and ambient relative humidity in electrospinning of PVDF for energy-harvesting applications. A multitechnique approach combining microscopy and spectroscopy was used to study the content of the beta-phase and piezoelectric properties of PVDF fibers. We shed new light on beta-phase crystallization in electrospun PVDF and showed the enhanced piezoelectric response of the PVDF fiber-based generator produced with the negative voltage polarity at a relative humidity of 60%. Above all, we proved that not only crystallinity but also surface chemistry is crucial for improving piezoelectr ic performance in PVDF fibers. Controlling relative humidity and voltage polarity increased the d(33) piezoelectric coefficient for PVDF fibers by more than three times and allowed us to generate a power density of 0.6 mu W.cm(-2) from PVDF membranes. This study showed that the electrospinning technique can be used as a single-step process for obtaining a vast spectrum of PVDF fibers exhibiting different physicochemical properties with beta-phase crystallinity reaching up to 74%. The humidity and voltage polarity are critical factors in respect of chemistry of the material on piezoelectricity of PVDF fibers, which establishes a novel route to engineer materials for energy-harvesting and sensing applications.

Piezoelectric Hybrid Heterostructures PVDF/(Ba,Ca)(Zr,Ti)O3 Obtained by Laser Techniques - Enea, Nicoleta; Ion, Valentin; Moldovan, Antoniu; Bonciu, Anca; Scarisoreanu, Nicu Doinel (COATINGS, 2020)
In this paper we report the development of thin films composed of two piezoelectric materials, namely (Ba(Ti0.8Zr0.2)O-3-x(Ba0.7Ca0.3)TiO3 (BCTZ) and polyvinylidene difluoride (PVDF), thus obtaining high piezoelectric hybrid heterostructures for making them a viable option for wearable pressure sensors. The piezoelectric output response as a function of different weight percentage of BCTZ ceramic powders (x = 0.50 BCTZ50 and x = 0.55 BCTZ55) in the PVDF matrix was investigated. The highest value of the piezoelectric coefficient d33 and the capacitance, with low dielectric loss was obtained for the heterostructure composed of PVDF/BCTZ50.

Piezoelectric and mechanical properties of PVDF-PZT composite - Pradhan, Sudipta Kishore; Kumar, Amit; Kour, P.; Pandey, Rabichandra; Kumar, Pawan; Kar, Manoranjan; Sinha, A. N. (FERROELECTRICS, 2020)
(100 - x)PVDF-(x) PZT (PVDF: Polyvinylidene Difluoride and PZT: Lead Zirconate Titanate) composite was prepared in 0-3 connectivity by the solvent casting methods. The piezoelectric co-efficient is found to be increased with the increase in PZT concentration in the PVDF matrix. It is due to the increase of beta phase of PVDF as well as lattice strain in PZT. The incorporation of PZT ceramics in the PVDF matrix causes an increase in storage loss modulus of the sample. The tan delta decreases due to incorporation of PZT ceramics in the PVDF matrix. The piezoelectric and mechanical properties are found to be increased in the PVDF-PZT composite compare to that of PVDF.

Development of a new flexible nanogenerator from electrospun nanofabric based on PVDF/talc nanosheet composites - Shetty, Sawan; Mahendran, Arunjunairaj; Anandhan, S. (SOFT MATTER, 2020)
Herein, a flexible piezoelectric nanogenerator composed of electrospun talc/PVDF [poly(vinylidene fluoride)] nanocomposite fabrics has been developed. These nanocomposite fabrics demonstrated enhanced mechanical and piezoelectric properties compared with pristine PVDF nanofabrics. In particular, nanocomposite fabrics with 0.50 wt% talc yielded 89.6% of polar beta-phase in the PVDF matrix, thereby augmenting its piezoelectric response. X-ray diffraction, Fourier transform infrared spectroscopy, and differential scanning calorimetry conclusively affirmed the promotion of polar beta-phase in the talc/PVDF nanocomposite fabrics. The 0.50 wt% talc/PVDF nanocomposite fabric based nanogenerator produced an open-circuit voltage and power density of 9.1 V and 1.12 mu W cm(-2), respectively, under repetitive finger tapping mode (under a load of 3.8 N). Furthermore, the nanogenerator was also subjected to frequency modulated-shaker mode, wherein an output voltage of 8.9 V was produced. Improved f lexibility, mechanical robustness, and enhanced piezoelectric responsiveness of this nanogenerator could possibly pave the way for its use in portable self-powered devices.

Metal-organic frameworks Co3[Co(CN)6]2: A promising candidate for dramatically reinforcing the piezoelectric activity of PVDF - Yang, Lu; Qiu, Tianzheng; Shen, Mingxia; He, Haiyan; Huang, Huajie (COMPOSITES SCIENCE AND TECHNOLOGY, 2020)
Over decades, the exploration of poly(vinylidene fluoride) (PVDF) based composites with outstanding piezoelectric activity has gained great popularity and interest from diverse research communities because of their potential in realizing flexible sensors and energy harvesters. Herein, in this work, we reported a novel high performance PVDF based piezoelectric composites containing Metal-organic frameworks (MOF) Co-3[Co(CN)(6)](2). The ultra-high specific surface area and unique open framework nanostructure of Co-3[Co(CN)(6)](2) demonstrated to be efficient in inducing strong interfacial coupling effect within PVDF, resulting in piezoelectricity enhancement. Moreover, the redox behavior of metal ions in Co-3[Co(CN)(6)](2 )which provides pathway for electrons, was anticipated to further hardness the interfacial coupling effect and consequently piezoelectric reinforcing effect. Upon an addition of 0.6 wt% Co-3[Co(CN)(6)](2), the piezoelectric response of composites reached the maximum, i. e. a d(33) and a d(31) of 37 pC/N and 33 pC/N, respectively, which are both almost double those of PVDF. Furthermore, the resultant composites exhibited superior electromechanical coupling factor k(31) up to 0.135 while that of pure PVDF was only 0.078. For the first time, we present the applicability of MOF as a new class of reinforcing fillers for piezoelectric composites, providing a new perspective to develop PVDF based composites with superior piezoelectric response.

Flexible textured MnO2 nanorods/PVDF hybrid films with superior piezoelectric performance for energy harvesting application - Zhao, Qiuying; Yang, Lu; Chen, Kaineng; Ma, Yizhou; Peng, Qirui; Ji, Hongli; Qiu, Jinhao (COMPOSITES SCIENCE AND TECHNOLOGY, 2020)
To date, the fabrication of high-performance flexible energy harvesters/nanogenerators based on piezoelectric poly(vinyldene fluoride) (PVDF) is of great concern due to their huge potential to realize full-flexible self-powered electronics. Herein, in this work, we report a flexible piezoelectric nanogenerator (PNG) based on a textured hybrid film consisting of PVDF and manganese dioxide (MnO2) nanorods. It is found that the combination of MnO2 and PVDF can notably facilitate the formation of piezoelectric phase, increase the crystallinity and promote the polarization level, inducing dramatically strengthened piezoelectric and output activity for PVDF. Additionally, the addition of MnO2 has the effect of significantly enhancing the mechanical property while slightly increasing dielectric constant of nanocomposites, which are advantageous to further harnessing the output enhancement. With an optimal loading of 1.0 wt% MnO2, the piezoelectric coefficient (d(33) approximate to 38 pC/N) an d correspondingly output response of hybrid films reached the peak. For instance, under the d(33) working mode, an output voltage of 3.2 V can be achieved in hybrid films while that of PVDF is only 1.7 V.

Electrospun polyvinylidene fluoride/polyacrylonitrile composite fibers: fabrication and characterization - Ke, Guizhen; Jin, Xinya; Hu, Haoxuan (IRANIAN POLYMER JOURNAL, 2020)
The purpose of this study is to make use of the advantages of both polyvinylidene fluoride (PVDF) and polyacrylonitrile (PAN) to fabricate a flexible electronic device. Polyvinylidene fluoride (PVDF)/polyacrylonitrile (PAN) composite fibrous mats with different blend ratios were fabricated using electrospinning. The effects of PVDF and PAN mass ratio on fiber morphology, chemical structure, thermal stability, and piezoelectric properties of the produced composite fibers were investigated by scanning electron microscopy (SEM), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), and piezoelectric tester. The SEM images showed that the PVDF/PAN composite nanofibers were fabricated successfully and fiber diameters increased with the increase of PVDF content. The FTIR and XRD analyses showed that both the alpha- and beta-crystal phases existed in PVDF/PAN composite fibers. The thermal stability of PVDF/PAN fibrous mats was less than that of nea t PVDF fibers. The piezoelectric properties of PVDF/PAN fibrous mats were significant and a function of PVDF content. The output voltage of PVDF/PAN fibrous mats increased from 1.2 to 5.0 V as PVDF content increased from 20 to 100%. The piezoelectric voltages of PVDF/PAN composite nanofibers also increased with the increase of impacting force. Tensile and contact angle testing indicated that the PVDF/PAN fibrous mats were more flexible and hydrophilic than neat PVDF membrane. PVDF/PAN nanocomposite fiber mats were observed suitable for potential application in flexible electronic devices.

Water flow drived piezo-photocatalytic flexible films: Bi-piezoelectric integration of ZnO nanorods and PVDF - Wu, Wen; Yin, Xin; Dai, Baoying; Kou, Jiahui; Ni, Yaru; Lu, Chunhua (APPLIED SURFACE SCIENCE, 2020)
Piezoelectric photocatalysis technology is widely employed to achieve excellent photocatalytic performance, as the internal electric field generated by the piezoelectric material can effectively accelerate the separation of photogenerated carriers. However, PVDF as a commonly used piezoelectric photocatalytic substrate, has a lower piezoelectric property, so it needs to be modified by other methods to improve its piezoelectric performance. In this work, piezoelectric semiconductor photocatalyst ZnO was selected to combine with PVDF film for a bipiezoelectric integration effect. Furthermore, in order to make the PVDF film generate a piezoelectric potential under a low-density energy field, ZnO powders exposed with different proportions of polar plane (1 0 0) plane were prepared separately and added into the films. The result shows that the ZnO-3@PVDF film with more extensive (1 0 0) polar plane exposure exhibits best piezoelectric effect for enhancing photocatalytic activity with magnet ic stirring, and the increase under water flow effect is 10 times that of ZnO-3@PDMS. Moreover, experimental results show that higher piezoelectric potential is more conducive to the improvement of photo-catalytic activity. This work developed a new piezo-photocatalytic flexible film for enhanced photocatalytic activity under low density flow water energy, and it offers great potential for eliminating environmental pollution.

Design of lead-free PVDF/CNT/BaTiO3 piezocomposites for sensing and energy harvesting: the role of polycrystallinity, nanoadditives, and anisotropy - Krishnaswamy, Jagdish A.; Buroni, Federico C.; Garcia-Macias, Enrique; Melnik, Roderick; Rodriguez-Tembleque, Luis; Saez, Andres (SMART MATERIALS AND STRUCTURES, 2020)
Lead-free piezoelectric composites with polymeric matrices offer a scalable and eco-friendly solution to sensing and energy harvesting applications. Piezoelectric polymers such as PVDF are particularly interesting because of the possibility to engineer the performance of these materials through addition of higher-performance piezoelectric inclusions and nanomaterials and to scalably manufacture such composites by emerging techniques such as 3D printing. This work makes two contributions, namely towards composite design and towards development of accurate effective property models. In the context of composite design, we evaluate the piezoelectric performance of PVDF modified by the addition of polycrystalline-BaTiO3 and multiwalled carbon nanotubes. Firstly, the addition of BaTiO3 dramatically improves the electric field within the composite offering significant advantages specially at low BaTiO3 concentrations. Secondly, the addition of carbon nanotubes to the matrix, particularly at h igher BaTiO3 loadings, leads to an order of magnitude increase in the piezoelectric flux generation. Further enhancement in the flux generation is also possible by tuning the polycrystallinity of the BaTiO3 inclusions. However, these behaviours are inclusion-driven and the piezoelectric behaviour of the matrix does not contribute to this improvement. Importantly, a small addition of BaTiO3 and CNT into the PVDF matrix, away from percolation, can simultaneously improve flux and electric field generation. In this part of the work, we assume an isotropic PVDF matrix. Given that PVDF is elastically anisotropic, the second aspect of this work is the development of an effective property model for CNT-modified PVDF, taking into account the elastic anisotropy of poled PVDF, to predict the elastic coefficients of CNT-modified PVDF matrices, thus undertaking a key step towards modelling anisotropic piezoelectric composites. We show that the anisotropy-based model makes similar predictions in the effective composite behaviour, indicating that in the case of PVDF-based piezocomposites, the anisotropy of the matrix does not significantly affect the piezoresponse.

Study of the optoelectronic and piezoelectric properties of ZrO2 doped PVDF from quantum chemistry calculations - Veved, Albert; Ejuh, Geh Wilson; Djongyang, Noel (CHINESE JOURNAL OF PHYSICS, 2020)
In this study, we have evaluated the optoelectronic and piezoelectric properties of doped PVDF. The electronic structures and the linear and non-linear optical properties of ZrO2-doped PVDF were calculated by adopting the LDA approximations for the exchange-correlation potential in the DFT method integrated in Gaussian 09. Optoelectronic parameters and ground state molecular geometry were calculated using B3LYP functional and LanL2DZ as the basis. We chose the calculation with the B3LYP functional because it is a relatively inexpensive and it is precise method to predict molecular structures, energies and frequencies. In this work, some optical parameters and constants such as refractive index, electrical susceptibility, dipole moment, average polarizability and hyperpolarizability, phase velocity have been calculated. Dielectric constants, ionization potentials, electronic affinities, electronegativities, hardness and flexibility were also calculated. Finally, the piezoelectric proper ties such as the piezoelectric coefficient and the pyroelectric coefficient are evaluated. The calculated electronic structures show that virgin PVDF, hybrid molecules PVDF/2ZrO2 and PVDF/3ZrO2 have an E-gap less than 3 eV. On the other hand, the hybrid PVDF/ZrO2 molecule is a good dielectric and therefore a good piezoelectric nanocomposite because its E gap is 5.89 eV greater than 3 eV. Finally, the results show that the hybrid molecules PVDF-2ZrO2 could have potential applications not only as piezoelectric materials but also as semiconductor components, nonlinear optical materials and possible building materials for molecular electronics and photonic devices.

Reseach progress of ferroelectric polymer nanocomposites with high energy storage density - ["Zhong-Hui Shen", "Yanda Jiang", "Bao-Wen Li", "Xin Zhang"] (Acta Physica Sinica, 2020)
Electrostatic capacitors based on dielectrics delivering an ultrahigh power density, low loss and high operating voltage, are widely used in energy storage devices for modern electronic and electrical systems. Dielectric polymers, especially ferroelectric polymers, are preferable for an energy storage medium in film capacitors due to their superiority in ultrahigh breakdown strength, low mass density, flexibility, and easy fabrication process. Ferroelectric polymer nanocomposites combining the advantageous properties of ferroelectric polymer matrix and high dielectric constant of ceramic fillers, show great potential applications in achieving superior energy storage performances and have aroused substantial academic interest. This review focuses on the recent research progress of high-energy-density ferroelectric polymer nanocomposites. First, the synthesis and properties of PVDF-based ferroelectric polymers are introduced. Second, the effects of nanofillers, composite structures and i nterfaces on the dielectric and energy storage properties of ferroelectric polymer nanocomposites are summarized. Third, the underline mechanism of dielectric and energy storage behaviors in ferroelectric nanocomposites are discussed in the aspect of phase-field simulation. Last, the existing challenges and future directions of ferroelectric polymer nanocomposites with high energy storage density are summarized and prospected.

Progress in lead-free piezoelectric nanofiller materials and related composite nanogenerator devices - ["Yong Zhang", "Hyunseung Kim", "Qing Wang", "Wook Jo", "Angus I. Kingon", "Seung-Hyun Kim", "Chang Kyu Jeong"] (Nanoscale Advances, 2020)
Current piezoelectric device systems need reduction in size and weight so electronic modules can be incorporated into many applications.

Research on gamma-ray irradiation-assisted synthesis of cross-linked polystyrene via bulk polymerization - Jie Zhao; Yunlong Hu; Jintao Li; six others (RG visible) (Journal of Radioanalytical and Nuclear Chemistry, 2020)
Cross-linked polystyrene was fabricated by bulk polymerization and gamma-ray irradiation.

Enhanced mechanical energy harvesting capability in sodium bismuth titanate based lead-free piezoelectric - Jian Wang; Zhonghui Shen; Zongliang Pan; six others (RG visible) (Journal of Alloys and Compounds, 2020)
Abstract The demand for high-performance lead-free piezoelectric materials towards mechanical energy harvesting has been driven by the continuous requirements of self-powered applications such as wireless sensor network systems and biomedical devices, etc. Herein, manganese-doped sodium bismuth titanate based lead-free ternary piezoelectric system 0.92(Na0.5Bi0.5)TiO3-0.04(K0.5Bi0.5)TiO3-0.04BaTiO3 (NBT-KBT-BT) was developed and the critical role of manganese on tailoring the microstructure and electrical properties was investigated. The highest piezoelectric coefficient (d33) of 140 pC/N with figure of merit (d33 × g33) of 1790 × 10−15 m2/N has been achieved. Both high open-circuit voltage of ∼12.2 V and power density of ∼0.37 μW/mm3 were obtained based on cantilever-type energy harvester. This work provides a promising paradigm for the development of high-performance mechanical energy harvesting devices by tailoring the composition of lead-free piezoelectric ceramics.

A flexible, ultra-highly sensitive and stable capacitive pressure sensor with convex microarrays for motion and health monitoring - Yaoxu Xiong, Youkang Shen, Lan Tian, Yougen Hu, Pengli Zhu, Rong Sun, Ching-Ping Wong (Nano Energy, 2020)

Ultra-Stretchable, durable and conductive hydrogel with hybrid double network as high performance strain sensor and stretchable triboelectric nanogenerator - Hongling Sun, Yi Zhao, Chunfeng Wang, Kangkang Zhou, Chao Yan, Guoqiang Zheng, Jiajia Huang, Kun Dai, Chuntai Liu, Changyu Shen (Nano Energy, 2020)

Engineered Microstructure Derived Hierarchical Deformation of Flexible Pressure Sensor Induces a Supersensitive Piezoresistive Property in Broad Pressure Range - Gang Li, Duo Chen, Chenglong Li, Wenxia Liu, Hong Liu (Advanced Science, 2020)
Abstract Fabricating flexible pressure sensors with high sensitivity in a broad pressure range is still a challenge. Herein, a flexible pressure sensor with engineered microstructures on polydimethylsiloxane (PDMS) film is designed. The high performance of the sensor derives from its unique pyramid‐wall‐grid microstructure (PWGM). A square array of dome‐topped pyramids and crossed strengthening walls on the film forms a multiheight hierarchical microstructure. Two pieces of PWGM flexible PDMS film, stacked face‐to‐face, form a piezoresistive sensor endowed with ultrahigh sensitivity across a very broad pressure range. The sensitivity of the device is as high as 383 665.9 and 269 662.9 kPa −1 in the pressure ranges 0–1.6 and 1.6–6 kPa, respectively. In the higher pressure range of 6.1–11 kPa, the sensitivity is 48 689.1 kPa −1 , and even in the very high pressure range of 11–56 kPa, it stays at 1266.8 kPa −1 . The pressure sensor possesses excellent bending and torsional strain detection properties, is mechanically durable, and has potential applications in wearable biosensing for healthcare. In addition, 2 × 2 and 4 × 4 sensor arrays are prepared and characterized, suggesting the possibility of manufacturing a flexible tactile sensor.

Strain-rate independent small-strain-sensor: Enhanced responsiveness of carbon black filled conductive rubber composites at slow deformation by using an ionic liquid - Jirawat Narongthong, Sven Wießner, Sakrit Hait, Chakrit Sirisinha, Klaus Werner Stöckelhuber (Composites Science and Technology, 2020)

Ultrathin, Biocompatible, and Flexible Pressure Sensor with a Wide Pressure Range and Its Biomedical Application - Yongrok Jeong, Jaeho Park, Jinwoo Lee, Kyuyoung Kim, Inkyu Park (ACS Sensors, 2020)

Platinum Nanozyme-Triggered Pressure-Based Immunoassay Using a Three-Dimensional Polypyrrole Foam-Based Flexible Pressure Sensor - Zhenzhong Yu, Guoneng Cai, Xiaolong Liu, Dianping Tang (ACS Applied Materials & Interfaces, 2020)

Tunable Pressure Sensor of f-Carbon Dot-Based Conductive Hydrogel with Electrical, Mechanical, and Shape Recovery for Monitoring Human Motion - Benny Ryplida, Insik In, Sung Young Park (ACS Applied Materials & Interfaces, 2020)

Flexible Sensor Arrays: Scalable Imprinting of Flexible Multiplexed Sensor Arrays with Distributed Piezoelectricity‐Enhanced Micropillars for Dynamic Tactile Sensing (Adv. Mater. Technol. 7/2020) - Xiaoliang Chen, Jinyou Shao, Hongmiao Tian, Xiangming Li, Chunhui Wang, Yongsong Luo, Sheng Li (Advanced Materials Technologies, 2020)

Soft and flexible sensor array using carbon black pillars for object recognition via pressure mapping - Kartik Yellapantula, Harish Devaraj, Mahtab Assadian, Logan Stuart, Cheng-Yao Lo, Wee Chen Gan, Kean Aw (Measurement, 2020)

LiF modified stable flexible PVDF-garnet hybrid electrolyte for high performance all-solid-state Li–S batteries - Sourav Bag, Chengtian Zhou, Patrick J. Kim, Vilas G. Pol, Venkataraman Thangadurai (Energy Storage Materials, 2020)

Giant energy storage density in PVDF with internal stress engineered polar nanostructures - Xintong Ren, Nan Meng, Han Zhang, Jiyue Wu, Isaac Abrahams, Haixue Yan, Emiliano Bilotti, Michael John Reece (Nano Energy, 2020)

Effect of Na+ MMT-ionic liquid synergy on electroactive, mechanical, dielectric and energy storage properties of transparent PVDF-based nanocomposites - Shixin Song, Shan Xia, Yan Liu, Xue Lv, Shulin Sun (Chemical Engineering Journal, 2020)

Microstructures, piezoelectric properties and energy harvesting performance of undoped (K0.5Na0.5)NbO3 lead-free ceramics fabricated via two-step sintering - G. Ye, J. Wade-Zhu, J. Zou, T. Zhang, T.W. Button, J. Binner (Journal of the European Ceramic Society, 2020)

Spontaneous relaxor to ferroelectric transition in lead-free relaxor piezoceramics and the role of point defects - Nitish Kumar, Xi Shi, Mark Hoffman (Journal of the European Ceramic Society, 2020)

Thermally-induced phase transformations in KNNS-BNKZ lead-free piezoceramics - J. Tangsritrakul, C.C. Tang, S.J. Day, D.A. Hall (Journal of the European Ceramic Society, 2020)

4 V room-temperature all-solid-state sodium battery enabled by a passivating cathode/hydroborate solid electrolyte interface - Ryo Asakura, David Reber, Léo Duchêne, SeyedHosein Payandeh, Arndt Remhof, Hans Hagemann, Corsin Battaglia (Energy & Environmental Science, 2020)
A self-passivating cathode/electrolyte interface achieves stable, room-temperature long-term cycling of 4 V-class Na3(VOPO4)2F|Na4(CB11H12)2(B12H12)|Na all-solid-state sodium batteries with the highest reported discharge cell voltage and cathode-based specific energy.

Polymer‐Clay Nanocomposite Solid‐State Electrolyte with Selective Cation Transport Boosting and Retarded Lithium Dendrite Formation - Young Min Jeon, Seulwoo Kim, Minhwan Lee, Won Bo Lee, Jong Hyeok Park (Advanced Energy Materials, 2020)
Abstract Commercialized lithium‐ion batteries (LIBs) with a liquid electrolyte have a high potential for combustion or explosion. The use of solid electrolytes in LIBs is a promising way to overcome the drawbacks of conventional liquid electrolyte‐based systems, but they generally have a lower ionic conductivity and lithium ion mobility. Here, a UV‐crosslinked composite polymer‐clay electrolyte (U‐CPCE) that is composed of a durable semi‐interpenetrating polymer network (semi‐IPN) ion transportive matrix (ETPTA/PVdF‐HFP) and 2D ultrathin clay nanosheets that are fabricated by a one‐step in situ UV curing method, are reported. The U‐CPCE exhibits robust and flexible properties with an ionic conductivity of more than 10 −3 S cm −1 at room temperature with the help of exfoliated clay nanosheets. As a result, the U‐CPCE‐based LIBs show an initial discharge capacity of 152 mAh g −1 (at 0.2 C for a LiCoO 2 half‐cell), which is comparable to that of conventional liquid electrolyte‐based cells . In addition, they show excellent cycling performance (96% capacity retention after 200 cycles at 0.5 C) due to a significantly enhanced Li + transference number ( t Li+ = 0.78) and inhibition of lithium dendrite formation on the lithium metal surface. Furthermore, a molecular dynamics (MD) study is conducted to elucidate the mechanism of improving ionic conductivity. The U‐CPCE design can offer opportunities for future all‐solid‐state Li‐ion batteries.

Effects of water‐based binders on electrochemical performance of manganese dioxide cathode in mild aqueous zinc batteries - Hee Jung Chang, Ismael A. Rodríguez‐Pérez, Matthew Fayette, Nathan Canfield, Huilin Pan, Daiwon Choi, Xiaolin Li, David Reed (Carbon Energy, 2020)
Abstract In the majority of rechargeable batteries including lithium‐ion batteries, polyvinylidene fluoride (PVdF) binders are the most commonly used binder for both anode and cathode. However, using PVdF binder requires the organic solvent of N ‐methyl‐2‐pyrrolidone which is expensive, volatile, combustible, toxic, and has poor recyclability. Therefore, switching to aqueous electrode processing routes with non‐toxic binders would provide a great leap forward towards the realization of ideally fully sustainable and environmentally friendly electrochemical energy storage devices. Various water‐soluble binders (aqueous binders) were characterized and compared to the performance of conventional PVdF. Our study demonstrates that the electrochemical performance of Zn/MnO 2 aqueous batteries is significantly improved by using sodium carboxymethyl cellulose (CMC) binder. In addition, CMC binders offer desirable adhesion, good wettability, homogeneous material distribution, and strong chemical stability at certain pH levels (3.5–5) without any decomposition for long‐cycle life.

Development of flexible Li‐ion batteries for flexible electronics - Yifan Zhao, Juchen Guo (InfoMat, 2020)
Abstract We provide a critical review on the recent development of flexible lithium‐ion batteries (FLIBs) for flexible electronic devices. The innovative designs of cell configuration for bendable and stretchable FLIBs, selection of active materials, and evaluation methods for FLIBs are discussed. The grand challenges for FLIBs are energy density and scale‐up fabrication as demonstrated in the review. Furthermore, the lack of quantitative evaluation methods for FLIBs' performance and nondestructive tools to probe the mechanical degradation may significantly hinder the development of FLIB technologies. Perspectives for future research directions, based on the current state of progress, are discussed. image

Assessment on the Use of High Capacity “Sn4P3”/NHC Composite Electrodes for Sodium‐Ion Batteries with Ether and Carbonate Electrolytes - Thangavelu Palaniselvam, Charan Mukundan, Ivana Hasa, A. L. Santhosha, Mustafa Göktaş, Hyein Moon, Mirco Ruttert, Richard Schmuch, Kilian Pollok, F. Langenhorst, Martin Winter, Stefano Passerini, Philipp Adelhelm (Advanced Functional Materials, 2020)
Abstract This work reports the facile synthesis of a Sn–P composite combined with nitrogen doped hard carbon (NHC) obtained by ball‐milling and its use as electrode material for sodium ion batteries (SIBs). The “Sn 4 P 3 ”/NHC electrode (with nominal composition “Sn 4 P 3 ”:NHC = 75:25 wt%) when coupled with a diglyme‐based electrolyte rather than the most commonly employed carbonate‐based systems, exhibits a reversible capacity of 550 mAh g electrode −1 at 50 mA g −1 and 440 mAh g electrode −1 over 500 cycles (83% capacity retention). Morphology and solid electrolyte interphase formation of cycled “Sn 4 P 3 ”/NHC electrodes is studied via electron microscopy and X‐ray photoelectron spectroscopy. The expansion of the electrode upon sodiation (300 mAh g electrode −1 ) is only about 12–14% as determined by in situ electrochemical dilatometry, giving a reasonable explanation for the excellent cycle life despite the conversion‐type storage mechanism. In situ X‐ray diffraction shows that th e discharge product is Na 15 Sn 4 . The formation of mostly amorphous Na 3 P is derived from the overall (electro)chemical reactions. Upon charge the formation of Sn is observed while amorphous P is derived, which are reversibly alloying with Na in the subsequent cycles. However, the formation of Sn 4 P 3 can be certainly excluded.

Copper Thiophosphate (Cu3PS4) as Electrode for Sodium‐Ion Batteries with Ether Electrolyte - Wolfgang Brehm, A. L. Santhosha, Zhenggang Zhang, Christof Neumann, Andrey Turchanin, Andréa Martin, Nicola Pinna, Martin Seyring, Markus Rettenmayr, Johannes Buchheim, Philipp Adelhelm (Advanced Functional Materials, 2020)
Abstract Lithium and sodium thiophosphates (and related compounds) have recently attracted attention because of their potential use as solid electrolytes in solid‐state batteries. These compounds, however, exhibit only limited stability in practice as they react with the electrodes. The decomposition products partially remain redox active hence leading to excess capacity. The redox activity of thiophosphates is explicitly used to act as electrode for sodium‐ion batteries. Copper thiophosphate (Cu 3 PS 4 ) is used as a model system. The storage behavior between 0.01 and 2.5 V versus Na + /Na is studied in half cells using different electrolytes with 1 m NaPF 6 in diglyme showing the best result. Cu 3 PS 4 shows highly reversible charge storage with capacities of about 580 mAh g −1 for more than 200 cycles @120 mA g −1 and about 450 mAh g −1 for 1400 cycles @1 A g −1 . The redox behavior is studied by operando X‐ray diffraction and X‐ray photoelectron spectroscopy. During initial sodiati on, Cu 3 PS 4 undergoes a conversion reaction including the formation of Cu and Na 2 S. During cycling, the redox activity seems dominated by sulfur. Interestingly, the capacity of Cu 3 PS 4 for lithium storage is smaller, leading to about 170 mAh g −1 after 200 cycles. The results demonstrate that thiophosphates can lead to reversible charge storage over several hundred cycles without any notable capacity decay.

Ultrathin RuRh Alloy Nanosheets Enable High-Performance Lithium-CO2 Battery - Yi Xing, Kai Wang, Na Li, Dong Su, Wing‐Tak Wong, Bolong Huang, Shaojun Guo (Matter, 2020)

Hybrid solid electrolyte enabled dendrite-free Li anodes for high-performance quasi-solid-state lithium-oxygen batteries - Jin Wang, Gang Huang, Jun‐Min Yan, Jinling Ma, Tong Liu, Miaomiao Shi, Yue Yu, Miaomiao Zhang, Jilin Tang, Xinbo Zhang (National Science Review, 2020)
Abstract The dendrite growth of Li anodes severely degrades the performance of lithium-oxygen (Li-O2) batteries. Recently, hybrid solid electrolyte (HSE) has been regarded as one of the most promising routes to tackle this problem. However, before this is realized, the HSE needs to simultaneously satisfy contradictory requirements of high modulus and even, flexible contact with Li anode, while ensuring uniform Li+ distribution. To tackle this complex dilemma, here, an HSE with rigid Li1.5Al0.5Ge1.5(PO4)3 (LAGP) core@ultrathin flexible poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) shell interface has been developed. The introduced large amount of nanometer-sized LAGP cores can not only act as structural enhancer to achieve high Young's modulus but can also construct Li+ diffusion network to homogenize Li+ distribution. The ultrathin flexible PVDF-HFP shell provides soft and stable contact between the rigid core and Li metal without affecting the Li+ distribution, meanwhile s uppressing the reduction of LAGP induced by direct contact with Li metal. Thanks to these advantages, this ingenious HSE with ultra-high Young's modulus of 25 GPa endows dendrite-free Li deposition even at a deposition capacity of 23.6 mAh. Moreover, with the successful inhibition of Li dendrites, the HSE-based quasi-solid-state Li-O2 battery delivers a long cycling stability of 146 cycles, which is more than three times that of gel polymer electrolyte-based Li-O2 battery. This new insight may serve as a starting point for further designing of HSE in Li-O2 batteries, and can also be extended to various battery systems such as sodium-oxygen batteries.

Crepe Cake Structured Layered Double Hydroxide/Sulfur/Graphene as a Positive Electrode Material for Li–S Batteries - Shengtang Liu, Xiuying Zhang, Shitao Wu, Xi Chen, Xiaojing Yang, Wenbo Yue, Jing Lü, Wuzong Zhou (ACS Nano, 2020)
Solving the polysulfide shuttle problem is one of the core challenges for the industrialization of lithium–sulfur batteries. In this work, a triphasic composite of LDH/sulfur/rGO (LDH: layered double hydroxide, rGO: reduced graphene oxide) with a crepe cake like structure is designed and fabricated as a positive electrode material for lithium–sulfur batteries. Sulfur nanoparticles are embedded in the interlayer space of the composite and thus are well protected physically via three-dimensional wrapping and chemically via strong interaction of LDH nanoflakes with lithium polysulfides, such as ionic bonds and S···H hydrogen bonds. In addition, the flexible lamellar structure of the composite with soft graphene layers can tolerate the volume expansion of sulfur during lithiation as well as facilitate ionic permeability and electron transport, which is favorable for the redox reactions of polysulfide. The present work sheds light on the future development and industrialization of lithium–s ulfur batteries.

3D microstructure design of lithium-ion battery electrodes assisted by X-ray nano-computed tomography and modelling - Xuekun Lu, Antonio Bertei, Donal P. Finegan, Chun Tan, Sohrab R. Daemi, Julia S. Weaving, Kieran O’Regan, Thomas M. M. Heenan, Gareth Hinds, Emma Kendrick, Dan J. L. Brett, Paul R. Shearing (Nature Communications, 2020)
Driving range and fast charge capability of electric vehicles are heavily dependent on the 3D microstructure of lithium-ion batteries (LiBs) and substantial fundamental research is required to optimise electrode design for specific operating conditions. Here we have developed a full microstructure-resolved 3D model using a novel X-ray nano-computed tomography (CT) dual-scan superimposition technique that captures features of the carbon-binder domain. This elucidates how LiB performance is markedly affected by microstructural heterogeneities, particularly under high rate conditions. The elongated shape and wide size distribution of the active particles not only affect the lithium-ion transport but also lead to a heterogeneous current distribution and non-uniform lithiation between particles and along the through-thickness direction. Building on these insights, we propose and compare potential graded-microstructure designs for next-generation battery electrodes. To guide manufacturing of electrode architectures, in-situ X-ray CT is shown to reliably reveal the porosity and tortuosity changes with incremental calendering steps.

Mechanical rolling formation of interpenetrated lithium metal/lithium tin alloy foil for ultrahigh-rate battery anode - Mintao Wan, Sujin Kang, Li Wang, Hyun‐Wook Lee, Guangyuan Zheng, Yi Cui, Yongming Sun (Nature Communications, 2020)
Abstract To achieve good rate capability of lithium metal anodes for high-energy-density batteries, one fundamental challenge is the slow lithium diffusion at the interface. Here we report an interpenetrated, three-dimensional lithium metal/lithium tin alloy nanocomposite foil realized by a simple calendering and folding process of lithium and tin foils, and spontaneous alloying reactions. The strong affinity between the metallic lithium and lithium tin alloy as mixed electronic and ionic conducting networks, and their abundant interfaces enable ultrafast charger diffusion across the entire electrode. We demonstrate that a lithium/lithium tin alloy foil electrode sustains stable lithium stripping/plating under 30 mA cm −2 and 5 mAh cm −2 with a very low overpotential of 20 mV for 200 cycles in a commercial carbonate electrolyte. Cycled under 6 C (6.6 mA cm −2 ), a 1.0 mAh cm −2 LiNi 0.6 Co 0.2 Mn 0.2 O 2 electrode maintains a substantial 74% of its capacity by pairing with such anode.

Metal chloride perovskite thin film based interfacial layer for shielding lithium metal from liquid electrolyte - Yi‐Chen Yin, Qian Wang, Jing-Tian Yang, Feng Li, Guozhen Zhang, Chenhui Jiang, Hongsheng Mo, Jisong Yao, Kunhua Wang, Fei Zhou, Huanxin Ju, Hong‐Bin Yao (Nature Communications, 2020)
Abstract Fabricating a robust interfacial layer on the lithium metal anode to isolate it from liquid electrolyte is vital to restrain the rapid degradation of a lithium metal battery. Here, we report that the solution-processed metal chloride perovskite thin film can be coated onto the lithium metal surface as a robust interfacial layer to shield the lithium metal from liquid electrolyte. Via phase analysis and density functional theory calculations, we demonstrate that the perovskite layer can allow fast lithium ion shuttle under a low energy barrier of 0.45 eV without the collapse of framework. Such perovskite modification can realize stable cycling of LiCoO 2 |Li cells with an areal capacity of 2.8 mAh cm −2 using thin lithium metal foil (50 μm) and limited electrolyte (20 μl mAh −1 ) for over 100 cycles at 0.5 C. The metal chloride perovskite protection strategy could open a promising avenue for advanced lithium metal batteries.

Depth-dependent valence stratification driven by oxygen redox in lithium-rich layered oxide - Jin Zhang, Qinchao Wang, Shaofeng Li, Zhisen Jiang, Sha Tan, Xuelong Wang, Kai Zhang, Qingxi Yuan, Sang‐Jun Lee, Charles J. Titus, K. D. Irwin, Dennis Nordlund, Jun‐Sik Lee, P. Pianetta, Xiqian Yu, Xianghui Xiao, Xiao‐Qing Yang, Enyuan Hu, Yijin Liu (Nature Communications, 2020)
Abstract Lithium-rich nickel-manganese-cobalt (LirNMC) layered material is a promising cathode for lithium-ion batteries thanks to its large energy density enabled by coexisting cation and anion redox activities. It however suffers from a voltage decay upon cycling, urging for an in-depth understanding of the particle-level structure and chemical complexity. In this work, we investigate the Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 particles morphologically, compositionally, and chemically in three-dimensions. While the composition is generally uniform throughout the particle, the charging induces a strong depth dependency in transition metal valence. Such a valence stratification phenomenon is attributed to the nature of oxygen redox which is very likely mostly associated with Mn. The depth-dependent chemistry could be modulated by the particles’ core-multi-shell morphology, suggesting a structural-chemical interplay. These findings highlight the possibility of introducing a chemical gradien t to address the oxygen-loss-induced voltage fade in LirNMC layered materials.

Electrolyte Oxidation Pathways in Lithium-Ion Batteries - Bernardine L. D. Rinkel, David S. Hall, Israel Temprano, Clare P. Grey (Journal of the American Chemical Society, 2020)
The mitigation of decomposition reactions of lithium-ion battery electrolyte solutions is of critical importance in controlling device lifetime and performance. However, due to the complexity of the system, exacerbated by the diverse set of electrolyte compositions, electrode materials, and operating parameters, a clear understanding of the key chemical mechanisms remains elusive. In this work, operando pressure measurements, solution NMR, and electrochemical methods were combined to study electrolyte oxidation and reduction at multiple cell voltages. Two-compartment LiCoO2/Li cells were cycled with a lithium-ion conducting glass–ceramic separator so that the species formed at each electrode could be identified separately and further reactions of these species at the opposite electrode prevented. One principal finding is that chemical oxidation (with an onset voltage of ∼4.7 V vs Li/Li+ for LiCoO2), rather than electrochemical reaction, is the dominant decomposition process at the posi tive electrode surface in this system. This is ascribed to the well-known release of reactive oxygen at higher states-of-charge, indicating that reactions of the electrolyte at the positive electrode are intrinsically linked to surface reactivity of the active material. Soluble electrolyte decomposition products formed at both electrodes are characterized, and a detailed reaction scheme is constructed to rationalize the formation of the observed species. The insights on electrolyte decomposition through reactions with reactive oxygen species identified through this work have a direct impact on understanding and mitigating degradation in high-voltage/higher-energy-density LiCoO2-based cells, and more generally for cells containing nickel-containing cathode materials (e.g., LiNixMnyCozO2; NMCs), as they lose oxygen at lower operating voltages.

Atomic-scale tuned interface of nickel-rich cathode for enhanced electrochemical performance in lithium-ion batteries - Yongqiang Liu, Xin Wang, Jiyu Cai, Xiaoxiao Han, Dongsheng Geng, Jianlin Li, Xiangbo Meng (Journal of Material Science and Technology, 2020)

Safer Lithium‐Ion Batteries from the Separator Aspect: Development and Future Perspectives - Zhifang Liu, Yingjun Jiang, Qiaomei Hu, Songtao Guo, Le Yu, Qi Li, Qing Liu, Xianluo Hu (Energy & environment materials, 2020)
With the rapid development of lithium‐ion batteries (LIBs), safety problems are the great obstacles that restrict large‐scale applications of LIBs, especially for the high‐energy‐density electric vehicle industry. Developing component materials (e.g., cathode, anode, electrolyte, and separator) with high thermal stability and intrinsic safety is the ultimate solution to improve the safety of LIBs. Separators are crucial components that do not directly participate in electrochemical reactions during charging/discharging processes, but play a vital role in determining the electrochemical performance and safety of LIBs. In this review, the recent advances on traditional separators modified with ceramic materials and multifunctional separators ranging from the prevention of the thermal runaway to the flame retardant are summarized. The component–structure–performance relationship of separators and their effect on the comprehensive performance of LIBs are discussed in detail. Furthermore, t he research challenges and future directions toward the advancement in separators for high‐safety LIBs are also proposed.

Expansion-tolerant architectures for stable cycling of ultrahigh-loading sulfur cathodes in lithium-sulfur batteries - Mahdokht Shaibani, Meysam Sharifzadeh Mirshekarloo, Ruhani Singh, Christopher D. Easton, M. C. Dilusha Cooray, Nicolas Eshraghi, Thomas Abendroth, Susanne Dörfler, Holger Althues, Stefan Kaskel, Anthony F. Hollenkamp, Matthew R. Hill, Mainak Majumder (Science Advances, 2020)
) capacities. The cells are stable for more than 200 cycles, unprecedented in such thick cathodes, with Coulombic efficiency above 99%.

Comparison of the effects of incineration, vacuum pyrolysis and dynamic pyrolysis on the composition of NMC-lithium battery cathode-material production scraps and separation of the current collector - Gabriele Lombardo, Burçak Ebin, Britt‐Marie Steenari, Mahmood Alemrajabi, Ingrid Karlsson, Martina Petraniková (Resources Conservation and Recycling, 2020)
The rising demand for lithium batteries is challenging battery producers to increase their production. This is causing an accumulation of production scrap which must be treated to allow re-utilization of cathode material in production. Several industrial lithium battery recycling processes use thermal pre-treatment in an oxidative or inert atmosphere, or in a vacuum, to separate the battery components and remove organic material. However, a comparison of the effects of incineration, dynamic pyrolysis (under a constant flow of inert gas), and pyrolysis under vacuum on the microstructure and composition of scrap cathode material has not been explored. Scrap cathodes, with active material based on Li(NixMnyCoz)Oj, were subjected to incineration, dynamic pyrolysis, and pyrolysis under vacuum at 450˚, 550˚, and 650°C for 30, 60, 90, and 150 min to determine the best approach to cathode material recovery. While the incineration did not cause any chemical transformation of cathode material, u nder pyrolysis conditions the organic components in the cathodes triggered carbothermic reduction of the active material, yielding Co3O4, NiO, Mn3O4, and Li2CO3 as products. In the gas by-products, formed from the decomposition of the organic material, CO, CO2, and HF were determined. The decomposition especially of the binder in polyvinylidene fluoride (PVDF) facilitated the separation of the active material from the current collector by mechanical treatment. By subsequent ball milling, the best technique to recover cathode material is the incineration at a temperature higher than 550˚ C and below 650˚ C for at least 90 min, with >95% of recovered active material.

Aqueous Ni-rich-cathode dispersions processed with phosphoric acid for lithium-ion batteries with ultra-thick electrodes - Alexander Kukay, Ritu Sahore, Anand Parejiya, W. Blake Hawley, Jianlin Li, David L. Wood (Journal of Colloid and Interface Science, 2020)

MoS2 Nanosheets Sensitized with Quantum Dots for Room-Temperature Gas Sensors - Jing‐yao Liu, Zhixiang Hu, Yuzhu Zhang, Hua‐Yao Li, Naibo Gao, Zhilai Tian, Licheng Zhou, Baohui Zhang, Jiang Tang, Jianbing Zhang, Fei Yi, Huan Liu (Nano-Micro Letters, 2020)
Abstract The Internet of things for environment monitoring requires high performance with low power-consumption gas sensors which could be easily integrated into large-scale sensor network. While semiconductor gas sensors have many advantages such as excellent sensitivity and low cost, their application is limited by their high operating temperature. Two-dimensional (2D) layered materials, typically molybdenum disulfide (MoS 2 ) nanosheets, are emerging as promising gas-sensing materials candidates owing to their abundant edge sites and high in-plane carrier mobility. This work aims to overcome the sluggish and weak response as well as incomplete recovery of MoS 2 gas sensors at room temperature by sensitizing MoS 2 nanosheets with PbS quantum dots (QDs). The huge amount of surface dangling bonds of QDs enables them to be ideal receptors for gas molecules. The sensitized MoS 2 gas sensor exhibited fast and recoverable response when operated at room temperature, and the limit of NO 2 de tection was estimated to be 94 ppb. The strategy of sensitizing 2D nanosheets with sensitive QD receptors may enhance receptor and transducer functions as well as the utility factor that determine the sensor performance, offering a powerful new degree of freedom to the surface and interface engineering of semiconductor gas sensors.

Parallel Nanoimprint Forming of One-Dimensional Chiral Semiconductor for Strain-Engineered Optical Properties - Yixiu Wang, S. Jin, Qingxiao Wang, Min Wu, Shukai Yao, Peilin Liao, Moon J. Kim, Gary J. Cheng, Wenzhuo Wu (Nano-Micro Letters, 2020)
The low-dimensional, highly anisotropic geometries, and superior mechanical properties of one-dimensional (1D) nanomaterials allow the exquisite strain engineering with a broad tunability inaccessible to bulk or thin-film materials. Such capability enables unprecedented possibilities for probing intriguing physics and materials science in the 1D limit. Among the techniques for introducing controlled strains in 1D materials, nanoimprinting with embossed substrates attracts increased attention due to its capability to parallelly form nanomaterials into wrinkled structures with controlled periodicities, amplitudes, orientations at large scale with nanoscale resolutions. Here, we systematically investigated the strain-engineered anisotropic optical properties in Te nanowires through introducing a controlled strain field using a resist-free thermally assisted nanoimprinting process. The magnitude of induced strains can be tuned by adjusting the imprinting pressure, the nanowire diameter, an d the patterns on the substrates. The observed Raman spectra from the chiral-chain lattice of 1D Te reveal the strong lattice vibration response under the strain. Our results suggest the potential of 1D Te as a promising candidate for flexible electronics, deformable optoelectronics, and wearable sensors. The experimental platform can also enable the exquisite mechanical control in other nanomaterials using substrate-induced, on-demand, and controlled strains.

Photonic Fractal Metamaterials: A Metal–Semiconductor Platform with Enhanced Volatile‐Compound Sensing Performance - Zelio Fusco, Mohsen Rahmani, Thành Trần‐Phú, Chiara Ricci, Alexander Kiy, P. Kluth, Enrico Della Gaspera, Nunzio Motta, Dragomir N. Neshev, Antonio Tricoli (Advanced Materials, 2020)
Abstract Advance of photonics media is restrained by the lack of structuring techniques for the 3D fabrication of active materials with long‐range periodicity. A methodology is reported for the engineering of tunable resonant photonic media with thickness exceeding the plasmonic near‐field enhancement region by more than two orders of magnitude. The media architecture consists of a stochastically ordered distribution of plasmonic nanocrystals in a fractal scaffold of high‐index semiconductors. This plasmonic‐semiconductor fractal media supports the propagation of surface plasmons with drastically enhanced intensity over multiple length scales, overcoming the 2D limitations of established metasurface technologies. The fractal media are used for the fabrication of plasmonic optical gas sensors, achieving a limit of detection of 0.01 vol% at room temperature and sensitivity up to 1.9 nm vol% −1 , demonstrating almost a fivefold increase with respect to an optimized planar geometry. Benefi cially to their implementation, the self‐assembly mechanism of this fractal architecture allows fabrication of micrometer‐thick media over surfaces of several square centimeters in a few seconds. The designable optical features and intrinsic scalability of these photonic fractal metamaterials provide ample opportunities for applications, bridging across transformation optics, sensing, and light harvesting.

Thermally drawn advanced functional fibers: New frontier of flexible electronics - Wei Yan, Chaoqun Dong, Yuanzhuo Xiang, Shan Jiang, Andreas Leber, Gabriel Loke, Wenxin Xu, Chong Hou, Shifeng Zhou, Min Chen, Run Hu, Perry Ping Shum, Lei Wei, Xiaoting Jia, Fabien Sorin, Xiaoming Tao, Guangming Tao (Materials Today, 2020)
Electronic devices are evolving from rigid devices into flexible and stretchable structures, enabling a seamless integration of electronics into our everyday lives. The integration of a variety of electronic materials within thermal-drawn fibers has emerged as a versatile platform for the fabrication of advanced functional fiber electronics. This approach exploits the thermal drawing of a macroscopic preform, where functional materials or prefabricated devices are arranged at a prescribed position, yielding kilometers of electronic fibers with a sophisticated architecture and complex functionalities in a very simple and scalable manner. A single strand of fiber that incorporates materials with disparate electronic, optoelectronics, thermomechanical, rheological and acoustic properties can see objects, hear sound, sense stimuli, communicate, store and convert energy, modulate temperature, monitor health and dissect brains. Integrating these electronic fibers into fabrics, ancient yet la rgely underdeveloped forms, is setting a stage for fabrics to be the next frontier in computation and Artificial Intelligence. Here, we critically review the development of thermally drawn fiber electronics and highlight their unique opportunities in communications, sensing, energy, artificial muscles, 3-D printing, healthcare, neuroscience as well as in-fiber materials fundamental research. We conclude some perspectives for realizing an analogue of “Moore’s law” in fibers and fabrics and the remaining challenges for future research.

Flexible and stretchable metal oxide nanofiber networks for multimodal and monolithically integrated wearable electronics - Binghao Wang, Anish Thukral, Zhaoqian Xie, Limei Liu, Xinan Zhang, Wei Huang, Xinge Yu, Cunjiang Yu, Tobin J. Marks, Antonio Facchetti (Nature Communications, 2020)
Fiber-based electronics enabling lightweight and mechanically flexible/stretchable functions are desirable for numerous e-textile/e-skin optoelectronic applications. These wearable devices require low-cost manufacturing, high reliability, multifunctionality and long-term stability. Here, we report the preparation of representative classes of 3D-inorganic nanofiber network (FN) films by a blow-spinning technique, including semiconducting indium-gallium-zinc oxide (IGZO) and copper oxide, as well as conducting indium-tin oxide and copper metal. Specifically, thin-film transistors based on IGZO FN exhibit negligible performance degradation after one thousand bending cycles and exceptional room-temperature gas sensing performance. Owing to their great stretchability, these metal oxide FNs can be laminated/embedded on/into elastomers, yielding multifunctional single-sensing resistors as well as fully monolithically integrated e-skin devices. These can detect and differentiate multiple stimu li including analytes, light, strain, pressure, temperature, humidity, body movement, and respiratory functions. All of these FN-based devices exhibit excellent sensitivity, response time, and detection limits, making them promising candidates for versatile wearable electronics.

Understanding coordination reaction for producing stable electrode with various low work functions - Hirohiko Fukagawa, Kazuma Suzuki, Hirokazu Ito, Kaito Inagaki, Tsubasa Sasaki, Taku Oono, Munehiro Hasegawa, Katsuyuki Morii, Takahisa Shimizu (Nature Communications, 2020)
The realisation of a cathode with various work functions (WFs) is required to maximise the potential of organic semiconductors that have various electron affinities. However, the barrier-free contact for electrons could only be achieved by using reactive materials, which significantly reduce the environmental stability of organic devices. We show that a stable electrode with various WFs can be produced by utilising the coordination reaction between several phenanthroline derivatives and the electrode. Although the low WF of the electrode realised by using reactive materials is specific to the material, the WF of the phenanthroline-modified electrode is tunable depending on the amount of electron transfer associated with the coordination reaction. A phenanthroline-modified electrode that has a higher electron injection efficiency than lithium fluoride has been demonstrated. The observation of various WFs induced by the coordination reaction affords strategic perspectives on the developm ent of stable cathodes unique to organic electronics.

Toward three-dimensional hybrid inorganic/organic optoelectronics based on GaN/oCVD-PEDOT structures - Linus Krieg, Florian Meierhofer, Sascha Gorny, Stefan Leis, Daniel Splith, Zhipeng Zhang, Holger von Wenckstern, Marius Grundmann, Xiaoxue Wang, Jana Hartmann, Christoph Margenfeld, Irene Manglano Clavero, Adrian Avramescu, Tilman Schimpke, Dominik Scholz, Hans‐Jürgen Lugauer, Martin Straßburg, Jörgen Jungclaus, Steffen Bornemann, Hendrik Spende (Nature Communications, 2020)
The combination of inorganic semiconductors with organic thin films promises new strategies for the realization of complex hybrid optoelectronic devices. Oxidative chemical vapor deposition (oCVD) of conductive polymers offers a flexible and scalable path towards high-quality three-dimensional inorganic/organic optoelectronic structures. Here, hole-conductive poly(3,4-ethylenedioxythiophene) (PEDOT) grown by oxidative chemical vapor deposition is used to fabricate transparent and conformal wrap-around p-type contacts on three-dimensional microLEDs with large aspect ratios, a yet unsolved challenge in three-dimensional gallium nitride technology. The electrical characteristics of two-dimensional reference structures confirm the quasi-metallic state of the polymer, show high rectification ratios, and exhibit excellent thermal and temporal stability. We analyze the electroluminescence from a three-dimensional hybrid microrod/polymer LED array and demonstrate its improved optical propertie s compared with a purely inorganic microrod LED. The findings highlight a way towards the fabrication of hybrid three-dimensional optoelectronics on the sub-micron scale.

Recent advances in hybrid perovskite nanogenerators - Ran Ding, Man‐Chung Wong, Jianhua Hao (EcoMat, 2020)
Abstract Hybrid organic‐inorganic halide perovskites have attracted massive attention during the last several years because of their promising properties for high‐performance electronic and optoelectronic devices. The intriguing ferroic nature of hybrid perovskites, especially ferroelectric and piezoelectric properties, bring new opportunities for mechanical energy harvesting applications. They are also introduced as triboelectric materials coupling with their remarkable dielectric and electrical features. This mini review presents a concise overview of the recent progress on hybrid perovskite nanogenerators, including piezoelectric nanogenerators and triboelectric nanogenerators. Different dimensional perovskites with prominent ferroelectric and piezoelectric properties are discussed in detail. Lastly, we provide a brief outlook for the future development of self‐powered wearable electronics based on hybrid perovskites. image

Semiconductor photoelectroanalysis and photobioelectroanalysis: A perspective - Sirlon F. Blaskievicz, Lúcia H. Mascaro, Yuanzhu Zhao, Frank Marken (TrAC Trends in Analytical Chemistry, 2020)

Micron Thick Colloidal Quantum Dot Solids - James Z. Fan, Maral Vafaie, Koen Bertens, Mykhailo Sytnyk, João M. Pina, Laxmi Kishore Sagar, Olivier Ouellette, Andrew H. Proppe, Armin Sedighian Rasouli, Yajun Gao, Se‐Woong Baek, Bin Chen, Frédéric Laquai, Sjoerd Hoogland, F. Pelayo Garcı́a de Arquer, Wolfgang Heiß, Edward H. Sargent (Nano Letters, 2020)
Shortwave infrared colloidal quantum dots (SWIR-CQDs) are semiconductors capable of harvesting across the AM1.5G solar spectrum. Today’s SWIR-CQD solar cells rely on spin-coating; however, these films exhibit cracking once thickness exceeds ∼500 nm. We posited that a blade-coating strategy could enable thick QD films. We developed a ligand exchange with an additional resolvation step that enabled the dispersion of SWIR-CQDs. We then engineered a quaternary ink that combined high-viscosity solvents with short QD stabilizing ligands. This ink, blade-coated over a mild heating bed, formed micron-thick SWIR-CQD films. These SWIR-CQD solar cells achieved short-circuit current densities (Jsc) that reach 39 mA cm–2, corresponding to the harvest of 60% of total photons incident under AM1.5G illumination. External quantum efficiency measurements reveal both the first exciton peak and the closest Fabry–Perot resonance peak reaching approximately 80%—this is the highest unbiased EQE reported beyo nd 1400 nm in a solution-processed semiconductor.

Flexible high-performance graphene hybrid photodetectors functionalized with gold nanostars and perovskites - Yoon Ho Lee, Seung‐Young Park, Yousang Won, Jungho Mun, Jae Hwan Ha, Jeong Hun Lee, Sang Hyuk Lee, Jongmin Park, Jeonghee Yeom, Junsuk Rho, Hyunhyub Ko, Joon Hak Oh (NPG Asia Materials, 2020)
Abstract Hybrid materials in optoelectronic devices can provide synergistic effects that complementarily enhance the properties of each component. Here, flexible high-performance graphene hybrid photodetectors (PDs) are developed by introducing gold nanostars (GNSs) and perovskites for strong light trapping with hot electron transfer and efficient light harvesting characteristics, respectively. While pristine graphene PDs do not exhibit discernible photodetection properties due to the very low photon absorption and ultrafast charge carrier recombination, graphene PDs functionalized with GNSs and a densely covered perovskite layer exhibit outstanding photoresponsive properties with a photoresponsivity ( R ) of 5.90 × 10 4 A W −1 and a specific detectivity of 1.31 × 10 13 Jones, the highest values among those reported for perovskite-functionalized graphene PDs thus far. Moreover, we fabricated a flexible 10 × 10 PD array that shows well-resolved spatiotemporal mapping of light signals wi th excellent operational and mechanical stabilities at a bending radius down to 3 mm and in repeated bending tests for over 1000 cycles. Comprehensive analyses using finite-difference time-domain (FDTD) theoretical calculations, scanning near-field optical microscopy, and photoluminescence mapping reveal the effective light trapping effect of GNSs and the charge carrier transfer between the perovskite and graphene. This work provides a new design platform for flexible and high-performance photodetection systems.

Engineering of SnO2–Graphene Oxide Nanoheterojunctions for Selective Room-Temperature Chemical Sensing and Optoelectronic Devices - Eleonora Pargoletti, U.H. Hossain, Iolanda Di Bernardo, Hongjun Chen, Thành Trần‐Phú, Gian Luca Chiarello, Josh Lipton‐Duffin, V. Pifferi, Antonio Tricoli, G. Cappelletti (ACS Applied Materials & Interfaces, 2020)
The development of high-performing sensing materials, able to detect ppb-trace concentrations of volatile organic compounds (VOCs) at low temperatures, is required for the development of next-generation miniaturized wireless sensors. Here, we present the engineering of selective room-temperature (RT) chemical sensors, comprising highly porous tin dioxide (SnO 2 )-graphene oxide (GO) nanoheterojunction layouts. The optoelectronic and chemical properties of these highly porous (>90%) p-n heterojunctions were systematically investigated in terms of composition and morphologies. Optimized SnO 2 -GO layouts demonstrate significant potential as both visible-blind photodetectors and selective RT chemical sensors. Notably, a low GO content results in an excellent UV light responsivity (400 A W -1 ), with short rise and decay times, and RT high chemical sensitivity with selective detection of VOCs such as ethanol down to 100 ppb. In contrast, a high concentration of GO drastically decreases the RT response to ethanol and results in good selectivity to ethylbenzene. The feasibility of tuning the chemical selectivity of sensor response by engineering the relative amount of GO and SnO 2 is a promising feature that may guide the future development of miniaturized solid-state gas sensors. Furthermore, the excellent optoelectronic properties of these SnO 2 -GO nanoheterojunctions may find applications in various other areas such as optoelectronic devices and (photo)electrocatalysis.

Recent advances on hybrid integration of 2D materials on integrated optics platforms - Qijie Ma, Guanghui Ren, Arnan Mitchell, Jian Zhen Ou (Nanophotonics, 2020)
Abstract The burgeoning research into two‐dimensional (2D) materials opens a door to novel photonic and optoelectronic devices utilizing their fascinating electronic and photonic properties in thin‐layered architectures. The hybrid integration of 2D materials onto integrated optics platforms thus becomes a potential solution to tackle the bottlenecks of traditional optoelectronic devices. In this paper, we present the recent advances of hybrid integration of a wide range of 2D materials on integrated optics platforms for developing high‐performance photodetectors, modulators, lasers, and nonlinear optics. Such hybrid integration enables fully functional on‐chip devices to be readily accessible researchers and technology developers, becoming a potential candidate for next‐generation photonics and optoelectronics industries.

High‐performance monolayer MoS 2 photodetector enabled by oxide stress liner using scalable chemical vapor growth method - Zhiwen Li, Jing Wu, Cong Wang, Han Zhang, Wenjie Yu, Youming Lu, Xinke Liu (Nanophotonics, 2020)
Abstract MoS 2 , as a typical representative of two‐dimensional semiconductors, has been explored extensively in applications of optoelectronic devices because of its adjustable bandgap. However, to date, the performance of the fabricated photodetectors has been very sensitive to the surrounding environment owing to the large surface‐to‐volume ratio. In this work, we report on large‐scale, high‐performance monolayer MoS 2 photodetectors covered with a 3‐nm Al 2 O 3 layer grown by atomic layer deposition. In comparison with the device without the Al 2 O 3 stress liner, both the photocurrent and responsivity are improved by over 10 times under 460‐nm light illumination, which is due to the tensile strain induced by the Al 2 O 3 layer. Further characterization demonstrated state‐of‐the‐art performance of the device with a responsivity of 16.103 A W −1 , gain of 191.80, NEP of 7.96 × 10 −15 W Hz −1/2 , and detectivity of 2.73 × 10 10 Jones. Meanwhile, the response rise time of the photodet ector also reduced greatly because of the increased electron mobility and reduced surface defects due to the Al 2 O 3 stress liner. Our results demonstrate the potential application of large‐scale strained monolayer MoS 2 photodetectors in next‐generation imaging systems.

Epitaxial aluminum plasmonics covering full visible spectrum - Chang‐Wei Cheng, Soniya S. Raja, Ching‐Wen Chang, Xinquan Zhang, Po‐Yen Liu, Yi‐Hsien Lee, Chih‐Kang Shih, Shangjr Gwo (Nanophotonics, 2020)
Abstract Aluminum has attracted a great deal of attention as an alternative plasmonic material to silver and gold because of its natural abundance on Earth, material stability, unique spectral capability in the ultraviolet spectral region, and complementary metal‐oxide‐semiconductor compatibility. Surprisingly, in some recent studies, aluminum has been reported to outperform silver in the visible range due to its superior surface and interface properties. Here, we demonstrate excellent structural and optical properties measured for aluminum epitaxial films grown on sapphire substrates by molecular‐beam epitaxy under ultrahigh vacuum growth conditions. Using the epitaxial growth technique, distinct advantages can be achieved for plasmonic applications, including high‐fidelity nanofabrication and wafer‐scale system integration. Moreover, the aluminum film thickness is controllable down to a few atomic monolayers, allowing for plasmonic ultrathin layer devices. Two kinds of aluminum plasm onic applications are reported here, including precisely engineered plasmonic substrates for surface‐enhanced Raman spectroscopy and high‐quality‐factor plasmonic surface lattices based on standing localized surface plasmons and propagating surface plasmon polaritons, respectively, in the entire visible spectrum (400–700 nm).

Solution‐Processable 2D Materials Applied in Light‐Emitting Diodes and Solar Cells - Antonio Gaetano Ricciardulli, Paul W. M. Blom (Advanced Materials Technologies, 2020)
Abstract The last decades have witnessed a remarkable scientific progress in the field of organic and perovskite optoelectronics. Two‐dimensional (2D) materials are an attractive building block for next‐generation devices, thanks to their unique physical, optical, and electric characteristics including atomically thin bodies, high transmittance, ultralight weight, and tunable band structures. The state‐of‐the‐art optoelectronic devices utilizing 2D materials mainly rely on 2D thin films grown by chemical vapor deposition. Although good device performances have been demonstrated, a huge gap between fundamental studies and practical applications remains, because of the high cost and troublesome transfer/restacking processes. Therefore, flexible and transparent light‐emitting diodes (LEDs) and solar cells (SCs) containing solution‐processed 2D materials from top‐down exfoliation methods have recently emerged as promising candidates for future light conversion and emission devices. They co mbine ease of processing, tailorable optoelectronic features, facile integration with complementary layers, compatibility with arbitrary substrates, and enhanced performances. In addition, the latest processing techniques (such as ink‐jet printing, spray coating) also offer the opportunity for the scaled‐up fabrication of square‐meter‐scale low‐cost device systems. Recent advances, challenges, and future perspectives of solution‐processed 2D materials for usage in emerging LEDs and SCs applications are discussed here.

Opto-electronic coupling in semiconductors: towards ultrasensitive pressure sensing - Thanh Nguyen, Thanh Nguyen, Toan Dinh, Hoang‐Phuong Phan, Tuan-Khoa Nguyen, Tuan-Khoa Nguyen, Abu Riduan Md Foisal, Nam‐Trung Nguyen, Dzung Viet Dao (Journal of Materials Chemistry C, 2020)
A novel concept of opto-electronic coupling in semiconductor heterojunctions for pressure sensing is proposed. By using non-uniform illumination of visible light coupling with tuning current, performance of the pressure sensor is enormously enhanced.

Anisotropic circular photogalvanic effect in colloidal tin sulfide nanosheets - Mohammad Mehdi Ramin Moayed, Fu Li, Philip Beck, Jan‐Christian Schober, Christian Klinke (Nanoscale, 2020)
Tin sulfide promises very interesting properties such as a high optical absorption coefficient and a small band gap, while being less toxic compared to other metal chalcogenides. However, the limitations in growing atomically thin structures of tin sulfide hinder the experimental exploration of these properties. Due to the flexibility of the colloidal synthesis, it is possible to synthesize very thin and at the same time large nanosheets. Electrical transport measurements show that these nanosheets can function as field-effect transistors with an on/off ratio of more than 105 at low temperatures and p-type behavior. The temperature dependency of the charge transport reveals that defects in the crystal are responsible for the formation of holes as majority carriers. During illumination with circularly polarized light, these crystals generate a helicity dependent photocurrent at zero-volt bias, since their symmetry is broken by asymmetric interfaces (substrate and vacuum). Further, the o bserved circular photogalvanic effect shows a pronounced in-plane anisotropy, with a higher photocurrent along the armchair direction, originating from the higher absorption coefficient in this direction. Our new insights show the potential of tin sulfide for new functionalities in electronics and optoelectronics, for instance as polarization sensors.

Controlled Cracking for Large-Area Thin Film Exfoliation: Working Principles, Status, and Prospects - Yonghwan Lee, Hark Hoe Tan, C. Jagadish, Siva Krishna Karuturi (ACS Applied Electronic Materials, 2020)
The production of flexible monocrystalline semiconductor thin films less than a few tens of micrometers in thickness is currently receiving huge interest in various emerging applications such as mobile health care (mHealth), wearable devices, smart cities, and Internet of things (IoT). However, conventional techniques fail to produce wafer-scale monocrystalline thin films without the use of sophisticated equipment. Recently, the controlled cracking method has shown promise as a facile and scalable method to produce monocrystalline inorganic semiconductor thin films such as Si, Ge, III–V, and III–N materials. In this method, a crystalline semiconductor thin film can be exfoliated from its thick donor substrate via subsurface crack propagation. The cracking based layer transfer approach does not require expensive processing equipment and enables the production of multiple thin films from the same donor substrate. In this review, we present the working principles, recent progress, and fut ure prospects of this emerging crack-assisted layer transfer technology. The unique advantages of this technology for state-of-the-art flexible (opto)electronics are also highlighted. This review offers insights for the fabrication of large-scale flexible monocrystalline semiconductors, which is crucial for the development of next-generation (opto)electronics.

A high performance flexible two dimensional vertically aligned ZnO nanodisc based piezoelectric nanogenerator via surface passivation - Ketki Verma, Dhiraj Kumar Bharti, Simadri Badatya, Avanish Kumar Srivastava, Manoj Kumar Gupta (Nanoscale Advances, 2020)
were detected from the thermally annealed 2D ZnO nanodisc based nanogenerator which is approximately 8 times higher (voltage) than that from the pristine nanogenerator. It is proposed that the output performance of the vertically aligned ZnO nanodisc based nanogenerators increases due to surface passivation and reduction of oxygen vacancies.

Flexible pillar-base structured piezocomposite with aligned porosity for piezoelectric energy harvesting (Nano Energy, 2021)
Mingyang Yan a, Junwen Zhong b,*, Shengwen Liu a, Zhida Xiao a, Xi Yuan c, Di Zhai a, Kechao Zhou a, Zhaoyang Li b, Dou Zhang a,*, Chris Bowen d, Yan Zhang a,*

Porous multi-layered piezoelectric composites based on highly oriented PZT PVDF electrospinning fib (Journal of Advanced Ceramics, 2021)
Piezoelectric nanogenerators (PENGs) that can harvest mechanical energy from ambient environment have broad prospects for multi-functional applications. Here, multi-layered piezoelectric composites with a porous structure based on highly oriented Pb(Zr0.52Ti0.48)O3/PVDF (PZT/PVDF) electrospinning fibers are prepared via a laminating method to construct high-performance PENGs. PZT particles as piezoelectric reinforcing phases are embedded in PVDF fibers and facilitate the formation of polar β phase in PVDF. The multi-layered, porous structure effectively promotes the overall polarization and surface bound charge density, resulting in a highly efficient electromechanical conversion. The PENG based on 10 wt% PZT/PVDF composite fibers with a 220 µm film thickness outputs an optimal voltage of 62.0 V and a power of 136.9 μW, which are 3.4 and 6.5 times those of 10 wt% PZT/PVDF casting film-based PENG, respectively. Importantly, the PENG shows a high sensitivity of 12.4 V·N−1, presenting a s ignificant advantage in comparison to PENGs with other porous structures. In addition, the composites show excellent flexibility with a Young’s modulus of 227.2 MPa and an elongation of 262.3%. This study shows a great potential application of piezoelectric fiber composites in flexible energy harvesting devices.

Piezoelectric Nanogenerators Derived Self‐Powered Sensors for Multifunctional Applications and Artificial Intelligence - Xiaole Cao; Yao Xiong; Jia Sun; Xiaoxiao Zhu; Qijun Sun; Zhong Lin Wang (Advanced Functional Materials, 2021)
Abstract With the arrival of the Internet of Things (IoTs) era, there is a growing requirement for systems with many sensor nodes in a variety of fields of applications. The demands for wireless, sustainable and independent operation are becoming more and more important for large‐scale sensor networks and systems. For these purposes, a self‐powered sensory system that can utilize the self‐harvested energy from its surroundings to drive the sensors and directly sense external stimuli has attracted great attention. The invention and rapid development of piezoelectric generators (PENGs), which take Maxwell's displacement current as the driving force, has been pushing forward research on self‐powered active mechanical sensors, electronic skins, and human‐robotic interaction. Here, this review starts with a brief introduction of piezoelectric materials, fabrication, and performance improvement. Then, the energy harvesters used for self‐power systems based on recent progress are reviewed. Af ter that, PENGs applications toward recent self‐powered active sensors are divided into four aspects and highlighted, respectively. Moreover, some challenges and future directions for the self‐powered multifunctional sensors are put forward. It is believed that through the continuous investigations into PENG‐based self‐powered active sensors, they will soon be used in touch screens, electronic skins, health care, environmental monitoring, and intelligence systems.

3D Printing of Polyvinylidene Fluoride Based Piezoelectric Nanocomposites: An Overview (Macromolecular Materials and Engineering, 2021)
Abstract Recently, polyvinylidene fluoride (PVDF) based nanocomposites have attracted much attention for next‐generation wearable applications such as promising piezoelectric energy harvesters (nanogenerators), energy storage devices, sensing devices, and biomedical devices due to their high flexibility, and high dielectric and piezoelectric properties. 3D printing technology, PVDF based piezoelectric nanocomposites, the studies based on 3D printing of PVDF based piezoelectric nanocomposites by inkjet printing and fused deposition modeling, and enhancements of energy harvesting and storage performance of nanocomposites by structural design are comprehensively overviewed here. An insight is provided into 3D printing techniques, structure and properties of PVDF based polymers, various nanofillers and production methods for nanocomposites, solutions to enhance β phase (crystallinity) of PVDF, and improvements of nanocomposites’ breakdown strength, discharged energy density, and piezoelect ric power output by mentoring structural design.

Ionic Liquid-Assisted 3D Printing of Self-Polarized β-PVDF for Flexible Piezoelectric Energy Harvesting - Liu X, Shang Y, Zhang J, Zhang C. (ACS Applied Materials & Interfaces, 2021)
) is more than that of the reported 3D-printed PVDF piezoelectric device in the literature by two orders of magnitude. The one-step 3D printing strategy proposed in this paper can realize the rapid preparation of complex-shaped and lightweight self-polarized β-PVDF-based piezoelectric devices for energy harvesting.

Solution processed high performance piezoelectric eggshell membrane – PVDF layer composite nanogenerator via tuning the interfacial polarization (Journal of Alloys and Compounds, 2021)
Bio-compatible and eco-friendly flexible piezoelectric nanogenerators with transparency are emerging energy devices for next-generation energy application. A novel high performance natural, biodegradable and flexible eggshell membrane - polyvinylidene difluoride (PVDF) based piezoelectric nanogenerator has been developed using a low-temperature solution and spin coating route. X-ray Diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and Raman patterns exhibited all characteristic signature peaks of the eggshell membrane and PVDF film. Piezoelectric pristine PVDF, eggshell membrane and eggshell membrane-PVDF layered structure based nanogenerators are fabricated using the flexible ITO coated PET substrate and spin coating technique. The fabricated device of eggshell membrane-PVDF layer exhibited better performance with very high output voltage and current of 15 V and 150 nA as compared to 2 V and 20 nA electric output generation from pristine PVDF film based device under s ame compressive strain, without electric poling. Dielectric properties of piezoelectric PVDF film and eggshell membrane-PVDF were also measured to analyze the working mechanism of the nanogenerator. Hybrid eggshell membrane-PVDF structure shows very high dielectric constant (260) as compared to pristine PVDF (22). A very high output voltage with an average value of 65 V was also obtained from electrical poled hybrid nanogenerator under force of about 10 kgf. Such high piezoelectric output voltage and current from biodegradable eggshell membrane-PVDF based flexible piezoelectric nanogenerator was attributed to dramatic increase in interfacial polarization, capacitance and improved piezoelectric properties of PVDF and triple helical structure created polarization induced electrical dipole moment in the eggshell membrane lattice. The results not only provide a new way to utilize the solid waste for generating green energy from mechanical vibration but also an agent to increase the perform ance of the PVDF based nanogenerator for powering next generation self-powered implantable medical devices with reduced e-waste elements. (C) 2021 Elsevier B.V. All rights reserved.

Humidity Sustainable Hydrophobic Poly(vinylidene fluoride)-Carbon Nanotubes Foam Based Piezoelectric Nanogenerator - Badatya, Simadri; Bharti, Dhiraj Kumar; Sathish, Natarajan; Srivastava, Avanish Kumar; Gupta, Manoj Kumar (ACS APPLIED MATERIALS & INTERFACES, 2021)
Light weight lead free, polymer, and carbon nanotubes based flexible piezoelectric nanogenerators have prompted widespread concern for harvesting mechanical energy and powering next generation electronics devices. Herein, lightweight polyvinylidene fluoride (PVDF)-carbon nanotube (CNT) foam was prepared to fabricate humid resistant hydrophobic flexible piezoelectric nanogenerator to converts mechanical energy into electricity for the first time. Hydrophobic piezoelectric PVDF-CNT foam with density of 0.15 g/cm(3) was prepared by solution route. PVDF-CNT foam exhibited crystalline and a well-defined chain likes structure with 65% fraction of beta-phase. Self-poled PVDF-CNT foam shows piezoelectric charge coefficient (d(33)) of 9.4 pC/N. High d(33) of PVDF-CNT foam is caused by dipole alignment induced by local electric field of CNT in the microcellular structure of PVDF. The developed foam exhibits ultrahigh dielectric constant (epsilon') similar to 3048 at 150 Hz. Flexible piezoelectri c PVDF-CNT foam based nanogenerator was fabricated, which generates high output voltage similar to 12 V and current density of 30 nA/cm(2) at small compressive pressure of 0.02 kgf. Piezoelectric output performance was measured under different humid condition and an output voltage up to 8 V was achieved even under 60% RH condition. PVDF-CNT foam exhibited hydrophobic behavior and high surface water contact angle of 139 degrees. Such high output voltage even under small pressure, without applying electrical poling and under humid condition was originated though CNT induced self-alignment of electric dipoles in PVDF polymer. These excellent performances of developed foam based device confirmed its potential application in organic based ultrasensitive self-powered nanosensors and nanosystems.

Effect of dehydrofluorination reaction on structure and properties of PVDF electrospun fibers - Wang Y, Wang H, Liu K, Wang T, Yuan C, Yang H. (RSC Advances, 2021)
conductive electrodes, among which active piezoelectric materials are the most important part with excellent mechanical exibility, piezoelectricity, conductivity, sensitivity, and high energy storage.8,9 Piezoelectric materials mainly include inorganic ceramics and organic polymers. Although inorganic ceramics like barium titanate (BaTiO3) possess excellent electromechanical conversion and strong spontaneous polarization, their inherent brittleness makes them unsuitable for direct integration into exible devices.10,11 On the other hand, the piezoelectric polymer represented by poly(vinylidene uoride) (PVDF) and its copolymers, can be used as an ideal raw

Piezoelectric properties of PVDF-conjugated polymer nanofibers - Trevino, Julio E.; Mohan, Swati; Salinas, Alexandra E.; Cueva, Emilia; Lozano, Karen (JOURNAL OF APPLIED POLYMER SCIENCE, 2021)
This study presents the development and characterization of PVDF-conjugated polymer nanofiber-based systems. Five different conducting polymers (CPs) were synthesized successfully and used to create the nanofiber systems. The CPs used are polyaniline (PANI), polypyrrole (PPY), polyindole (PIN), polyanthranilic acid (PANA), and polycarbazole (PCZ). Nanofiber systems were produced utilizing the Forcespinning (R) technique. The nanofiber systems were developed by mechanical stretching. No electrical field or post-process poling was used in the nanofiber systems. The morphology, structure, electrochemical and piezoelectric performance was characterized. All of the nanofiber PVDF/CP systems displayed higher piezoelectric performance than the fine fiber PVDF systems. The PVDF/PPY nanofiber system displays the highest piezoelectric performance of 15.56 V. The piezoelectric performance of the PVDF/CP nanofiber systems favors potential for an attractive source of energy where highly flexible me mbranes could be used in power actuators, sensors and portable, and wireless devices to mention some.

Performance enhancements in poly(vinylidene fluoride)-based piezoelectric films prepared by the extrusion-casting process - ["Zhang, Chao", "Wei, Wei", "Sun, Huajun", "Zhu, Quanyao"] (JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 2021)
The extrusion-casting process can realize large-area and continuous preparation of polymer-based films. In this paper, five different types of polyvinylidene fluoride (PVDF)-based piezoelectric films: PVDF, PVDF/PZT, PVDF/PZT@105, PVDF/PZT/BNNS and PVDF/PZT@105/BNNS were prepared by the extrusion-casting process. The mechanical, dielectric, thermal conductivity and piezoelectric properties were studied. It is found that PZT particles can well improve the dielectric performance and also the mechanical stability under variable temperature conditions. PZT powders modified by titanate coupling reagent (UP-105) can further improve the performance of the PVDF/PZT@105 films by improving the combination and dispersion of organic and inorganic phases. The addition of boron nitride nanosheets (BNNS) can improve the thermal conductivity of the films and the breakdown strength. The piezoelectric coefficient (d(33)) of PVDF/PZT@105/BNNS composite film can reach 21pC/N, compared with the neat PVDF f ilm (4pC/N) and PZT/PVDF (9pC/N) film realizing great improvement.

Piezoelectric Properties of Three Types of PVDF and ZnO Nanofibrous Composites - Kim, Minji; Fan, Jintu (ADVANCED FIBER MATERIALS, 2021)
Piezoelectric materials are highly desirable for wearable electronics and energy harvesting. Piezoelectric PVDF/ZnO composite nanofibers are particularly desirable for their nontoxicity, breathability, and flexibility. Here, we investigated three methods of fabricating PVDF and ZnO composite nanofibers aimed at optimum piezoelectric responses. It was found, (1) adding ZnO nanorod as fillers within the PVDF nanofiber did not improve piezoelectric response due to the fact that the process made the material more dielectric; (2) ZnO nanorods on the PVDF surface increased the power output due to the combined effects of piezoelectricity of ZnO nanorods as well as the triboelectric response of the increased surface roughness; (3) electrospraying pre-synthesized ZnO nanorods on PVDF nanofibers resulted in the highest piezoelectric response due to the combined effect of the greater piezoelectricity of aligned ZnO nanorods and PVDF nanofibers, and larger triboelectric response from increased sur face roughness.

Rapid apatite induction of polarized hydrophilic HA/PVDF bio-piezoelectric coating on titanium surface - Wu, Cong; Tang, Yufei; Mao, Bobo; Zhao, Kang; Cao, Siyue; Wu, Zixiang (SURFACE & COATINGS TECHNOLOGY, 2021)
Coatings with piezoelectric characteristics were prepared on the titanium alloy's surface to improve its biological properties, so that the titanium alloy possessed a piezoelectric effect similar to that of bones, thereby promoting bone growth and shortening bone repair time. Compared with other piezoelectric ceramic coatings, PVDF bio-piezoelectric coatings have better piezoelectric properties. However, the PVDF coating is hydrophobic, which is not conducive to calcium deposition. In this study, HA/PVDF coating was obtained on the titanium surface, which indicated a piezoelectric effect. The hydrophilicity of the coating has been improved with the increase of HA content. Corona poling gives the HA/PVDF coating piezoelectric characteristics, and also effectively reduces the contact angle. Moreover, the contact angle of the polarized HA/PVDF coating decreased by 66.9%. The synergistic effect of the introduction of HA and the high piezoelectric coefficient promotes the coating's minerali zation. Surprisingly, the poled 20HA/PVDF coating surface was entirely covered by apatite after soaking in simulated body fluids (SBF) for 1 day with physiological loading. Additionally, the coating with rapid apatite deposition ability allows titanium alloy implants to obtain excellent biological activity, which has potential application value in the rapid repair of bone defects.

Anti-fouling piezoelectric PVDF membrane: Effect of morphology on dielectric and piezoelectric properties - Su, Yu Ping; Sim, Lee Nuang; Li, Xin; Coster, Hans G. L.; Chong, Tzyy Haur (JOURNAL OF MEMBRANE SCIENCE, 2021)
Piezoelectric membrane serves as an alternative to vibratory shear-enhanced process, which potentially offers lower cost of operation as the source of agitation is the membrane itself. The effect of morphology on dielectric and piezoelectric properties of polyvinylidene fluoride (PVDF) membranes prepared via non-solvent induced phase separation method was investigated. The membranes were fabricated using different solvents: N,N-dimethylformamide (PVDF-DMF), 1-methyl-2-pyrrolidinone (PVDF-NMP) and triethyl phosphate (PVDF-TEP). Dielectric strength analysis and piezo-response force microscopy (PFM) revealed that PVDF-DMF, displaying finger-like morphology, presented highest dielectric strength and desired piezoelectric properties. The presence of macrovoids in PVDF-NMP resulted in weak dielectric strength. Electrical poling was performed, enhancing the piezoelectric properties of membranes. No noticeable change in microstructure was observed for PVDF-NMP after poling. However, cross-sect ion morphology of PVDF-DMF visibly changed from finger-like to drop-like cavities. Infrared (IR) spectroscopy and PFM showed improvements in fraction of , beta phase and piezoelectric coefficient d(33) after poling. Cross-flow filtration experiments using colloidal silica were performed to investigate effect of electrical signal (10 Vpp, 500 Hz) on the membranes. It showed negligible effect on performance of unpoled PVDF-DMF, while 46% increase in critical flux and 66% reduction in transmembrane pressure increase (dTMP/dt) was observed for poled PVDF-DMF under electrical signal.

Incorporation of barium titanate nanoparticles in piezoelectric PVDF membrane - Su, Yu Ping; Sim, Lee Nuang; Coster, Hans G. L.; Chong, Tzyy Haur (JOURNAL OF MEMBRANE SCIENCE, 2021)
The micro-vibration of piezoelectric polyvinylidene fluoride (PVDF) membranes has been shown to mitigate fouling. To improve the desired piezoelectric properties, piezoelectric barium titanate (BaTiO3) nanoparticles (NPs) were incorporated into PVDF membranes fabricated by non-solvent induced phase separation (NIPS). Due to the high surface energy of BaTiO3 NPs, the nanoparticles tended to agglomerate and were not dispersed uniformly. The silane coupling agent (3-Aminopropyl)triethoxysilane (APTES) with the BaTiO3 NPs showed enhanced compatibility and dispersion in the PVDF membrane. The resulting BaTiO3-PVDF membranes had similar finger-like pore structure as neat PVDF membrane. The dielectric strength, piezoelectric and mechanical properties of BaTiO3-PVDF membranes were enhanced. A linear correlation (R2 = 0.9391) between piezoelectric d33 coefficient and critical flux was observed for poled BaTiO3-PVDF membranes under the influence of electrical AC signal (10 Vpp, 500 Hz) when coll oidal silica was used as model foulant. The optimal BaTiO3-PVDF membrane (0.1 wt% BaTiO3, poled and AC applied) showed up to 51% increase in critical flux compared to the neat PVDF membrane (unpoled and no AC applied). Further, extended durations of multiple filtration cycles by up to a factor of 2 to 4 were observed. The membrane operation could be prolonged due to significant reduction in irreversible fouling.

Polyvinylidene fluoride/silk fibroin-based bio-piezoelectric nanofibrous scaffolds for biomedical application - Lee, Jeong Chan; Suh, Il Won; Park, Chan Hee; Kim, Cheol Sang (JOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE, 2021)
Since the discovery that applying electrical stimulation can promote cell growth, proliferation, and tissue regeneration, research on bio-piezoelectric materials is being actively conducted. In this study, a composite material was prepared by mixing polyvinylidene fluoride (PVDF), a conventional piezoelectric polymer, and silk fibroin (SF), a natural piezoelectric material that recently attracting attention. These two polymers were fabricated into a composite fiber mat using electrospinning technology. To find optimal conditions, SF was added in various ratios to prepare electrospun PVDF/SF mats. The characteristics of these PVDF/SF composite mats were then analyzed through various evaluations and in vitro studies. It was confirmed that PVDF and SF were successfully mixed through scanning electron microscope images and structural analysis such as x-ray diffractometer and Fourier transform infrared. The results revealed that adding an appropriate amount of SF could improve the tensile s trength, enhance cell proliferation rate, and generate a voltage similar to that of a conventional PVDF-only electrospinning mat. Such fabricated electrospun PVDF/SF composite mats are expected to be useful in the bio-piezoelectric field because they can maintain piezoelectricity while compensating for the shortcomings, such as low physical properties, of a PVDF electrospun mat.

Characterization of Spongelike Porous Polyvinylidene Fluoride (PVDF) for Use as a Biosensor - Danley, Matthew (2021)

Cationic surfactant assisted enhancement of dielectric and piezoelectric properties of PVDF nanofibers for energy harvesting application - Ekbote, Govind S.; Khalifa, Mohammed; Mahendran, Arunjunairaj; Anandhan, S. (SOFT MATTER, 2021)
Poly(vinylidene fluoride) (PVDF) is among the most versatile polymers due to its wide range of properties, including dielectric, piezoelectric and ferroelectric properties. However, more frequently than not a range of processing routes and/or additives have been used to enhance such properties. In this study, PVDF nanofibers were electrospun from PVDF solution that contained tetra-n-butyl ammonium chloride (TBAC) at different loadings (1, 2, 3, and 5 wt%). The effect of TBAC on the morphology, crystallinity, and polymorphism of PVDF was studied using various characterization techniques. Addition of TBAC significantly improved the electroactive beta-phase of PVDF. The highest beta-phase content of 89% was attained at a TBAC loading of 3 wt%. Consequently, the dielectric and piezoelectric properties of the PVDF nanofibers improved significantly. A nanogenerator fabricated using 3 wt% TBAC/PVDF nanofibers exhibited the maximum voltage output of 17.2 V (under 5 N force) and the maximum pow er density of similar to 1.4 mu W cm(-2) (under 3 N force). Improved dielectric and piezoelectric properties of PVDF upon the addition of a small amount of TBAC could be useful for researchers in upbringing the material for flexible electronic devices.

Boosting piezoelectric and triboelectric effects of PVDF nanofiber through carbon-coated piezoelectric nanoparticles for highly sensitive wearable sensors - Li, Xiaoxia; Ji, Dongxiao; Yu, Bingxue; Ghosh, Rituparna; He, Jihuan; Qin, Xiaohong; Ramakrishna, Seeram (CHEMICAL ENGINEERING JOURNAL, 2021)
Piezoelectric and triboelectric effects are vital mechanisms in motion sensing. Improving both the piezoelectric performance and triboelectric effect for a single material is an important approach to further improve the sensitivity of the sensor. Herein, we achieve the enhancement of both effects in electrospun polyvinylidene fluoride (PVDF) nanofiber by simply adding carbon-coated zinc oxide (ZnO@C) nanoparticles as additive. We found that ZnO@C can not only increase the beta-phase in PVDF, resulting in an enhanced piezoelectric coefficient. It also negatively shifted the surface potential of PVDF to a high value of -740 mV, thereby modifying the triboelectric effect. The fabricated ZnO@C/PVDF nanogenerator exhibits 4 times enhancement in the voltage output, thus resulting in high sensitivity of 0.98 V kPa(-1) when used as wearable sensors. Due to the good mechanical properties of nanofibers, we also demonstrated the application of ZnO@C/PVDF nanogenerator as body motion sensor with e xcellent deformation stability. Therefore, adding carbon-coated piezoelectric nanoparticles provides an effective approach to simultaneously enhance the piezoelectric and triboelectric effects of fermelectric polymer for highly sensitive wearable sensors.

Screen-Printed Parallel-Stripes Electrodes Toward Oriented Piezoelectric Nanofibers Sensors for Both Stability and Sensitivity Improvement - Hou, Tianyuan; Zhou, Xianfeng; Xin, Yi; Lin, Tingting (IEEE SENSORS JOURNAL, 2021)
Piezoelectric nanofibers sensors cannot be mass-produced due to the limitation of electrode technology. Herein, we proposed a parallel-stripes electrode pattern for the first time, which enables using the screen-printing technology to print electrodes on piezoelectric nanofibers mats to prepare piezoelectric nanofibers sensors. Firstly, combining PVDF-TrFE nanofibers with different electrodes to prepare piezoelectric sensors and comparing their sensitivity, we prove that PVDF-TrFE nanofibers sensor based on parallel-stripes electrode has piezoelectric output. What is more, the sensor has the highest sensitivity when the parallel-stripes electrode is parallel to the oriented piezoelectric nanofibers. And then, we directly printed parallel-stripes electrode on oriented PVDF-TrFE nanofibers mat, and the vibration test of 50,000 cycles verifies that the PVDF-TrFE nanofibers sensor prepared by this way possess satisfactory stability. Our research provides a new electrode pattern for prepari ng stable and reliable electrodes for piezoelectric nanofibers sensors via screen printing. Moreover, this electrode further increases the sensitivity of the piezoelectric nanofibers sensor.

Structure-property study of pristine and dehydrofluorinated poly(vinylidene fluoride) using density functional theory - Girish, K. H.; Sainnath, P., V; Rasoor, Pavankumar B. (MONATSHEFTE FUR CHEMIE, 2021)
This study theoretically evaluates the geometrical and piezoelectric properties of pristine polyvinylidene fluoride (PVDF) and dehydrofluorinated polyvinylidene fluoride (DHF-PVDF) utilizing density functional theory. The comparative study is performed to evaluate the beta-phase enhancement capability of C=C bonds in PVDF backbone. Both the alpha and beta phases of PVDF consisting of two chains with six monomers each were theoretically analyzed at the DFT/B3LYP-D level of theory. The piezoelectric properties of the structures were interpreted by calculating dipole moments, atomic point charges, vibrational intensities, and HOMO-LUMO energies from the optimized geometries. The structural and piezoelectric properties of both pristine and dehydrofluorinated PVDF were compared with each other to evaluate the effect of double bonds on beta-phase crystallinity in modified PVDF structures. The results indicated that the inclusion of double bonds might enhance the stability and polarity of cry stalline phases in PVDF but the piezoelectric properties get diminished slightly owing to the removal of hydrogen and fluorine atoms.[GRAPHICS].

Preparation and Property Enhancement of Poly(Vinylidene Fluoride) (PVDF)/Lead Zirconate Titanate (PZT) Composite Piezoelectric Films - ["Zhang, Chao", "Sun, Huajun", "Zhu, Quanyao"] (JOURNAL OF ELECTRONIC MATERIALS, 2021)
In this paper, two methods (magnetic stirring and mechanical ball milling) were used to modify the surface of lead zirconate titanate (PZT) particles. Then, poly(vinylidene fluoride) (PVDF)/PZT piezoelectric films were prepared by extrusion casting and solvent casting. We investigated the mechanical, dielectric, ferroelectric, and piezoelectric properties, as well as the breakdown strength of the PVDF/PZT films. We found that adding PZT particles improved the mechanical stability of the films under variable temperature conditions. Modification by the UP-105 titanate coupling reagent further improved the combination and dispersion of PZT@105 particles in PVDF. The films prepared by extrusion casting showed improved properties in terms of density, dielectric constant, breakdown strength, and piezoelectric coefficient. The piezoelectric coefficient (d(33)) of the PVDF/PZT@105 composite film (with 25 wt.% PZT@105) prepared by extrusion casting reached 35 pC/N, and the electromechanical str ain ratio was almost 1.6%, which is higher than that of piezoelectric ceramics.

Property enhancement in flexible poly(vinylidene fluoride)‐based piezoelectric films with large‐area preparation (Journal of Applied Polymer Science, 2021)
Abstract Poly(vinylidene fluoride) (PVDF)‐based film exhibits high degrees of electromechanical coupling, widely applied as flexible piezoelectric sensors, soft robotics, energy harvesters, and actuators. In this article, five different types of PVDF‐based piezoelectric films were prepared by the extrusion‐casting process. The mechanical, dielectric, ferroelectric, piezoelectric, and electrically induced deformation properties of different films were studied. It is found that the addition of lead zirconate titanate (PZT) can improve the dielectric constant of piezoelectric films. PZT powders modified by titanate coupling reagent (UP‐105) can further improve the mechanical and electrical properties of composite films by improving the combination and dispersion of organic and inorganic phases. The addition of boron nitride nanosheets can effectively inhibit the generation of leak current, especially at high temperatures. The piezoelectric coefficients ( d 33 ) of composite films can reac h up to 21pC/N, and its strain ratio is about 0.6% under the electric field intensity of 200 kV/mm.

Piezoelectric Property Enhancement of PZT/Poly(vinylidenefluoride-co-trifluoroethylene) Hybrid Films for Flexible Piezoelectric Energy Harvesters (ACS Omega, 2021)
In this study, lead zirconate titanate (PZT) ceramic particles were added for further improvement. PZT belongs to the perovskite family and exhibits good piezoelectricity. Thus, it was added in this experiment to enhance the piezoelectric response of the poly(vinylideneﬂuoride-co-triﬂuoroethylene) (PVDF-TrFE) copolymer, which produced a voltage output of 1.958 V under a cyclic pressure of 290 N. In addition, to further disperse the PZT particles in the PVDF-TrFE matrix, tetradecylphosphonic acid (TDPA) was synthesized and employed to modify the PZT surface, after which the surface-modiﬁed PZT (m-PZT) particles were added to the PVDF-TrFE matrix. The TDPA on the PZT surface made it diﬃcult for the particles to aggregate, allowing them to disperse in the polymer solution more stably. In this way, the PZT particles with piezoelectric responses could be uniformly dispersed in the PVDF-TrFE ﬁlm, thereby further enhancing its overall piezoelectric response. The test results showed that upon the addition of 10 wt % m-PZT, the piezoelectric coeﬃcient of m-PZT/PVDF-TrFE 10 wt % was 27 pC/N; and under a cyclic pressure of 290 N, the output voltage reached 3.426 V, which demonstrated a better piezoelectric response than the polymer ﬁlm with the original PZT particles. Furthermore, the piezoelectric coeﬃcient of m-PZT/PVDF-TrFE 10 wt % was 27.1 pC/N. This was exhibited by maintaining a piezoelectric coeﬃcient of 26.8 pC/N after 2000 cycles. Overall, a ﬂexible piezoelectric ﬁlm with a high piezoelectric coeﬃcient was prepared by following a simple fabrication process, which showed that this ﬁlm possesses great commercial potential.

Hydrogel Ionic Diodes toward Harvesting Ultralow‐Frequency Mechanical Energy (Adv. Mater. 36/2021) - ["Yong Zhang", "Chang Kyu Jeong", "Jianjun Wang", "six others (RG visible)"] (Advanced Materials, 2021)
Energy harvesting from human motion is regarded as a promising protocol for powering portable electronics.

Hydrogel Ionic Diodes toward Harvesting Ultralow‐Frequency Mechanical Energy - ["Yong Zhang", "Chang Kyu Jeong", "Jianjun Wang", "Xin Chen", "Kyoung Hwan Choi", "Long‐Qing Chen", "Wen Chen", "Q. M. Zhang", "Qing Wang"] (Advanced Materials, 2021)
Energy harvesting from human motion is regarded as a promising protocol for powering portable electronics, biomedical devices, and smart objects of the Internet of Things.

Construction of a hierarchical multiscale conducting network for enhanced thermoelectric response in organic PEDOT:PSS based nanocomposites - ["Yong Zhang", "Siqi Liu", "J. Justin Koh", "Chaobin He"] (Journal of Materiomics, 2021)
Thermoelectric technology is an efficient and environmentally friendly route for thermal energy harvesting and solid-state cooling devices.

Ultrasensitive strain sensor based on superhydrophobic microcracked conductive Ti3C2Tx MXene/paper for human-motion monitoring and E-skin - Yibing Bu, Taoyu Shen, Wenke Yang, Shiyin Yang, Ye Zhao, Hu Liu, Yanjun Zheng, Chuntai Liu, Changyu Shen (Science Bulletin, 2021)

Self-powered, ultrasensitive, and high-resolution visualized flexible pressure sensor based on color-tunable triboelectrification-induced electroluminescence - Li Su, Zhiye Jiang, Zhen Tian, Hailu Wang, Haojie Wang, Yunlong Zi (Nano Energy, 2021)

Fabrication of hierarchically porous structured PDMS composites and their application as a flexible capacitive pressure sensor - Juwon Hwang, Yeongjun Kim, Hyeondong Yang, Je Hoon Oh (Composites Part B: Engineering, 2021)

Conductive MXene/cotton fabric based pressure sensor with both high sensitivity and wide sensing range for human motion detection and E-skin - Yanjun Zheng, Rui Yin, Ye Zhao, Hu Liu, Dianbo Zhang, Xianzhang Shi, Bing Zhang, Chuntai Liu, Changyu Shen (Chemical Engineering Journal, 2021)

Transparent, conductive cellulose hydrogel for flexible sensor and triboelectric nanogenerator at subzero temperature - Yang Hu, Meng Zhang, Chaoran Qin, Xinyi Qian, Lina Zhang, Jinping Zhou, Ang Lu (Carbohydrate Polymers, 2021)

Flexible pressure sensor with a tunable pressure-detecting range for various human motions - Gang Yang, Mao-Zhang Tian, Pei Huang, Ya-Fei Fu, Yuan-Qing Li, Ya-Qin Fu, Xiang-Qian Wang, Yao Li, Ning Hu, Shao-Yun Fu (Carbon, 2021)

GSH-responsive self-healable conductive hydrogel of highly sensitive strain-pressure sensor for cancer cell detection - Akhmad Irhas Robby, Gibaek Lee, Kang Dae Lee, Young C. Jang, Sung Young Park (Nano Today, 2021)

Constructing conductive titanium carbide nanosheet (MXene) network on polyurethane/polyacrylonitrile fibre framework for flexible strain sensor - Zhixin Jia, Zhangjie Li, Shufei Ma, Wenqiang Zhang, Yongjun Chen, Yuanfang Luo, Demin Jia, Bangchao Zhong, Joselito M. Razal, Xungai Wang, Lingxue Kong (Journal of Colloid and Interface Science, 2021)

Fabrication of capacitive pressure sensor with extraordinary sensitivity and wide sensing range using PAM/BIS/GO nanocomposite hydrogel and conductive fabric - Guanzheng Wu, Mahyar Panahi-Sarmad, Xueliang Xiao, Fuchuan Ding, Ke Dong, Xiuliang Hou (Composites Part A: Applied Science and Manufacturing, 2021)

Flexible conductive hydrogel fabricated with polyvinyl alcohol, carboxymethyl chitosan, cellulose nanofibrils, and lignin-based carbon applied as strain and pressure sensor - Mingfu Li, Qiyuan Tu, Xing Long, Qingtong Zhang, Hongrui Jiang, Changzhou Chen, Shuangfei Wang, Douyong Min (International Journal of Biological Macromolecules, 2021)

Flexible pressure sensor based on cigarette filter and highly conductive MXene sheets - Ran Li, Xiaohan Tian, Min Wei, Aijun Dong, Xi Pan, Yunlu He, Xuyan Song, Hongfei Li (Composites Communications, 2021)

Pressure-Based Biosensor Integrated with a Flexible Pressure Sensor and an Electrochromic Device for Visual Detection - Zhenzhong Yu, Guoneng Cai, Xiaolong Liu, Dianping Tang (Analytical Chemistry, 2021)

Gamma‐Ray Tolerant Flexible Pressure–Temperature Sensor for Nuclear Radiation Environment - Shuvra Mondal, Bok Ki Min, Yoonsik Yi, Van‐Tam Nguyen, Choon‐Gi Choi (Advanced Materials Technologies, 2021)
Abstract Reliable and highly sensitive flexible physical sensors hold great potential for applications in emerging technologies. Among others, of particular importance is to embed the sensor into operations at the hazardous fields, like radioactive zones or nuclear power plants. However, a significant challenge is to develop the radiation tolerant flexible sensors with stable performance under extreme conditions. This study presents a flexible pressure–temperature sensor based on MXene/Fe 3 O 4 /graphene porous network/Ecoflex (MFGPNE) and thoroughly investigates the effect of a high dose of γ‐irradiation on their physical and electrical properties. The proposed sensors are characterized by a 4.71 kPa −1 sensitivity to the applied pressure in the range of 0–62.5 kPa and by a 2.23% resistance change per degree in the temperature range of 21–110 °C. The in situ electrical experiments, performed duri ng irradiation of the MFGPNE sensor by 20 kGy of γ‐rays ( 60 Co), reveal the stable and reliable operation of the sensor. Superior radiation stability and pressure–temperature sensitivity are achieved due to the inherent nature of the materials and the sophisticated design of the proposed sensors. Moreover, an MFGPNE sensor‐based prototype gripper for grasping force control by remote monitoring of the press and lift forces demonstrates the application of the proposed sensor.

A Fully Printed Flexible Sensor Sheet for Simultaneous Proximity–Pressure–Temperature Detection (Adv. Mater. Technol. 11/2021) - Huayu Luo, Gaoyang Pang, Kaichen Xu, Zhiqiu Ye, Huayong Yang, Geng Yang (Advanced Materials Technologies, 2021)

A wearable strain sensor based on polyurethane nanofiber membrane with silver nanowires/polyaniline electrically conductive dual-network - Yu Jiang, Yixiang Chen, Wei Wang, Dan Yu (Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2021)

Thermal performance of galactitol/mannitol eutectic mixture/expanded graphite composite as phase change material for thermal energy harvesting - Tao Wang, Yang Liu, Rui Meng, Mingfu Zhang (Journal of Energy Storage, 2021)

Fabrication of PVDF/BaTiO3/NiO nanocomposite film as a separator for supercapacitors - Mandakini Sharma, Anurag Gaur (Journal of Energy Storage, 2021)

Superflexible and Lead-Free Piezoelectric Nanogenerator as a Highly Sensitive Self-Powered Sensor for Human Motion Monitoring - Di Yu, Zhipeng Zheng, Jiadong Liu, Hongyuan Xiao, Geng Huangfu, Yiping Guo (Nano-Micro Letters, 2021)
Abstract For traditional piezoelectric sensors based on poled ceramics, a low curie temperature ( T c ) is a fatal flaw due to the depolarization phenomenon. However, in this study, we find the low T c would be a benefit for flexible piezoelectric sensors because small alterations of force trigger large changes in polarization. BaTi 0.88 Sn 0.12 O 3 (BTS) with high piezoelectric coefficient and low T c close to human body temperature is taken as an example for materials of this kind. Continuous piezoelectric BTS films were deposited on the flexible glass fiber fabrics (GFF), self-powered sensors based on the ultra-thin, superflexible, and polarization-free BTS-GFF/PVDF composite piezoelectric films are used for human motion sensing. In the low force region (1–9 N), the sensors have the outstanding performance with voltage sensitivity of 1.23 V N −1 and current sensitivity of 41.0 nA N −1 . The BTS-GFF/PVDF sensors can be used to detect the tiny forces of falling water drops, finger joint motion, tiny surface deformation, and fatigue driving with high sensitivity. This work provides a new paradigm for the preparation of superflexible, highly sensitive and wearable self-powered piezoelectric sensors, and this kind of sensors will have a broad application prospect in the fields of medical rehabilitation, human motion monitoring, and intelligent robot.

A flexible and lead-free BCZT thin film nanogenerator for biocompatible energy harvesting - Shiyuan Liu, Zhuomin Zhang, Yao Shan, Ying Hong, Fatma Farooqui, Fu Shing Lam, Wei-Hsin Liao, Zuankai Wang, Zhengbao Yang (Materials Chemistry Frontiers, 2021)
High performance lead-free thin-film based piezoelectric nanogenerator.

Comparison of structural, ferroelectric, and piezoelectric properties between A-site and B-site acceptor doped 0.93Bi0.5Na0.5TiO3-0.07BaTiO3 lead-free piezoceramics - Sasipohn Prasertpalichat, Somkiet Khengkhatkan, Theeranun Siritanon, Jaru Jutimoosik, Pinit Kidkhunthod, Theerachai Bongkarn, Eric A. Patterson (Journal of the European Ceramic Society, 2021)

Low pO2 sintering and reoxidation of lead-free KNNLT piezoceramic laminates - T. Reimann, S. Fröhlich, A. Bochmann, A. Kynast, M. Töpfer, E. Hennig, J. Töpfer (Journal of the European Ceramic Society, 2021)

Low temperature calcination induced flexibility in purely inorganic lead zirconate titanate and its application in piezoelectric enhanced adsorption - Longlong Jiang, Xiao-Xiong Wang, Jun Zhang, Hao Hong, Kefan Du, Yifei Zhang, Yanqiang Li, Yongcheng Zhang, Yunze Long, Keqing Ruan (Journal of the European Ceramic Society, 2021)

Oxalic acid functionalization of BaTiO3 nanobelts for promoting their piezo-degradation organic contaminants - Shitao Gao, Hongjie Xing, Jingji Zhang, Yapi Liu, Huiwei Du, Zejie Zhu, Jiangying Wang, Xu Li, Suwei Zhang, Yaxuan Yao, Lingling Ren (Journal of Materiomics, 2021)

High efficiency degradation of tetracycline and rhodamine B using Z-type BaTiO3/γ-Bi2O3 heterojunction - Shun Zheng, Bangfu Ding, Xin Qian, Yanmin Yang, Liang Mao, Shukai Zheng, Junying Zhang (Separation and Purification Technology, 2021)

Ultrahigh degradation efficiency of AB type in-plane reverse polarization WS2 nano sheets in dark by piezo-catalyst effect - Runmin Cao, Rong Wu, Dong Zhang, Shuai Xu (Applied Surface Science, 2021)

In situpolymerization process: an essential design tool for lithium polymer batteries - Vidyanand Vijayakumar, Bihag Anothumakkool, Sreekumar Kurungot, Martin Winter, Jijeesh Ravi Nair (Energy & Environmental Science, 2021)
A comprehensive review article addressing the prospects of thein situpolymerization strategy as a tool for surpassing the challenges of electrode|electrolyte interfaces & interphases in lithium polymer batteries.

Biomass-based materials for green lithium secondary batteries - Chengbin Jin, Jianwei Nai, Ouwei Sheng, Huadong Yuan, Wenkui Zhang, Xinyong Tao, Xiong Wen Lou (Energy & Environmental Science, 2021)
This review summarizes the employment of different biomass materials for green lithium secondary batteries.

A Quasi‐Double‐Layer Solid Electrolyte with Adjustable Interphases Enabling High‐Voltage Solid‐State Batteries - Jun Pan, Yuchen Zhang, Jian Wang, Zhongchao Bai, Ruiguo Cao, Nana Wang, Shixue Dou, Fuqiang Huang (Advanced Materials, 2021)
Abstract Increasing the energy density and long‐term cycling stability of lithium‐ion batteries necessitates the stability of electrolytes under high/low voltage application and stable electrode/electrolyte interfacial contact. However, neither a single polymer nor liquid electrolyte can realize this due to their limited internal energy gap, which cannot avoid lithium‐metal deposition and electrolyte oxidation simultaneously. Herein, a novel type of quasi‐double‐layer composite polymer electrolytes (QDL‐CPEs) is proposed by using plasticizers with high oxidation stability (propylene carbonate) and high reduction stability (diethylene glycol dimethyl ether) in a poly(vinylidene fluoride) (PVDF)‐based electrolyte composites. In‐situ‐polymerized propylene carbonate can function as a cathode electrolyte interface (CEI) film, which can enhance the antioxidant ability. The nucleophilic substitution reaction between diethylene glycol dimethyl ether and PVDF increases the reduction stability o f the electrolyte on the anodic side, without the formation of lithium dendrites. The QDL‐CPEs has high ionic conductivity, an enhanced electrochemical reaction window, adjustable electrode/electrolyte interphases, and no additional electrolyte–electrolyte interfacial resistance. Thus, this ingenious design of the QDL‐CPEs improves the cycling performance of a fabricated LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811)//QDL‐CPEs//hard carbon full cell at room temperature, paving a new way for designing solid‐state battery systems accessible for practical applications.

Highly Stable Quasi‐Solid‐State Lithium Metal Batteries: Reinforced Li1.3Al0.3Ti1.7(PO4)3/Li Interface by a Protection Interlayer - Zhen Chen, Guk‐Tae Kim, Jae‐Kwang Kim, Maider Zarrabeitia, Matthias Kuenzel, Hai‐Peng Liang, Dorin Geiger, Ute Kaiser, Stefano Passerini (Advanced Energy Materials, 2021)
Abstract NASICON‐type Li 1+x Al x Ti 2−x (PO 4 ) 3 (LATP) solid electrolytes have developed as a promising candidate for solid‐state lithium batteries. However, the brittle and stiff LATP suffers from poor physical contact with electrodes and chemical/electrochemical instability at electrode|electrolyte interfaces. Herein, a thin and flexible hybrid electrolyte comprised of LATP and poly(vinylidene fluoride‐trifluorethylene) (PVDF‐TrFE) incorporated with highly concentrated ionic liquid electrolyte (ILE) is prepared to resolve these prominent limitations. To further protect the LATP|Li interface, an ultrathin poly[2,3‐bis(2,2,6,6‐tetramethylpiperidine‐N‐oxycarbonyl)‐norbornene] (PTNB) polymer is coated on Li, acting as an additional protective layer. Consequently, the lithium stripping‐plating lifetime is prolonged from 128 to 792 h, with no dendritic lithium observed. The PTNB@Li || LiNi 0.8 Co 0.1 Mn 0.1 O 2 (PTNB@Li || NCM 811 ) cells achieve significantly improved rate capability a nd cycling stability, predominantly resulting from the drastically decreased interfacial resistances, prohibited dendritic lithium generation, mitigated cathode material phase evolution, and prevention of internal microcrack formation. The thinner interphases formed on NCM 811 and PTNB@Li electrodes also play a key role. The quasi‐solid‐state batteries allow for the fabrication of multi‐layer bipolar cells with stable cycling. Even under some exertive circumstances, (limited lithium source, low temperature, e.g., 0 ° C), the impressive electrochemical performance achieved highlights the importance of such quasi‐solid‐state lithium batteries as a viable solution for the next‐generation high‐performance lithium batteries.

Polybenzimidazole functionalized electrolyte with Li‐wetting and self‐fluorination functionalities for practical Li metal batteries - Dongjiang Chen, Yuanpeng Liu, Chuan Xia, Yupei Han, Qingwei Sun, Xuchang Wang, Wei Chen, Xian Jian, Weiqiang Lv, Jianyi Ma, Weidong He (InfoMat, 2021)
Abstract Rough Li plating, low ionic conductivity, and low thermal stability of conventional electrolytes post‐primary challenges for achieving reliable high‐capacity rechargeable lithium batteries, for which lithium metal is frequently proposed as the most promising anode material. Conventional low‐polarity commercial polypropylene/polyethylene separators fail to support the application of high‐energy‐density Li anodes due to their rigid physicochemical properties and the high reactivity of Li metal, leading to fatal dendrite formation and vigorous exothermic reaction with electrolytes. Herein, we develop a Li‐wetting, flame‐retardant binary polymer electrolyte by functionalizing poly(vinylidene fluoride) (PVDF) separators with nonflammable polybenzimidazole (PBI) to build safe room‐temperature solid‐state electrolyte membranes. A dendrite‐free LiFePO 4 cell with the solid polymer electrolyte (SPE) delivers a discharge capacity of 127 mAh g −1 at 25°C with a capacity retention of 87.5 % after 500 cycles at 0.5°C (0.15 mA cm −2 ). Phase‐field simulations and density functional theory calculations demonstrate that the negatively charged benzimidazole chains of PBI own superior affinity to lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and shares overlapping electron density with Li anode, giving rise to accelerated Li + conduction at room temperature and uniform Li electrodeposition at the electrolyte/Li metal interface. The SPE is also flame‐retardant since heat‐resistant polytetrafluoroethylene and a dense, heat‐blocking graphitized carbon layer are formed in intense heat through dehydrogenation/fluorination of PVDF under the catalysis of Lewis base imidazole rings and the decomposition of benzimidazole rings in PBI. No such fire‐resistant mechanism is ever reported in conventional electrolytes. image

From Lithium‐Metal toward Anode‐Free Solid‐State Batteries: Current Developments, Issues, and Challenges - Christian Heubner, Sebastian Maletti, Henry Auer, Juliane Hüttl, Karsten D. Voigt, Oliver Lohrberg, Kristian Nikolowski, Mareike Partsch, A. Michaelis (Advanced Functional Materials, 2021)
Abstract The development of rechargeable batteries with high‐energy density is critical for future decarbonization of transportation. Anode‐free Li‐ion batteries, using a bare current collector at the anode side without any excess of Li, provide the highest volumetric energy density ( > 1500 Wh L −1 ) among all possible cell configurations. Furthermore, elimination of the anode material coating reduces material consumption and greatly simplifies cell production, which in turn lowers costs. Although significant progress has been made recently by the application of modified current collectors, optimized cycling parameters and improved liquid electrolytes, insufficient efficiencies, and dendritic growth during lithium plating lead to poor cycle life of typically less than 100 cycles as well as safety issues. Alternatively, very recent studies have demonstrated anode‐free solid‐state batteries that combine the benefits of high energy anode‐free cell configuration and solid‐state systems with high safety, exceeding 1000 cycles. This review provides an overview of recent developments toward anode‐free solid‐state batteries and highlights the current issues and challenges in this nascent field. It is concluded that, although major challenges remain at the present, the lessons learned in the fields of liquid electrolytes and solid‐state lithium metal batteries can accelerate the development of anode‐free solid‐state batteries of practical relevance.

Ultrathin Layered Double Hydroxide Nanosheets Enabling Composite Polymer Electrolyte for All‐Solid‐State Lithium Batteries at Room Temperature - Shuixin Xia, Binbin Yang, Hebin Zhang, Junhe Yang, Wei Liu, Shiyou Zheng (Advanced Functional Materials, 2021)
Abstract Solid electrolytes are the most promising substitutes for liquid electrolytes to construct high‐safety and high‐energy‐density energy storage devices. Nevertheless, the poor lithium ion mobility and ionic conductivity at room temperature (RT) have seriously hindered their practical usage. Herein, single‐layer layered‐double‐hydroxide nanosheets (SLN) reinforced poly(vinylidene fluoride‐ co ‐hexafluoropropylene) (PVDF‐HFP) composite polymer electrolyte is designed, which delivers an exceptionally high ionic conductivity of 2.2 × 10 −4 S cm −1 (25 ° C), superior Li + transfer number ( ≈ 0.78) and wide electrochemical window ( ≈ 4.9 V) with a low SLN loading ( ≈ 1 wt%). The Li symmetric cells demonstrate ultra‐long lifespan stable cycling over ≈ 900 h at 0.1 mA cm −2 , RT. Moreover, the all‐solid‐state Li|LiFePO 4 cells can run stably with a high capacity retention of 98.6% over 190 cycles at 0.1 C, RT. Moreover, using LiCoO 2 /LiNi 0.8 Co 0.1 Mn 0.1 O 2 , the all‐solid‐state lit hium metal batteries also demonstrate excellent cycling at RT. Density functional theory calculations are performed to elucidate the working mechanism of SLN in the polymer matrix. This is the first report of all‐solid‐state lithium batteries working at RT with PVDF‐HFP based solid electrolyte, providing a novel strategy and significant step toward cost‐effective and scalable solid electrolytes for practical usage at RT.

Enabling the Low-Temperature Cycling of NMC||Graphite Pouch Cells with an Ester-Based Electrolyte - Yoon-Gyo Cho, Mingqian Li, John Holoubek, Weikang Li, Yijie Yin, Ying Shirley Meng, Zheng Chen (ACS Energy Letters, 2021)
The operation of lithium-ion batteries (LIBs) at low temperatures (≤−20 °C) is limited by reduced ionic transport properties of the electrolyte, as well as by severe charge-transfer polarization. Herein, we demonstrate that this low-temperature cycling limitation can be overcome in LiNixMnyCozO2 (x + y + z = 1) (NMC)||graphite type full cells with a methyl propionate (MP)-based ester electrolyte. This electrolyte, consisting of LiPF6 dissolved in MP and fluoroethylene carbonate (FEC), delivers successful cycling at the high rate of 0.5C at −20 °C. It also sustains stable charge and discharge cycling at −40 °C with 60% capacity retention compared with room-temperature operation. This outstanding electrochemical performance is further supported by electrochemical impedance spectroscopy (EIS) in three-electrode pouch cells to investigate the internal resistances between cathode and anode, as well as careful structure and composition characterizations at the electrode interfaces. This work offers a new avenue for high-performance LIBs capable of ultralow-temperature charging–discharging operation.

Stable Interface Chemistry and Multiple Ion Transport of Composite Electrolyte Contribute to Ultra‐long Cycling Solid‐State LiNi0.8Co0.1Mn0.1O2/Lithium Metal Batteries - Ke Yang, Likun Chen, Jiabin Ma, Chen Lai, Yanfei Huang, Jinshuo Mi, Jie Biao, Danfeng Zhang, Peiran Shi, Heyi Xia, Guiming Zhong, Feiyu Kang, Yan‐Bing He (Angewandte Chemie International Edition, 2021)
Abstract Severe interfacial side reactions of polymer electrolyte with LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) cathode and Li metal anode restrict the cycling performance of solid‐state NCM811/Li batteries. Herein, we propose a chemically stable ceramic‐polymer‐anchored solvent composite electrolyte with high ionic conductivity of 6.0×10 −4 S cm −1 , which enables the solid‐state NCM811/Li batteries to cycle 1500 times. The Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 nanowires (LNs) can tightly anchor the essential N, N‐dimethylformamide (DMF) in poly(vinylidene fluoride) (PVDF), greatly enhancing its electrochemical stability and suppressing the side reactions. We identify the ceramic‐polymer‐liquid multiple ion transport mechanism of the LNs‐PVDF‐DMF composite electrolyte by tracking the 6 Li and 7 Li substitution behavior via solid‐state NMR. The stable interface chemistry and efficient ion transport of LNs‐PVDF‐DMF contribute to superior performances of the solid‐state batteries at wide temperature range of −20–60 °C.

Hunting Sodium Dendrites in NASICON-Based Solid-State Electrolytes - Qiangqiang Zhang, Yaxiang Lu, Weichang Guo, Yuanjun Shao, Lilu Liu, Jiaze Lu, Xiaohui Rong, Xiaogang Han, Hong Li, Liquan Chen, Yong‐Sheng Hu (Energy Material Advances, 2021)
NASICON- (Na superionic conductor-) based solid-state electrolytes (SSEs) are believed to be attracting candidates for solid-state sodium batteries due to their high ionic conductivity and prospectively reliable stability. However, the poor interface compatibility and the formation of Na dendrites inhibit their practical application. Herein, we directly observed the propagation of Na dendrites through NASICON-based Na 3.1 Zr 2 Si 2.1 P 0.9 O 12 SSE for the first time. Moreover, a fluorinated amorphous carbon (FAC) interfacial layer on the ceramic surface was simply developed by in situ carbonization of PVDF to improve the compatibility between Na metal and SSEs. Surprisingly, Na dendrites were effectively suppressed due to the formation of NaF in the interface when molten Na metal contacts with the FAC layer. Benefiting from the optimized interface, both the Na||Na symmetric cells and Na 3 V 2 (PO 4 ) 3 ||Na solid-state sodium batteries deliver remarkably electrochemical stability. The se results offer benign reference to the maturation of NASICON-based solid-state sodium batteries.

In situ inorganic conductive network formation in high-voltage single-crystal Ni-rich cathodes - Xinming Fan, Xing Ou, Wengao Zhao, Yun Liu, Bao Zhang, Jiafeng Zhang, Lianfeng Zou, Lukas Seidl, Yangzhong Li, Guorong Hu, Corsin Battaglia, Yong Yang (Nature Communications, 2021)
Abstract High nickel content in LiNi x Co y Mn z O 2 (NCM, x ≥ 0.8, x + y + z = 1) layered cathode material allows high specific energy density in lithium-ion batteries (LIBs). However, Ni-rich NCM cathodes suffer from performance degradation, mechanical and structural instability upon prolonged cell cycling. Although the use of single-crystal Ni-rich NCM can mitigate these drawbacks, the ion-diffusion in large single-crystal particles hamper its rate capability. Herein, we report a strategy to construct an in situ Li 1.4 Y 0.4 Ti 1.6 (PO 4 ) 3 (LYTP) ion/electron conductive network which interconnects single-crystal LiNi 0.88 Co 0.09 Mn 0.03 O 2 (SC-NCM88) particles. The LYTP network facilitates the lithium-ion transport between SC-NCM88 particles, mitigates mechanical instability and prevents detrimental crystalline phase transformation. When used in combination with a Li metal anode, the LYTP-containing SC-NCM88-based cathode enables a coin cell capacity of 130 mAh g −1 after 500 cy cles at 5 C rate in the 2.75-4.4 V range at 25 °C. Tests in Li-ion pouch cell configuration (i.e., graphite used as negative electrode active material) demonstrate capacity retention of 85% after 1000 cycles at 0.5 C in the 2.75-4.4 V range at 25 °C for the LYTP-containing SC-NCM88-based positive electrode.

Selective cobalt and nickel electrodeposition for lithium-ion battery recycling through integrated electrolyte and interface control - Kwiyong Kim, Darien Raymond, Riccardo Candeago, Xiao Su (Nature Communications, 2021)
Abstract Molecularly-selective metal separations are key to sustainable recycling of Li-ion battery electrodes. However, metals with close reduction potentials present a fundamental challenge for selective electrodeposition, especially for critical elements such as cobalt and nickel. Here, we demonstrate the synergistic combination of electrolyte control and interfacial design to achieve molecular selectivity for cobalt and nickel during potential-dependent electrodeposition. Concentrated chloride allows for the speciation control via distinct formation of anionic cobalt chloride complex (CoCl 4 2- ), while maintaining nickel in the cationic form ([Ni(H 2 O) 5 Cl] + ). Furthermore, functionalizing electrodes with a positively charged polyelectrolyte (i.e., poly(diallyldimethylammonium) chloride) changes the mobility of CoCl 4 2by electrostatic stabilization, which tunes cobalt selectivity depending on the polyelectrolyte loading. This strategy is applied for the multicomponent metal re covery from commercially-sourced lithium nickel manganese cobalt oxide electrodes. We report a final purity of 96.4 ± 3.1% and 94.1 ± 2.3% for cobalt and nickel, respectively. Based on a technoeconomic analysis, we identify the limiting costs arising from the background electrolyte, and provide a promising outlook of selective electrodeposition as an efficient separation approach for battery recycling.

Deep learning-based segmentation of lithium-ion battery microstructures enhanced by artificially generated electrodes - Simon Müller, Christina Sauter, Ramesh Shunmugasundaram, Nils Wenzler, Vincent De Andrade, Francesco De Carlo, Ender Konukoğlu, Vanessa Wood (Nature Communications, 2021)
Accurate 3D representations of lithium-ion battery electrodes, in which the active particles, binder and pore phases are distinguished and labeled, can assist in understanding and ultimately improving battery performance. Here, we demonstrate a methodology for using deep-learning tools to achieve reliable segmentations of volumetric images of electrodes on which standard segmentation approaches fail due to insufficient contrast. We implement the 3D U-Net architecture for segmentation, and, to overcome the limitations of training data obtained experimentally through imaging, we show how synthetic learning data, consisting of realistic artificial electrode structures and their tomographic reconstructions, can be generated and used to enhance network performance. We apply our method to segment x-ray tomographic microscopy images of graphite-silicon composite electrodes and show it is accurate across standard metrics. We then apply it to obtain a statistically meaningful analysis of the mi crostructural evolution of the carbon-black and binder domain during battery operation.

Photochemically driven solid electrolyte interphase for extremely fast-charging lithium-ion batteries - Minsung Baek, Jin Young Kim, Jaegyu Jin, Jang Wook Choi (Nature Communications, 2021)
Abstract Extremely fast charging (i.e. 80% of storage capacity within 15 min) is a pressing requirement for current lithium-ion battery technology and also affects the planning of charging infrastructure. Accelerating lithium ion transport through the solid-electrolyte interphase (SEI) is a major obstacle in boosting charging rate; in turn, limited kinetics at the SEI layer negatively affect the cycle life and battery safety as a result of lithium metal plating on the electrode surface. Here, we report a γ-ray-driven SEI layer that allows a battery cell to be charged to 80% capacity in 10.8 min as determined for a graphite full-cell with a capacity of 2.6 mAh cm −2 . This exceptional charging performance is attributed to the lithium fluoride-rich SEI induced by salt-dominant decomposition via γ-ray irradiation. This study highlights the potential of non-electrochemical approaches to adjust the SEI composition toward fast charging and long-term stability, two parameters that are difficu lt to improve simultaneously in typical electrochemical processes owing to the trade-off relation.

Sub-nanometer confinement enables facile condensation of gas electrolyte for low-temperature batteries - Guorui Cai, Yijie Yin, Dawei Xia, Amanda A. Chen, John Holoubek, Jonathan Scharf, Yangyuchen Yang, Ki Hwan Koh, Mingqian Li, Daniel Davies, Matthew T. Mayer, Tae Hee Han, Ying Shirley Meng, Tod A. Pascal, Zheng Chen (Nature Communications, 2021)
Abstract Confining molecules in the nanoscale environment can lead to dramatic changes of their physical and chemical properties, which opens possibilities for new applications. There is a growing interest in liquefied gas electrolytes for electrochemical devices operating at low temperatures due to their low melting point. However, their high vapor pressure still poses potential safety concerns for practical usages. Herein, we report facile capillary condensation of gas electrolyte by strong confinement in sub-nanometer pores of metal-organic framework (MOF). By designing MOF-polymer membranes (MPMs) that present dense and continuous micropore (~0.8 nm) networks, we show significant uptake of hydrofluorocarbon molecules in MOF pores at pressure lower than the bulk counterpart. This unique property enables lithium/fluorinated graphite batteries with MPM-based electrolytes to deliver a significantly higher capacity than those with commercial separator membranes (~500 mAh g −1 vs. <0. 03 mAh g −1 ) at −40 °C under reduced pressure of the electrolyte.

Innovative recycling of organic binders from electric vehicle lithium-ion batteries by supercritical carbon dioxide extraction - Yuanpeng Fu, Jonas Schuster, Martina Petraniková, Burçak Ebin (Resources Conservation and Recycling, 2021)
The growing demand for energy storage devices due to the skyrocketing production/consumption of portable electrical and electronic equipment as well as electric vehicles has promoted battery technologies, resulting in the piling of a large number of waste lithium-ion batteries (LIBs). Organic binders wrapped on electrode particles are usually the main reason that causes the difficulty of liberation and extraction of electrode materials. Pyrolysis or incineration is the general approach to separate the organic binder, leading to fluorinated exhaust gas emissions. In this study, the supercritical carbon dioxide (SC CO2) combined with a cosolvent dimethyl sulfoxide was innovatively adapted to enable the extraction of organic binders from spent LIBs to facilitate the liberation of the cathode material from aluminum foil. Pure polyvinylidene fluoride was preferentially used to study the SC CO2 dissolution mechanism. The results indicate that 98.5 wt% polyvinylidene fluoride (PVDF) dissolves in SC CO2 dimethyl sulfoxide system under the optimum conditions; 70°C process temperature, 80 bar pressure, and 13 min duration. After removing PVDF, the recovered sample was characterized by Fourier Transform Infrared Spectrometer (FTIR) and thermogravimetric analyzer (TGA) to observe its possible re-utilization. It is clear that the surficial chemical groups and content remained the same after treatment. SC CO2 processing effectively liberates the active cathode material from the aluminum substrate due to removal of the binder. The suggested innovative approach is promising as an alternative pretreatment method due to its high efficiency, relatively low energy consumption, and environmentally friendly features.

Repurposing Poly(3‐hexylthiophene) as a Conductivity‐Reducing Additive for Polyethylene‐Based High‐Voltage Insulation - Amir Masoud Pourrahimi, Sarath Kumara, Fabrizio Palmieri, Liyang Yu, Anja Lund, Thomas Hammarström, Per‐Ola Hagstrand, Ivan G. Scheblykin, Davide Fabiani, Xiangdong Xu, Christian Müller (Advanced Materials, 2021)
Poly(3-hexylthiophene) (P3HT) is found to be a highly effective conductivity-reducing additive for low-density polyethylene (LDPE), which introduces a new application area to the field of conjugated polymers. Additives that reduce the direct-current (DC) electrical conductivity of an insulation material at high electric fields have gained a lot of research interest because they may facilitate the design of more efficient high-voltage direct-current power cables. An ultralow concentration of regio-regular P3HT of 0.0005 wt% is found to reduce the DC conductivity of LDPE threefold, which translates into the highest efficiency reported for any conductivity-reducing additive to date. The here-established approach, i.e., the use of a conjugated polymer as a mere additive, may boost demand in absolute terms beyond the quantities needed for thin-film electronics, which would turn organic semiconductors from a niche product into commodity chemicals.

Opportunities from Doping of Non‐Critical Metal Oxides in Last Generation Light‐Conversion Devices - Teresa Gatti, Francesco Lamberti, Raffaello Mazzaro, Ilka Kriegel, Derck Schlettwein, Francesco Enrichi, Nicolò Lago, Eleonora Di Maria, Gaudenzio Meneghesso, Alberto Vomiero, Silvia Gross (Advanced Energy Materials, 2021)
Abstract The need to develop sustainable energy solutions is an urgent requirement for society, with the additional requirement to limit dependence on critical raw materials, within a virtuous circular economy model. In this framework, it is essential to identify new avenues for light‐conversion into clean energy and fuels exploiting largely available materials and green production methods. Metal oxide semiconductors (MOSs) emerge among other species for their remarkable environmental stability, chemical tunability, and optoelectronic properties. MOSs are often key constituents in next generation energy devices, mainly in the role of charge selective layers. Their use as light harvesters is hitherto rather limited, but progressively emerging. One of the key strategies to boost their properties involves doping, that can improve charge mobility, light absorption and tune band structures to maximize charge separation at heterojunctions. In this review, effective methods to dope MOSs and t o exploit the derived benefits in relation to performance enhancement in different types of devices are identified and critically compared. The work is focused specifically on the best opportunities coming from the use of non‐critical raw materials, so as to contribute in defining an economically feasible roadmap for light conversion technologies based on these highly stable and widely available compounds.

Engineered tunneling layer with enhanced impact ionization for detection improvement in graphene/silicon heterojunction photodetectors - Jun Yin, Lian Liu, Yashu Zang, Anni Ying, Wenjie Hui, Shusen Jiang, Chunquan Zhang, Tzu‐Yi Yang, Yu‐Lun Chueh, Jing Li, Junyong Kang (Light Science & Applications, 2021)
Abstract Here, an engineered tunneling layer enhanced photocurrent multiplication through the impact ionization effect was proposed and experimentally demonstrated on the graphene/silicon heterojunction photodetectors. With considering the suitable band structure of the insulation material and their special defect states, an atomic layer deposition (ALD) prepared wide-bandgap insulating (WBI) layer of AlN was introduced into the interface of graphene/silicon heterojunction. The promoted tunneling process from this designed structure demonstrated that can effectively help the impact ionization with photogain not only for the regular minority carriers from silicon, but also for the novel hot carries from graphene. As a result, significantly enhanced photocurrent as well as simultaneously decreased dark current about one order were accomplished in this graphene/insulation/silicon (GIS) heterojunction devices with the optimized AlN thickness of ~15 nm compared to the conventional graphene/ silicon (GS) devices. Specifically, at the reverse bias of −10 V, a 3.96-A W −1 responsivity with the photogain of ~5.8 for the peak response under 850-nm light illumination, and a 1.03-A W −1 responsivity with ∼3.5 photogain under the 365 nm ultraviolet (UV) illumination were realized, which are even remarkably higher than those in GIS devices with either Al 2 O 3 or the commonly employed SiO 2 insulation layers. This work demonstrates a universal strategy to fabricate broadband, low-cost and high-performance photo-detecting devices towards the graphene-silicon optoelectronic integration.

Strain engineering of two‐dimensional materials: Methods, properties, and applications - Shengxue Yang, Yujia Chen, Chengbao Jiang (InfoMat, 2021)
Abstract Two‐dimensional (2D) materials have attracted extensive research interests due to their excellent properties related to unique structure. Strain engineering, as an important strategy for tuning the lattice and electronic structure of 2D materials, has been widely used in the modulation of physical properties, which broadens their applications in flexible nanoelectronic and optoelectronic devices. In this review, we first summarize the methods of inducing strain to 2D materials and discuss the advantages and problems of various methods. We then introduce the strain‐induced effects on optical, electrical, and magnetic properties, together with the phase transition of 2D materials. Finally, we illustrate the potential applications of strained 2D materials and further look forward to their opportunities and challenges in practical applications in the future. image

Optical waveguides based on one-dimensional organic crystals - Song Chen, Ming‐Peng Zhuo, Xuedong Wang, Guoqing Wei, Liang‐Sheng Liao (PhotoniX, 2021)
Abstract Optical waveguide of organic micro/nanocrystals is one of crucial elements in miniaturized integrated photonics. One-dimensional (1D) organic crystals with various optical features have attracted increasing interests towards promising photonic devices, such as multichannel signal converter, organic field-effect optical waveguide, sensitive detector, and optical logic gate. Therefore, a summary about the 1D organic micro/nanocrystals based optical waveguide is important for the rational design and fabrication of novel optical devices towards optoelectronics applications. Herein, recent advances of optical waveguide based on 1D organic micro/nanocrystals with solid, flexible, hollow, uniformly doped, core-shell, multiblock and branched structures are summarized from the aspects of the waveguide properties and applications in photonic devices. Furthermore, we presented our personal view about the expectation of future development in 1D organic optical waveguide for the photonic a pplications. Graphical abstract

Challenges and Opportunities for CsPbBr3 Perovskites in Low- and High-Energy Radiation Detection - Lotte Clinckemalie, Donato Valli, Maarten B. J. Roeffaers, Johan Hofkens, Bapi Pradhan, Elke Debroye (ACS Energy Letters, 2021)
Semiconductor-based light detection finds widespread application in everyday devices. Since the fabrication of commercial photodetectors requires complex and capital-intensive equipment, a search for semiconductors with low-cost processing is essential. To this end, hybrid organic-inorganic metal halide perovskites (MHPs) have gained interest due to their facile processing, in combination with their outstanding properties, such as efficient light absorption and high carrier mobility. Recently, all-inorganic CsPbBr 3 has emerged as a promising candidate for photodetection due to its favorable intermediate bandgap and superior photostability, thermal stability, and moisture stability. Different synthesis strategies have been adopted to obtain highly crystalline CsPbBr 3 perovskites with a large variety in morphology and dimension, each allowing for a specific photodetector application, e.g., cameras for hand-held devices, large-area flat panel detectors, and flexible light sensors. This Review provides a comprehensive overview and evaluation of the state-of-the-art preparation and photodetector integration of CsPbBr 3 single crystals, microcrystals, nanowires, thin films, and nanocrystals.

Giant gauge factor of Van der Waals material based strain sensors - Wenjie Yan, Huei‐Ru Fuh, Yanhui Lv, Ke‐Qiu Chen, Tsung-Yin Tsai, Yuh‐Renn Wu, Tung-Ho Shieh, Kuan‐Ming Hung, Juncheng Li, Duan Zhang, Cormac Ó Coileáin, S. K. Arora, Zhi Wang, Zhaotan Jiang, Ching‐Ray Chang, Han‐Chun Wu (Nature Communications, 2021)
Abstract There is an emergent demand for high-flexibility, high-sensitivity and low-power strain gauges capable of sensing small deformations and vibrations in extreme conditions. Enhancing the gauge factor remains one of the greatest challenges for strain sensors. This is typically limited to below 300 and set when the sensor is fabricated. We report a strategy to tune and enhance the gauge factor of strain sensors based on Van der Waals materials by tuning the carrier mobility and concentration through an interplay of piezoelectric and photoelectric effects. For a SnS 2 sensor we report a gauge factor up to 3933, and the ability to tune it over a large range, from 23 to 3933. Results from SnS 2 , GaSe, GeSe, monolayer WSe 2 , and monolayer MoSe 2 sensors suggest that this is a universal phenomenon for Van der Waals semiconductors. We also provide proof of concept demonstrations by detecting vibrations caused by sound and capturing body movements.

Nano-patterning on multilayer MoS2 via block copolymer lithography for highly sensitive and responsive phototransistors - Heekyeong Park, Jiyoul Lee, Gyuchull Han, AbdulAziz AlMutairi, Young‐Hoon Kim, Jaichan Lee, Young‐Min Kim, Young‐Jun Kim, Youngki Yoon, Sunkook Kim (Communications Materials, 2021)
Abstract Indirect bandgap of multilayer molybdenum disulfide has been recognized as a major hindrance to high responsivity of MoS 2 phototransistors. Here, to overcome this fundamental limitation, we propose a structural engineering of MoS 2 via nano-patterning using block copolymer lithography. The fabricated nanoporous MoS 2 , consisting of periodic hexagonal arrays of hexagon nanoholes, includes abundant edges having a zigzag configuration of atomic columns with molybdenum and sulfur atoms. These exposed zigzag edges are responsible for multiple trap states in the bandgap region, as confirmed by photo-excited charge-collection spectroscopy measurements on multilayer nanoporous MoS 2 phototransistors, showing that in-gap states only near the valence band can result in a photogating effect. The effect of nano-patterning is therefore to significantly enhance the responsivity of multilayer nanoporous MoS 2 phototransistors, exhibiting an ultra-high photoresponsivity of 622.2 A W −1 . Ou r nano-patterning of MoS 2 for photosensing application paves a route to structural engineering of two-dimensional materials for highly sensitive and responsive optoelectronic devices.

Gas-mediated liquid metal printing toward large-scale 2D semiconductors and ultraviolet photodetector - Qian Li, Ju Lin, Tian-Ying Liu, Xiyu Zhu, Wenhao Yao, Jing Liu (npj 2D Materials and Applications, 2021)
Abstract A gas-mediated fabrication of centimeter-scale two-dimensional (2D) semiconductors and ultraviolet photodetector by a liquid metal-based printing was reported. Various large-scale 2D materials (Ga 2 O 3 , In 2 O 3 , SnO) were demonstrated to be directly printed at ambient air on different substrates. Such printing represents a generic, fast, clean, and scalable technique to quickly manufacture 2D semiconductors. The electrical properties were explored to quantify the printed 2D films, which were somewhat deficient in previous studies. In particular, to explore and facilitate the advantages of this 2D semiconductor in functional electronic applications, strategies for realizing fully printed Ga 2 O 3 /Si heterojunction photodetector via low-temperature and low-cost processes were developed. The device exhibits excellent sensibility and rapid photoresponse times. This work offers feasible way to develop high-performance ultraviolet photodetector for mass production. It also sugg ests a promising direction for making large-scale 2D photoelectronic and electronic systems and is expected to be extensively useful in the coming time.

Nanonet: Low-temperature-processed tellurium nanowire network for scalable p-type field-effect transistors and a highly sensitive phototransistor array - Muhammad Naqi, Kyung Hwan Choi, Hocheon Yoo, Sudong Chae, Bum Jun Kim, Seungbae Oh, Jiho Jeon, Cong Wang, Na Liu, Sunkook Kim, Jae‐Young Choi (NPG Asia Materials, 2021)
Abstract Low-temperature-processed semiconductors are an emerging need for next-generation scalable electronics, and these semiconductors need to feature large-area fabrication, solution processability, high electrical performance, and wide spectral optical absorption properties. Although various strategies of low-temperature-processed n-type semiconductors have been achieved, the development of high-performance p-type semiconductors at low temperature is still limited. Here, we report a unique low-temperature-processed method to synthesize tellurium nanowire networks (Te-nanonets) over a scalable area for the fabrication of high-performance large-area p-type field-effect transistors (FETs) with uniform and stable electrical and optical properties. Maximum mobility of 4.7 cm 2 /Vs, an on/off current ratio of 1 × 10 4 , and a maximum transconductance of 2.18 µS are achieved. To further demonstrate the applicability of the proposed semiconductor, the electrical performance of a Te-nanone t-based transistor array of 42 devices is also measured, revealing stable and uniform results. Finally, to broaden the applicability of p-type Te-nanonet-based FETs, optical measurements are demonstrated over a wide spectral range, revealing an exceptionally uniform optical performance.

Enhanced broadband nonlinear optical response of TiO 2 /CuO nanosheets via oxygen vacancy engineering - Dong Li, Hongwei Chu, Xiao Wang, Ying Li, Shengzhi Zhao, Dechun Li (Nanophotonics, 2021)
Abstract Cupric oxide (CuO), as a transition metal oxide (TMO) semiconductor, has attracted tremendous attention for various applications. In the present work, we synthesize the CuO nanosheets modified by TiO 2 nanoparticles via a facile, non‐toxic two‐step method. Subsequently, the morphology and the structures of CuO and TiO 2 /CuO nanocomposites are investigated. By utilizing the common Z‐scan technology, broadband nonlinear optical (NLO) properties of the as‐prepared CuO nanosheets and TiO 2 /CuO nanocomposites are demonstrated, elucidating the enhancement on the NLO response via the TiO 2 dopant, which is attributed to the more oxygen vacancies and the formed p‐n junctions. Furthermore, CuO nanosheets and TiO 2 /CuO nanocomposites are implemented to the passively Q‐switched bulk lasers operating in the near‐infrared (NIR) region, generating broadband ultrastable pulses. Ultimately, TiO 2 /CuO nanocomposites were intergrated in a passive mode‐locking bulk laser for the first time, achieving stable mode‐locked pulses and verifying its ultrafast optical response potential. Our results illustrate the tremendous prospects of the CuO nanosheets modified by oxygen vacancy engineering as a broadband NLO material in ultrafast photonics field.

Advances in upconversion enhanced solar cell performance - Amr Ghazy, Muhammad Safdar, Mika Lastusaari, Hele Savin, Maarit Karppinen (Solar Energy Materials and Solar Cells, 2021)
Photovoltaics (PV) is the leading renewable energy harvesting technology. Thus, there is a remarkable strive to enhance the light harvesting capability of the state-of-the-art solar cells. The major issue common to all solar cell types is that they utilize only a limited portion of the solar spectrum, mostly in the visible range, as the active semiconductor materials suffer from intrinsic light absorption thresholds. As a result, photons below and above these threshold values do not contribute to the electricity generation. A plausible solution to enhance the performance is to integrate the PV cell with an upconverting (UC) component capable of harvesting lower energy photons in the infrared (IR) range and emitting visible light. The concept was first introduced in 1990s, but major progress in the field has been made in particular in the recent few years. In this overview our intention is to provide the readers with a comprehensive account of the progress in the research on the UC-enha nced solar cells. Lanthanide ions embedded in different host lattices constitute the most important UC material family relevant to the PV technology; we first summarize the design principles and fabrication routes of these materials. Then discussed are the different approaches taken to integrate the UC layers in actual PV device configurations. Finally, we will highlight the most prominent results obtained, give some future perspectives and outline the remaining challenges in this scientifically intriguing and application-wise important field.

Solvent regulation synthesis of single-component white emission carbon quantum dots for white light-emitting diodes - Longshi Rao, Qing Zhang, Mingfu Wen, Zhongfa Mao, Huaxian Wei, Hanjui Chang, Xiaodong Niu (Nanotechnology Reviews, 2021)
Abstract White light-emitting diodes (WLEDs) hold great promise in lighting, display, and visible light communication devices, and single-component white emission carbon quantum dots (SCWE-CQDs) as the key component of WLEDs have many outstanding advantages. However, rapid and efficient synthesis of SCWE-CQDs with high photoluminescence quantum yield (PLQY) and stability remains challenging. Here, we report a novel solvent engineering strategy to obtain highly photoluminescent SCWE-CQDs by controlling the dilution ratios between N,N -dimethylformamide (DMF) and pristine red carbon quantum dots (RCQDs) solution. By optimizing synthesis conditions, the relative PLQY of the SCWE-CQDs solution reached 53%. Morphological, structural, and optical property characterizations indicate that the combined action of the hydrogen bond (HB) effect and the size effect leads to the blue shift of RCQDs, but the HB effect is more dominant than the particle size in causing large spectral shifts. In additi on, the WLEDs with high color rendering index of 89 and remarkable reliability were obtained based on the highly photoluminescent SCWE-CQDs. This facile solvent engineering approach for synthesizing tunable emission CQDs will promote the progress of carbon-based luminescent materials for applications in optoelectronic devices.

Fibre electronics: towards scaled-up manufacturing of integrated e-textile systems - Shayan Seyedin, Tian Carey, Adrees Arbab, Ladan Eskandarian, Sivasambu Böhm, Jong Min Kim, Felice Torrisi (Nanoscale, 2021)
The quest for a close human interaction with electronic devices for healthcare, safety, energy and security has driven giant leaps in portable and wearable technologies in recent years. Electronic textiles (e-textiles) are emerging as key enablers of wearable devices. Unlike conventional heavy, rigid, and hard-to-wear gadgets, e-textiles can lead to lightweight, flexible, soft, and breathable devices, which can be worn like everyday clothes. A new generation of fibre-based electronics is emerging which can be made into wearable e-textiles. A suite of start-of-the-art functional materials have been used to develop novel fibre-based devices (FBDs), which have shown excellent potential in creating wearable e-textiles. Recent research in this area has led to the development of fibre-based electronic, optoelectronic, energy harvesting, energy storage, and sensing devices, which have also been integrated into multifunctional e-textile systems. Here we review the key technological advancement s in FBDs and provide an updated critical evaluation of the status of the research in this field. Focusing on various aspects of materials development, device fabrication, fibre processing, textile integration, and scaled-up manufacturing we discuss current limitations and present an outlook on how to address the future development of this field. The critical analysis of key challenges and existing opportunities in fibre electronics aims to define a roadmap for future applications in this area.

Recent Advances in Organic and Organic Inorganic Hybrid Materials for Piezoelectric Mechanical Energ (Advanced Functional Materials, 2022)
This article provides a comprehensive overview of piezo- and ferro-electric materials based on organic molecules and organic-inorganic hybrids for mechanical energy harvesting. Molecular (organic and organic-inorganic hybrid) piezo- and ferro-electric materials exhibit significant advantages over traditional materials due to their simple solution-phase synthesis, light-weight nature, thermal stability, mechanical flexibility, high Curie temperature and attractive piezoand ferro-electric properties. However, the design and understanding of piezo- and ferro- electricity in organic and organic-inorganic hybrid materials for piezoelectric energy harvesting applications is less well developed. We describe the fundamental characterization of piezo- and ferro-electricity for a range of recently reported organic and organic-inorganic hybrid materials. First, we outline the limits of traditional piezoelectric harvesting materials, followed by an overview of the piezo- and ferro-electric propert ies of organic and organic-inorganic hybrid materials, and their composites, for mechanical energy harvesting. We provide an extensive description of peptide-based and other biomolecular piezo- and ferro-electric materials as a biofriendly alternative to current materials. Finally, we highlight current limitations and future perspectives in this emerging area of research. This perspective aims to guide chemists, materials scientists, and engineers in the design of practically useful organic and organicinorganic hybrid piezo- and ferro-electric materials and composites for mechanical energy harvesting. Contents

Corona−Poled Porous Electrospun Films of Gram−Scale Y−Doped ZnO and PVDF Composites for Piezoelectric Nanogenerators (Polymers, 2022)
For digging out eco−friendly and well−performed energy harvesters, piezoelectric nanogenerators are preferred owing to their effortless assembly. Corona−poling promotes output performance of either aligned or porous PVDF electrospun films and higher piezoelectric output was achieved by corona−poled porous PVDF electrospun films due to more poled electret dipoles in pores. Increasing the duration of electrospinning rendered more electret dipoles in PVDF porous electrospun films, resulting in higher piezoelectric output. Moreover, corona−poled PVDF/Y−ZnO porous electrospun films performed better than corona−poled PVDF/ZnO porous electrospun films because of the larger polar crystal face of Y−ZnO. Flexible piezoelectric polymer PVDF and high−piezoelectric Y−ZnO complement each other in electrospun films. With 15 wt% of Y−ZnO, corona−poled PVDF/Y−ZnO porous electrospun films generated maximum power density of 3.6 μW/cm2, which is 18 times that of PVDF/BiCl3 electrospun films.

In vitro evaluation of electrospun polyvinylidene fluoride hybrid nanoparticles as direct piezoelectric membranes for guided bone regeneration (Biomaterials Advances, 2022)
A polyvinylidene fluoride (PVDF) piezoelectric membrane containing carbon nanotubes (CNTs) and graphene oxide (GO) additives was prepared, with special emphasis on the piezoelectric activity of the aligned fibers. Fibroblast viability on membranes was measured to study cytotoxicity. Osteoprogenitor D1 cells were cultured, and mineralization of piezoelectric composite membranes was assessed by ultrasound stimulation. Results showed that the electrospun microstructures were anisotropically aligned fibers. As the GO content increased to 1.0 wt% (0.2 wt% interval), the & beta; phase in PVDF slightly increased but showed the opposite trend with the increase in CNT. Excessive addition of GO and CNT hindered the growth of the & beta; phase in PVDF. The direct piezoelectric activity and mechanical properties showed the same trend as the & beta; phase in PVDF. Moreover, GO/ PVDF with the same nanoparticle content showed better performance than CNT/PVDF composites. In this study, a comparison of the generated piezoelectric specific voltage (unit: 10-3 Vg- 1 cm- 2, linear stretch, g33) with control PVDF only (0.55 & PLUSMN; 0.16) revealed that the two composites containing 0.8 wt% GO- and 0.2 wt% CNTwith 15 wt% PVDF exhibited excellent piezoelectric voltages, which were 3.37 & PLUSMN; 1.05 and 1.45 & PLUSMN; 0.07 (10-3 Vg-1 cm-2), respectively. In vitro cultures of these two groups in contact with D1 cells showed significantly higher alkaline phosphatase secretion than the PVDF only group within 1-10 days of cell culture. Further application of ultrasound stimulation showed that the piezoelectric membrane differentiated D1 cells earlier than without ultrasound and induced higher proliferation and mineralization. This developing piezoelectric effect is expected to generate voltage through activities to enhance microcurrent stimulation in vivo.

Fluid-induced piezoelectric field enhancing photocatalytic hydrogen evolution reaction on g-C3N4/LiNbO3/PVDF membrane (Nano Energy, 2022)
Piezoelectric materials have been widely used in photocatalytic systems as it forms a built-in electric field to facilitate the migration of photo-induced charge-carriers. Herein, we report a three-dimensional (3D) porous gC3N4/LiNbO3/PVDF membrane with an enhanced fluid-induced piezoelectric field for photocatalytic hydrogen evolution reaction (HER). The freezing phase inversion strategy is critical to the formation of piezoelectric sensitive beta phase PVDF. The unique 3D porous membrane structure and the fluid-induced piezoelectric potential synergistically contribute to the HER efficiency under white light illumination. The as-prepared g-C3N4/LiNbO3/ PVDF piezoelectric photocatalytic membrane (19.6875 cm2 in size) exhibited HER rate of 136.02 mu mol h-1, which was even higher than that of the g-C3N4/LiNbO3 powder sample (111.8 mu mol h-1) with the identical mass of catalyst particles. In-situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) demonstrates a better water affinity of the porous g-C3N4/LiNbO3/PVDF piezoelectric membrane prepared by the freezing phase inversion than other PVDF membranes prepared by traditional phase inversion and vacuum drying methods. Piezoelectric force microscopy (PFM), in-situ piezoelectric and piezoelectric current measurements further visualized the fluid-induced piezoelectric field on 3D g-C3N4/LiNbO3/PVDF membrane, by which boosting the HER efficiency.