Flexible and Wearable All‐Solid‐State Supercapacitors with Ultrahigh Energy Density Based on a Carbon Fiber Fabric Electrode

Wearable textile energy storage systems are rapidly growing, but obtaining carbon fiber fabric electrodes with both high capacitances to provide a high energy density and mechanical strength to allow the material to be weaved or knitted into desired devices remains challenging. In this work, N/O‐enriched carbon cloth with a large surface area and the desired pore volume is fabricated. An electrochemical oxidation method is used to modify the surface chemistry through incorporation of electrochemical active functional groups to the carbon surface and to further increase the specific surface area and the pore volume of the carbon cloth. The resulting carbon cloth electrode presents excellent electrochemical properties, including ultrahigh areal capacitance with good rate ability and cycling stability. Furthermore, the fabricated symmetric supercapacitors with a 2 V stable voltage window deliver ultrahigh energy densities (6.8 mW h cm^?3 for fiber‐shaped samples and 9.4 mW h cm^?3 for fabric samples) and exhibit excellent flexibility. The fabric supercapacitors are further tested in a belt‐shaped device as a watchband to power an electronic watch for ≈9 h, in a heart‐shaped logo to supply power for ≈1 h and in a safety light that functions for ≈1 h, indicating various promising applications of these supercapacitors.     

Graphitic Petal Electrodes for All‐Solid‐State Flexible Supercapacitors

The charge storage characteristics of a composite nanoarchitecture with a highly functional 3D morphology are reported. The electrodes are formed by the electropolymerization of aniline monomers into a nanometer‐thick polyaniline (PANI) film that conformally coats graphitic petals (GPs) grown by microwave plasma chemical vapor deposition (MPCVD) on conductive carbon cloth (CC). The hybrid CC/GPs/PANI electrodes yield results near the theoretical maximum capacitance for PANI of 2000 F g^?1 (based on PANI mass) and a large area‐normalized specific capacitance of ≈2.6 F cm^?2 (equivalent to a volumetric capacitance of ≈230 F cm^?3) at a low current density of 1 A g^?1 (based on PANI mass). The specific capacitances remain above 1200 F g^?1 (based on PANI mass) for currents up to 100 A g^?1 with correspondingly high area‐normalized values. The hybrid electrodes also exhibit a high rate capability with an energy density of 110 Wh kg^?1 and a maximum power density of 265 kW kg^?1 at a current density of 100 A g^?1. Long‐term cyclic stability is good (≈7% loss of initial capacitance after 2000 cycles), with coulombic efficiencies >99%. Moreover, prototype all‐solid‐state flexible supercapacitors fabricated from these hybrid electrodes exhibit excellent energy storage performance.     

Integrated Conductive Hybrid Architecture of Metal–Organic Framework Nanowire Array on Polypyrrole Membrane for All‐Solid‐State Flexible Supercapacitors

Metal–organic frameworks (MOFs) with intrinsically porous structures are promising candidates for energy storage, however, their low electrical conductivity limits their electrochemical energy storage applications. Herein, the hybrid architecture of intrinsically conductive Cu‐MOF nanowire arrays on self‐supported polypyrrole (PPy) membrane is reported for integrated flexible supercapacitor (SC) electrodes without any inactive additives, binders, or substrates involved. The conductive Cu‐MOFs nanowire arrays afford high conductivity and a sufficiently active surface area for the accessibility of electrolyte, whereas the PPy membrane provides decent mechanical flexibility, efficient charge transfer skeleton, and extra capacitance. The all‐solid‐state flexible SC using integrated hybrid electrode demonstrates an exceptional areal capacitance of 252.1 mF cm^?2, an energy density of 22.4 µWh cm^?2, and a power density of 1.1 mW cm^?2, accompanied by an excellent cycle capability and mechanical flexibility over a wide range of working temperatures. This work not only presents a robust and flexible electrode for wide temperature range operating SC but also offers valuable concepts with regards to designing MOF‐based hybrid materials for energy storage and conversion systems.     

Ultrafast All‐Solid‐State Coaxial Asymmetric Fiber Supercapacitors with a High Volumetric Energy Density

Fiber‐supercapacitors (FSCs) are promising energy storage devices that can complement or even replace microbatteries in miniaturized portable and wearable electronics. Currently, a major challenge for FSCs is achieving ultrahigh volumetric energy and power densities simultaneously, especially when the charge/discharge rates exceed 1 V s^?1. Herein, an Au‐nanoparticle‐doped‐MnO_x@CoNi‐alloy@carbon‐nanotube (Au–MnO_x@CoNi@CNT) core/shell nanocomposite fiber electrode is designed, aiming to boost its charge/discharge rate by taking advantage of the superconductive CoNi alloy network and the greatly enhanced conductivity of the Au doped MnO_x active materials. An all‐solid‐state coaxial asymmetric FSC (CAFSC) prototype device made by wrapping this fiber with a holey graphene paper (HGP) exhibits excellent performance at rates up to 10 V s^?1, which is the highest charge rate demonstrated so far for FSCs based on pseudocapacitive materials. Furthermore, our fully packaged CAFSC delivers a volumetric energy density of ≈15.1 mW h cm^?3, while simultaneously maintaining a high power density of 7.28 W cm^?3 as well as a long cycle life (90% retention after 10 000 cycles). This value is the highest among all reported FSCs, even better than that of a typical 4 V/500 µA h thin‐film lithium battery.     

Free‐Standing 3D Nanoporous Duct‐Like and Hierarchical Nanoporous Graphene Films for Micron‐Level Flexible Solid‐State Asymmetric Supercapacitors

High energy density and power density within a limited volume of flexible solid‐state supercapacitors are highly desirable for practical applications. Here, free‐standing high‐quality 3D nanoporous duct‐like graphene (3D‐DG) films are fabricated with high flexibility and robustness as the backbones to deposit flower‐like MnO₂ nanosheets (3D‐DG@MnO₂). The 3D‐DG is the ideal support for the deposition of large amount of active materials because of its large surface area, appropriate pore structure, and negligible volume compared with other kinds of carbon backbones. Moreover, the 3D‐DG preserve the distinctive 2D coherent electronic properties of graphene, in which charge carriers move rapidly with a small resistance through the high‐quality and continuous chemical vapor deposition‐grown graphene building blocks, which results in a high rate performance. Marvelously, ultrathin (≈50 μm) flexible solid‐state asymmetric supercapacitors (ASCs) using 3D‐DG@MnO₂ as the positive electrode and 3D hierarchical nanoporous graphene films as the negative electrode display ultrahigh volumetric energy density (28.2 mW h cm^?3) and power density (55.7 W cm^?3) at 2.0 V. Furthermore, as‐prepared ASCs show high cycle stability clearly demonstrating their broad applications as power supplies in wearable electronic devices.     

A High‐Energy Density Asymmetric Supercapacitor Based on Fe2O3 Nanoneedle Arrays and NiCo2O4/Ni(OH)2 Hybrid Nanosheet Arrays Grown on SiC Nanowire Networks as Free‐Standing Advanced Electrodes

In this paper, a novel freestanding core‐branch negative and positive electrode material through integrating trim aligned Fe₂O₃ nanoneedle arrays (Fe₂O₃ NNAs) is first proposed with typical mesoporous structures and NiCo₂O₄/Ni(OH)₂ hybrid nanosheet arrays (NiCo₂O₄/Ni(OH)₂ HNAs) on SiC nanowire (SiC NW) skeletons with outstanding resistance to oxidation and corrosion, good conductivity, and large‐specific surface area. The original built SiC NWs@Fe₂O₃ NNAs is validated to be a highly capacitive negative electrode (721 F g^?1 at 2 A g^?1, i.e., 1 F cm^?2 at 2.8 mA cm^?2), matching well with the similarly constructed SiC NWs@NiCo₂O₄/Ni(OH)₂ HNAs positive electrode (2580 F g^?1 at 4 A g^?1, i.e., 3.12 F cm^?2 at 4.8 mA cm^?2). Contributed by the uniquely engineered electrodes, a high‐performance asymmetric supercapacitor (ASC) is developed, which can exhibit a maximum energy density of 103 W h kg^?1 at a power density of 3.5 kW kg^?1, even when charging the device within 6.5 s, the energy density can still maintain as high as 45 W h kg^?1 at 26.1 kW kg^?1, and the ASC manifests long cycling lifespan with 86.6% capacitance retention even after 5000 cycles. This pioneering work not only offers an attractive strategy for rational construction of high‐performance SiC NW‐based nanostructured electrodes materials, but also provides a fresh route for manufacturing next‐generation high‐energy storage and conversion systems.     

Digital Twin‐Driven All‐Solid‐State Battery: Unraveling the Physical and Electrochemical Behaviors

The digital twin technique has been broadly utilized to efficiently and effectively predict the performance and problems associated with real objects via a virtual replica. However, the digitalization of twin electrochemical systems has not been achieved thus far, owing to the large amount of required calculations of numerous and complex differential equations in multiple dimensions. Nevertheless, with the help of continuous progress in hardware and software technologies, the fabrication of a digital twin‐driven electrochemical system and its effective utilization have become a possibility. Herein, a digital twin‐driven all‐solid‐state battery with a solid sulfide electrolyte is built based on a voxel‐based microstructure. Its validity is verified using experimental data, such as effective electronic/ionic conductivities and electrochemical performance, for LiNi_0.70Co_0.15Mn_0.15O₂ composite electrodes employing Li₆PS₅Cl. The fundamental performance of the all‐solid‐state battery is scrutinized by analyzing simulated physical and electrochemical behaviors in terms of mass transport and interfacial electrochemical reaction kinetics. The digital twin model herein reveals valuable but experimentally inaccessible time‐ and space‐resolved information including dead particles, specific contact area, and charge distribution in the 3D domain. Thus, this new computational model is bound to rapidly improve the all‐solid‐state battery technology by saving the research resources and providing valuable insights.     

On the Functionality of Coatings for Cathode Active Materials in Thiophosphate‐Based All‐Solid‐State Batteries

The last decade has seen considerable advancements in the development of solid electrolytes for solid‐state battery applications, with particular attention being paid to sulfide superionic conductors. Importantly, the intrinsic electrochemical instability of these high‐performance separators highlights the notion that further progress in the field of solid‐state batteries is contingent on the optimization of component material interfaces in order to secure high energy and power densities, while maintaining device safety and a practical cycle life. On the cathode side, the need for a protective coating to inhibit solid electrolyte degradation is clear; however, a mechanistic understanding of the coating functionality remains unresolved, and there is still much room for improvement regarding the methodology and associated material properties. Herein, the essential requirements for a suitable coating are specified and fundamental considerations are discussed in detail. Additionally, this article will provide an overview of the various material classes, assessment protocols and practical coating methods, as well as an outlook on the development of coatings for cathode active materials in thiophosphate‐based solid‐state batteries.     

High‐Performance Fiber‐Shaped All‐Solid‐State Asymmetric Supercapacitors Based on Ultrathin MnO2 Nanosheet/Carbon Fiber Cathodes for Wearable Electronics

Flexible fiber‐shaped supercapacitors have shown great potential in portable and wearable electronics. However, small specific capacitance and low operating voltage limit the practical application of fiber‐shaped supercapacitors in high energy density devices. Herein, direct growth of ultrathin MnO₂ nanosheet arrays on conductive carbon fibers with robust adhesion is exhibited, which exhibit a high specific capacitance of 634.5 F g^?1 at a current density of 2.5 A g^?1 and possess superior cycle stability. When MnO₂ nanosheet arrays on carbon fibers and graphene on carbon fibers are used as a positive electrode and a negative electrode, respectively, in an all‐solid‐state asymmetric supercapacitor (ASC), the ASC displays a high specific capacitance of 87.1 F g^?1 and an exceptional energy density of 27.2 Wh kg^?1. In addition, its capacitance retention reaches 95.2% over 3000 cycles, representing the excellent cyclic ability. The flexibility and mechanical stability of these ASCs are highlighted by the negligible degradation of their electrochemical performance even under severely bending states. Impressively, as‐prepared fiber‐shaped ASCs could successfully power a photodetector based on CdS nanowires without applying any external bias voltage. The excellent performance of all‐solid‐state ASCs opens up new opportunity for development of wearable and self‐powered nanodevices in near future.     

Interfacial Incompatibility and Internal Stresses in All‐Solid‐State Lithium Ion Batteries

Rechargeable Li‐ion batteries (LIBs) are electrochemical storage device widely applied in electric vehicles, mobile electronic devices, etc. However, traditional LIBs containing liquid electrolytes suffer from flammability, poor electrochemical stability, and limited operational temperature range. Replacement of the liquid electrolytes with inorganic solid‐state electrolytes (SSEs) would solve this problem. However, several critical issues, such as poor interfacial compatibility, low ionic conductivity at ambient temperatures, etc., need to be surmounted before the commercialization of all‐solid‐state Li‐ion batteries (ASSLIBs). In this review, a brief historical context for the inorganic SSEs is described first. Then, two critical issues in the ASSLIBs are highlighted: interfacial incompatibility of the electrodes and SSEs and internal stresses. For the interfacial incompatibility, the discussion is focused on the dynamic characterization of the electrode/SSE interfaces, the origin and evolution of the interfacial resistance, and interface engineering to minimize the interfacial resistance. The internal stresses in the ASSLIBs are another major concern because rigid contacts are introduced. Stress generation, stress evolution during battery cycling, stress measurement/simulation, and ways to alleviate the stresses are outlined in detail. Finally, current challenges and perspectives for future development of the inorganic SSEs and ASSLIBs are outlined.     

High Performance,Flexible, Solid‐State Supercapacitors Based on a Renewable and Biodegradable Mesoporous Cellulose Membrane

A flexible, transparent, and renewable mesoporous cellulose membrane (mCel‐membrane) featuring uniform mesopores of ≈24.7 nm and high porosity of 71.78% is prepared via a facile and scalable solution‐phase inversion process. KOH‐saturated mCel‐membrane as a polymer electrolyte demonstrates a high electrolyte retention of 451.2 wt%, a high ionic conductivity of 0.325 S cm^?1, and excellent mechanical flexibility and robustness. A solid‐state electric double layer capacitor (EDLC) using activated carbon as electrodes, the KOH‐saturated mCel‐membrane as a polymer electrolyte exhibits a high capacitance of 110 F g^?1 at 1.0 A g^?1, and long cycling life of 10 000 cycles with 84.7% capacitance retention. Moreover, a highly integrated planar‐type micro‐supercapacitor (MSC) can be facilely fabricated by directly depositing the electrode materials on the mCel‐membrane‐based polymer electrolyte without using complicated devices. The resulting MSC exhibits a high areal capacitance of 153.34 mF cm^?2 and volumetric capacitance of 191.66 F cm^?3 at 10 mV s^?1, representing one of the highest values among all carbon‐based MSC devices. These findings suggest that the developed renewable, flexible, mesoporous cellulose membrane holds great promise in the practical applications of flexible, solid‐state, portable energy storage devices that are not limited to supercapacitors.     

Perovskite Membranes with Vertically Aligned Microchannels for All‐Solid‐State Lithium Batteries

Perovskite‐type solid‐state electrolytes exhibit great potential for the development of all‐solid‐state lithium batteries due to their high Li‐ion conductivity (approaching 10^?3 S cm^?1), wide potential window, and excellent thermal/chemical stability. However, the large solid–solid interfacial resistance between perovskite electrolytes and electrode materials is still a great challenge that hinders the development of high‐performance all‐solid‐state lithium batteries. In this work, a perovskite‐type Li_0.34La_0.51TiO₃ (LLTO) membrane with vertically aligned microchannels is constructed by a phase‐inversion method. The 3D vertically aligned microchannel framework membrane enables more effective Li‐ion transport between the cathode and solid‐state electrolyte than a planar LLTO membrane. A significant decrease in the perovskite/cathode interfacial resistance, from 853 to 133 Ω cm², is observed. It is also demonstrated that full cells utilizing LLTO with vertically aligned microchannels as the electrolyte exhibit a high specific capacity and improved rate performance.     

Operando Visualization of Morphological Dynamics in All‐Solid‐State Batteries

All‐solid‐state batteries (SSBs) are considered as attractive options for next‐generation energy storage owing to the favorable properties (unit transference number and thermal stabilities) of solid electrolytes. However, there are also serious concerns about mechanical deformation of solid electrolytes leading to the degradation of the battery performance. Therefore, understanding the mechanism underlying the electromechanical properties in SSBs is essentially important. Here, 3D and time‐resolved measurements of an all‐solid‐state cell using synchrotron radiation X‐ray tomographic microscopy are shown. The gradient of the electrochemical reaction and the morphological evolution in the composite layer can be clearly observed. Volume expansion/compression of the active material (Sn) is strongly oriented along the thickness of the electrode. While this results in significant deformation (cracking) in the solid electrolyte region, organized cracking patterns depending on the particle size and their arrangements is also found. This study based on operando visualization therefore opens the door toward rational design of particles and electrode morphology for all‐solid‐state batteries.     

All‐Solid‐State Printed Bipolar Li–S Batteries

Despite their potential advantages over currently widespread lithium‐ion batteries, lithium–sulfur (Li–S) batteries are not yet in practical use. Here, for the first time bipolar all‐solid‐state Li–S batteries (ASSLSBs) are demonstrated that exhibit exceptional safety, flexibility, and aesthetics. The bipolar ASSLSBs are fabricated through a solvent‐drying‐free, ultraviolet curing‐assisted stepwise printing process at ambient conditions, without (high‐temperature/high‐pressure) sintering steps that are required for inorganic electrolyte‐based all‐solid‐state batteries. Two thermodynamically immiscible and nonflammable gel electrolytes based on ethyl methyl sulfone (EMS) and tetraethylene glycol dimethyl ether (TEGDME) are used to address longstanding concerns regarding the grain boundary resistance of conventional inorganic solid electrolytes, as well as the polysulfide shuttle effect in Li–S batteries. The EMS gel electrolytes embedded in the sulfur cathodes facilitate sulfur utilization, while the TEGDME gel composite electrolytes serve as polysulfide‐repelling separator membranes. Benefiting from the well‐designed cell components and printing‐driven facile processability, the resulting bipolar ASSLSBs exhibit unforeseen advancements in bipolar cell configuration, safety, foldability, and form factors, which lie far beyond those achievable with conventional Li–S battery technologies.