Layered double hydroxides as electrode materials for flexible energy storage devices

To prevent and mitigate environmental degradation,high-performance and cost-effective electrochemical flexible energy storage systems need to be urgently developed.This demand has led to an increase in research on electrode materials for high-capacity flexible supercapacitors and secondary batteries,which have greatly aided the development of contemporary digital communications and electric vehicles.The use of layered double hydroxides(LDHs)as electrode materials has shown productive results over the last decade,owing to their easy production,versatile composition,low cost,and excellent physicochemical features.This review highlights the distinctive 2D sheet-like structures and electrochemical characteristics of LDH materials,as well as current developments in their fabrication strategies for expanding the application scope of LDHs as electrode materials for flexible supercapacitors and alkali metal(Li,Na,K)ion batteries.

Graphene-based materials for flexible energy storage devices

The booming developments in portable and wearable electronics promote the design of flexible energy storage systems. Flexible supercapacitors and batteries as promising energy storage devices have attracted tremendous attention. As the key component of both supercapacitors and batteries, electrode materials with excellent flexibility should be considered to match with highly flexible energy storage devices. Owing to large surface area, good thermal and chemical stability, high conductivity and mechanical flexibility,graphene-based materials have been widely employed to serve as promising electrodes of flexible energy storage devices. Considerable efforts have been devoted to the fabrication of flexible graphene-based electrodes through a variety of strategies. Moreover, different configurations of energy storage devices based on these active materials are designed. This review highlights flexible graphene-based two-dimensional film and one-dimensional fiber supercapacitors and various batteries including lithium-ion, lithium–sulfur and other batteries. The challenges and promising perspectives of the graphene-based materials for flexible energy storage devices are also discussed.

Highly elastic energy storage device based on intrinsically super-stretchable polymer lithium-ion conductor with high conductivity

Stretchable power sources,especially stretchable lithium-ion batteries(LIBs),have attracted increasing attention due to their enormous prospects for powering flexible/wearable electronics.Despite recent advances,it is still challenging to develop ultra-stretchable LIBs that can withstand large deformation.In particular,stretchable LIBs require an elastic electrolyte as a basic component,while the conductivity of most elastic electrolytes drops sharply during deformation,especially during large deformations.This is why highly stretchable LIBs have not yet been realized until now.As a proof of concept,a super-stretchable LIB with strain up to 1200%is created based on an intrinsically super-stretchable polymer electrolyte as the lithium-ion conductor.The super-stretchable conductive system is constructed by an effective diblock copolymerization strategy via photocuring of vinyl functionalized 2-ureido-4-pyrimidone(VFUpy),an acrylic monomer containing succinonitrile and a lithium salt,achieving high ionic conductivity(3.5×10^(-4)mS cm^(-1)at room temperature(RT))and large deformation(the strain can reach 4560%).The acrylic elastomer containing Li-ion conductive domains can strongly increase the compatibility between the neighboring elastic networks,resulting in high ionic conductivity under ultra-large deformation,while VFUpy increases elasticity modulus(over three times)and electrochemical stability(voltage window reaches 5.3 V)of the prepared polymer conductor.At a strain of up to 1200%,the resulting stretchable LIBs are still sufficient to power LEDs.This study sheds light on the design and development of high-performance intrinsically super-stretchable materials for the advancement of highly elastic energy storage devices for powering flexible/wearable electronics that can endure large deformation.

Engineering Geometric Electrodes for Electric Field-Enhanced High-Performance Flexible In-Plane Micro-Supercapacitors

In plane micro-supercapacitors that are miniaturized energy storage components have attracted significant attention due to their high power densities for various ubiquitous and sustainable device systems as well as their facile integration on various flexible/wearable platform.To implement the micro-supercapacitors in various practical applications that can accompany solid state or gel electrolyte and flexible substrates,ions must be readily transported to electrodes for achieving high power densities.Herein,we show large enhancement in electrochemical properties of flexible,inplane micro-supercapacitor using sharp-edged interdigitated electrode design,which was simply fabricated through direct laser scribing method.The sharp-edged electrodes allowed strong electric field to be induced at the corners of the electrode fingers which led to the greater accumulation of ions near the surface of electrode,significantly enhancing the energy storage performance of micro-supercapacitors.The electric field-enhanced in-plane micro-supercapacitor showed the volumetric energy density of 1.52 Wh L^(−1)and the excellent cyclability with capacitive retention of 95.4%after 20000 cycles.We further showed various practicability of our sharp-edged design in micro-supercapacitors by showing circuit applicability,mechanical stability,and air stability.These results present an important pathway for designing electrodes in various energy storage devices.

Flexible sodium-ion capacitors boosted by high electrochemicallyreactive and structurally-stable Sb_(2)S_(3)nanowire/Ti_(3)C_(2)Tx MXene film anodes

The rapid development of portable,foldable,and wearable electronic devices requires flexible energy storage systems.Sodiumion capacitors(SICs)combining the high energy of batteries and the high power of supercapacitors are promising solutions.However,the lack of flexible and durable electrode materials that allow fast and reversible Na+storage hinders the development of flexible SICs.Herein,we report a high-capacity,free-standing and flexible Sb2S3/Ti_(3)C_(2)Tx composite film for fast and stable sodium storage.In this hybrid nano-architecture,the Sb_(2)S_(3)nanowires uniformly anchored between Ti_(3)C_(2)Tx nanosheets not only act as sodium storage reservoirs but also pillar the two-dimensional(2D)Ti_(3)C_(2)Tx to form three-dimensional(3D)channels benefiting for electrolyte penetration.Meanwhile,the highly conductive Ti_(3)C_(2)Tx nanosheets provide rapid electron transport pathways,confine the volume expansion of Sb_(2)S_(3)during sodiation,and restrain the dissolution of discharged sodium polysulfides through physical constraint and chemical absorption.Owing to the synergistic effects of the one-dimensional(1D)Sb_(2)S_(3)nanowires and 2D MXenes,the resultant composite anodes exhibit outstanding rate performance(553 mAh·g−1 at 2 A·g−1)and cycle stability in sodium-ion batteries.Moreover,the flexible SICs using Sb2S3/Ti_(3)C_(2)Tx anodes and active carbon/reduced graphene oxide(AC/rGO)paper cathodes deliver a superior energy and power density in comparison with previously reported devices,as well as an excellent cycling performance with a high capacity retention of 82.78%after 5,000 cycles.This work sheds light on the design of next-generation low-cost,flexible and fast-charging energy storage devices.