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Although recognized as an important component of all energy storage and conversion technologies, electrochemical supercapacitators (ES) still face development challenges in order to reach their full potential. A thorough examination of development in the technology during the past decade, Electrochemical Supercapacitors for Energy Storage and Delivery: Fundamentals and Applications provides a comprehensive introduction to the ES from technical and practical aspects and crystallization of the technology, detailing the basics of ES as well as its components and characterization techniques. The book illuminates the practical aspects of understanding and applying the technology within the industry and provides sufficient technical detail of newer materials being developed by experts in the field which may surface in the future. The book discusses the technical challenges and the practical limitations and their associated parameters in ES technology. It also covers the structure and options for device packaging and materials choices such as electrode materials, electrolyte, current collector, and sealants based on comparison of available data. Supplying an in depth understanding of the components, design, and characterization of electrochemical supercapacitors, the book has wide-ranging appeal to industry experts and those new to the field. It can be used as a reference to apply to current work and a resource to foster ideas for new devices that will further the technology as it becomes a larger part of main stream energy storage.

Given the rise in the popularity of wearable electronics that are able to deform into desirable configurations while maintaining electrochemical functionality, stretchable and flexible (hybrid) supercapacitors (SCs) have become increasingly of interest as innovative energy storage devices. Their outstanding power density, long lifetime with low capacitance loss, and appropriate energy density, in particular in hybrid cases make them ideal candidates for flexible electronics. The aim of this review paper is to provide an in‐depth discussion of these stretchable and flexible SCs ranging from fabrication to electro‐mechanical properties. This review paper begins with a short overview of the fundamentals of charge storage mechanisms and different types of multivalent metal‐ion hybrid SCs. The research methods leading up to the current state of these stretchable and flexible SCs are then presented. This is followed by an in‐depth presentation of the challenges associated with the fabrication methods for different configurations. Proposed novel strategies to maximize the elastic and electrochemical properties of stretchable/flexible or quasi‐solid‐state SCs are classified and the pros and cons associated with each are shown. The advances in mechanical properties and the expected advancements for the future of these SCs are discussed in the last section. The recent advancements and future potential application potential of flexible and stretchable supercapacitors (SCs) and hybrid SCs with different configurations have been studied. Mechanisms associated with energy storage, layouts, energy materials, different configurations, and their effects on mechanical and electrochemical properties are studied. Manufacturing methods associated with different device configurations and challenges are discussed.

One of the most exciting new developments in energy storage technology is flexible Zn‐ion hybrid supercapacitors (f‐ZIHSCs), which combine the high energy of Zn‐ion batteries with high‐power supercapacitors to satisfy the needs of portable flexible electronics. However, the development of f‐ZHSCs is still in its infancy, and there are numerous barriers to overcome before they can be widely implemented for practical applications. This review gives an up‐to‐date description of recent achievements and underlying concepts in energy storage mechanisms of f‐ZIHSCs and emphasizes the critical role of cathode, anode, and electrolyte materials systems in speeding the prosperity of f‐ZIHSCs. The innovative nanostructured‐based cathode materials for f‐ZIHSCs include carbon (e.g., porous carbon, heteroatom‐doped carbon, biomass‐derived porous carbon, graphene, etc.), metal‐oxides, MXenes, and metal/covalent‐organic frameworks, and other materials (e.g., activated carbon, phosphorene, etc.) are mainly focused. Afterward, the latest developments in flexible anode and electrolyte frameworks and impacts of electrolyte compositions on the electrochemical properties of f‐ZIHSC are elaborated. Subsequently, the advancements based on fabrication designs, including quasi‐solid‐state, micro, fiber‐shaped, and all climate‐changed f‐ZIHSCs, are discussed in detail. Lastly, a summary of current challenges and recommendations for the future progress of advanced f‐ZIHSC are addressed. This review article is anticipated to further understand the viable strategies and achievable approaches for assembling high‐performance f‐ZIHSCs and boost the technical revolutions on cathode, anode, and electrolytes for f‐ZIHSC devices. This review gives an up‐to‐date description of recent achievements and underlying concepts in energy storage mechanisms of flexible Zn‐ion hybrid supercapacitors (f‐ZIHSCs) and emphasizes the critical role of cathode, anode, and electrolyte materials systems in speeding the prosperity of f‐ZIHSCs. Subsequently, the advancements based on fabrication designs, including quasi‐solid‐state, micro, fiber‐shaped, and all climate‐changed f‐ZIHSCs, are discussed in detail.

The rapid development of wearable, highly integrated, and flexible electronics has stimulated great demand for on-chip and miniaturized energy storage devices. By virtue of their high power density and long cycle life, micro-supercapacitors (MSCs), especially those with interdigital structures, have attracted considerable attention. In recent years, tremendous theoretical and experimental explorations have been carried out on the structures and electrode materials of MSCs, aiming to obtain better mechanical and electrochemical properties. The high-performance MSCs can be used in many fields, such as energy storage and medical assistant examination. Here, this review focuses on the recent progress of advanced MSCs in fabrication strategies, structural design, electrode materials design and function, and integrated applications, where typical examples are highlighted and analyzed. Furthermore, the current challenges and future development directions of advanced MSCs are also discussed.

Stretchable and flexible supercapacitors are highly desired due to their many potential applications in wearable devices. However, it is challenging to fabricate supercapacitors that can withstand large tensile strain while maintaining high performance. Herein, we report an ultra-stretchable wire-shaped supercapacitor based on carbon nanotube@graphene@MnO 2 fibers wound around a superelastic core fiber. The supercapacitor can sustain tensile strain up to 850%, which is the highest value reported for this type of device to date, while maintaining stable electrochemical performance. The energy density of the supercapacitor is 3.37 mWh·cm –3 at a power density of 54.0 mW·cm –3 . The results show that 82% of the specific capacitance is retained after 1,000 stretch–release cycles with strains of 700%, demonstrating the superior durability of the elastic supercapacitor and showcasing its potential application in ultra-stretchable flexible electronics.

Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxygen and hydrogen content. This sp 2 -bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.

An exciting new area of research is the development of metal–organic framework (MOF)-based materials that exhibit desirable conductivity, vigorous redox activity, and a large specific surface area that can be used as electrodes in supercapacitors. However, upon direct application to electrode materials in supercapacitors, the MOFs exhibit insufficient electrical conductivity and unsatisfactory stability, thereby impeding the advancement of their electrochemical characteristics. In this study, we extensively examine the hydrothermally synthesized nickel/copper metal–organic framework (MOF) and its composite material, comprising nickel/copper MOF and polyaniline. The composite material was prepared using a physical blending process for the purpose of developing a high energy density supercapattery device. The specific capacity of the hydrothermally synthesized nickel/copper–MOF/PANI is observed to be 651 C g −1 under an initial current density of 1 A g −1 in a three-electrode electrochemical system. Due to its exceptional electrochemical properties, the as-synthesized composite is employed to construct battery-type electrodes for practical device production. This is achieved by combining it with a highly porous (activated carbon) electrode, which is separated by a cellulose paper. The assembled NiCu–MOF/PANI//AC device exhibited a specific capacity of 220 C g −1 , along with an energy density of 60 W h kg −1 , when subjected to a current density of 1 A g −1 . The constructed device exhibited improved cyclic stability, maintaining a remarkable capacitance retention rate of approximately 94.8% even after undergoing 15,000 cycles. The potential applications of this composite electrode encompass high-performance supercapacitors, flexible electronics, and wearable technological devices.

The recently emerging laser-induced graphene (LIG) technology, with one-step processing and designable features, has been widely used in the fabrication of wearable/portable electronics. Herein, by taking inspiration from kirigami, we designed a stretchable supercapacitor (SC) step by step through controlling laser induction and cutting process on the polyimide (PI) film, with the use of one single CO2 laser source. Firstly, the carbonized basic geometric units of lines were produced on PI films to investigate the processing-structure relationships. Then, the complex photothermal conversion and heat transfer progress involved in the carbonized process were simulated by a photothermal model. Both experimental and theoretical results suggested that the laser power, scan rate and focus condition have great influence on the size, shape and morphology of the carbonized lines. Finally, we optimized the parameters of laser induction and cutting process to fabricate the kirigami-inspired SCs with reliable electrochemical properties and editable mechanical flexibility, showing great potential in the field of flexible electronics.

Freestanding films with high strength and conductivity are critical for flexible electronics, such as supercapacitors. Herein, inspired from the natural leaf, a freestanding paper is constructed through fast vacuum filtration by “mesophylls‐like” MXene (Ti3C2TX) nanosheets and “vein‐like” cellulose filaments and silver nanowires (Ag NWs). The produced nanocomposite paper with 25 wt% Ti3C2TX and 8 wt% Ag NWs (PMxAg25‐8) exhibits high conductivity (58 843 S m−1) and excellent mechanical properties (Tensile strength of 34 MPa and Young's modulus of 6 GPa), which arises from the synergistic effects of the interactions between cellulose and MXene and the three‐dimensional interpenetrating frameworks. This interpenetrating framework can further benefit the electrochemical performance of the nanocomposite papers and the foldable paper electrode presents a high capacitance of 505 F g−1 with only 25 wt% MXene. This work paves the way for the fast fabrication of strong and multifunctional MXene macro‐assembly for flexible electronics by conventional papermaking process. The freestanding paper composed of “mesophylls‐like” MXene nanosheets and “vein‐like” cellulose filaments and silver nanowires has been constructed by the traditional papermaking process. The resulted paper electrode exhibits good mechanical properties, high conductivity and excellent electrochemical performance with fast ion/charge transport channel, showing big potential in flexible electronics.

HighlightsAn all-covalent organic framework (COF) nanofilm-structured lithium-ion capacitor (LIC) was developed by custom-made COF nanofilms as the anode/cathode.The COF nanofilm-structured LIC exhibits good electrochemical properties via the fast Li+ transport kinetics of the anodic COFBTMB-TP nanofilm and the high specific capacity of the cathodic COFTAPB-BPY nanofilm.This work can realize the charge storage kinetics and capacity balance of anode/cathode in COFTAPB-BPY//COFBTMB-TP LIC.Free-standing covalent organic framework (COFs) nanofilms exhibit a remarkable ability to rapidly intercalate/de-intercalate Li+ in lithium-ion batteries, while simultaneously exposing affluent active sites in supercapacitors. The development of these nanofilms offers a promising solution to address the persistent challenge of imbalanced charge storage kinetics between battery-type anode and capacitor-type cathode in lithium-ion capacitors (LICs). Herein, for the first time, custom-made COFBTMB-TP and COFTAPB-BPY nanofilms are synthesized as the anode and cathode, respectively, for an all-COF nanofilm-structured LIC. The COFBTMB-TP nanofilm with strong electronegative–CF3 groups enables tuning the partial electron cloud density for Li+ migration to ensure the rapid anode kinetic process. The thickness-regulated cathodic COFTAPB-BPY nanofilm can fit the anodic COF nanofilm in the capacity. Due to the aligned 1D channel, 2D aromatic skeleton and accessible active sites of COF nanofilms, the whole COFTAPB-BPY//COFBTMB-TP LIC demonstrates a high energy density of 318 mWh cm−3 at a high-power density of 6 W cm−3, excellent rate capability, good cycle stability with the capacity retention rate of 77% after 5000-cycle. The COFTAPB-BPY//COFBTMB-TP LIC represents a new benchmark for currently reported film-type LICs and even film-type supercapacitors. After being comprehensively explored via ex situ XPS, 7Li solid-state NMR analyses, and DFT calculation, it is found that the COFBTMB-TP nanofilm facilitates the reversible conversion of semi-ionic to ionic C–F bonds during lithium storage. COFBTMB-TP exhibits a strong interaction with Li+ due to the C–F, C=O, and C–N bonds, facilitating Li+ desolation and absorption from the electrolyte. This work addresses the challenge of imbalanced charge storage kinetics and capacity between the anode and cathode and also pave the way for future miniaturized and wearable LIC devices.