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Lithium‐ion batteries have attracted much attention in the field like portable devices and electronic vehicles. Due to growing demands of energy storage systems, lithium metal batteries with higher energy density are promising candidates to replace lithium‐ion batteries. However, using excess amounts of lithium can lower the energy density and cause safety risks. To solve these problems, it is crucial to use limited amount of lithium in lithium metal batteries to achieve higher utilization efficiency of lithium, higher energy density, and higher safety. The main reasons for the loss of active lithium are the side reactions between electrolyte and electrode, growth of lithium dendrites, and the volume change of electrode materials during the charge and discharge process. Based on these issues, much effort have been put to improve the utilization efficiency of lithium such as mitigating the side reactions, guiding the uniform lithium deposition, and increasing the adhesion between electrolyte and electrode. In this review, strategies for high utilization efficiency of lithium are presented. Moreover, the remaining challenges and the future perspectives on improving the utilization of lithium are also outlined. [ABSTRACT FROM AUTHOR]

Biphasic self-stratified batteries (BSBs) provide a new direction in battery philosophy for large-scale energy storage, which successfully reduces the cost and simplifies the architecture of redox flow batteries. However, current aqueous BSBs have intrinsic limits on the selection range of electrode materials and energy density due to the narrow electrochemical window of water. Thus, herein, we develop nonaqueous BSBs based on Li-S chemistry, which deliver an almost quadruple increase in energy density of 88.5 Wh L−1 as compared with the existing aqueous BSBs systems. In situ spectral characterization and molecular dynamics simulations jointly elucidate that while ensuring the mass transfer of Li+, the positive redox species are strictly confined to the bottom-phase electrolyte. This proof-of-concept of Li-S BSBs pushes the energy densities of BSBs and provides an idea to realize massive-scale energy storage with large capacitance. The use of energy-dense materials is inherently limited in biphasic self-stratified batteries due to the aqueous electrolyte environment. Here, the authors extended the concept of biphasic self-stratified batteries to non-aqueous systems, resulting in increased energy density and output voltage. [ABSTRACT FROM AUTHOR]

As a vital technology in portable electronic equipment, electric vehicle, and stationary energy storage, lithium‐based batteries are currently gaining widespread attention. However, when batteries are used more frequently, there are greater worries regarding their susceptibility to temperature, especially at low temperatures (LTs). In this review, the factors that lead to capacity loss in lithium‐based batteries at LT are analyzed and a summary of the most recent cutting‐edge approaches for improving LT kinetics is provided. In order to achieve satisfactory LT performance, electrode technology, interface chemistry, and electrolyte engineering must be taken into account during the cell design process. The recently revealed unique cryogenic storage mode and design concepts are also thoroughly introduced in this review, which is intended to motivate researchers in related domains. Finally, new insights, intriguing concepts, and workable solutions are proposed to promote the ongoing development of high‐performance cryogenic lithium batteries. [ABSTRACT FROM AUTHOR]

Zn is a promising anode for aqueous energy storage owing to it intrinsic superior properties such as large capacity, abundant reserves, low potential and safety. But, the growth of dendrites during charge and discharge leads to a decrease in reversibility. In addition, further development of zinc‐ion hybrid capacitors (ZICs) is seriously challenging because of the lack of an exceptional cathode. Herein, we use ZIF‐8 annealed at 500 °C (annealed ZIF‐8) as a host material for stable and dendrite‐free Zn anodes. Utilization of annealed ZIF‐8 results in dendrite‐free Zn deposition and stripping as a result of its porous construction, which contains trace Zn. Furthermore, we firstly proposed innovative N,O dual‐doped carbon which was designed by the derived ZIF‐8 (ZIF‐8 derived C) as cathode for high‐energy and power‐density ZICs. The new ZIC assembled by Zn@annealed ZIF‐8 anode and ZIF‐8 derived C cathode provides a capacity of 135.5 mAh g−1 and an energy density of 108.4 Wh kg−1 with a power density of 800 W kg−1 at 1.0 A g−1. In addition, it shows outstanding cycling stability of 91% capacity retention after 6000 cycles at 5.0 A g−1. Moreover, the solid‐state ZICs can drive LEDs and smart watches. This ZIC holds promise for the practical application of supercapacitors. [ABSTRACT FROM AUTHOR]

• MOFs were utilized as templates to obtain porous nanostructure. • Electrochemical activation endowed CC with excellent hydrophilic property. • Unique hydrolysis and ion exchange/etching method was used in this work. • The hybrid supercapacitor exhibited excellent flexibility and wearability. Flexible electrodes with favorable architectures are urgently demanded for flexible and wearable supercapacitors with high performance. Herein, we demonstrate the rational design and preparation of hollow and ultrathin nickel cobalt sulfides nanosheets arrays on electrochemical activated carbon cloth (Ni-Co-S/ACC) for fabrication of flexible hybrid supercapacitors, where the Ni-Co-S nanosheets are derived from the metal-organic framework via an etching/ion exchange method. The Ni-Co-S/ACC electrode can deliver a very high specific capacitance of 2392 F/g at the current density of 1 A/g and good rate performance (80.3% capacitance retention at 20 A/g). The enhanced electrochemical properties should be attributed to the hydrophilic property, good conductivity and enriched redox active sites resulted from the electrochemical activated carbon cloth and the hollow and ultrathin structure of Ni-Co-S nanosheets. When a flexible hybrid supercapacitor is assembled using Ni-Co-S/ACC as positive electrode and activated carbon as negative electrode, it shows high energy density of 30.1 Wh/Kg at power density of 800.2 W/Kg as well as predominant cycling stability (82% retention after 10,000 cycles). Furthermore, the excellent flexibility and wearability of the hybrid supercapacitor could envision promising applications in high-performance wearable energy storage devices. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Thermally-treated and acid-etched method is utilized to obtain flexible carbon fiber cloth. • N/O-enriched carbon fibers exhibit high surface area and large pore volume. • N- and O-rich functional groups can generate high pseudocapacitance. • The electrode based on N/O-enriched carbon fibers cloth shows prominent area-capacitance and flexibility. Abstract The fast development of portable devices has greatly stimulated the demand for flexible supercapacitors (FSCs). The key to assembling FSCs lies in the development of electrodes with high-performance and good flexibility. In this work, oxygeneous groups modified nitrogen-doped carbon fibers cloth (ONCC) was obtained through annealing the pre-oxidized polyacrylonitrile cloth (PPC), followed by a facile oxidation process using a mixture of concentrated sulfuric acid and concentrated nitric acid. By changing annealing temperature, the nitrogen content can be controlled in the obtained ONCC. It was found that the PPC annealed at 950 °C followed by acid etching for 60 min could deliver the excellent areal and gravimetric specific capacitance of 1385 mF cm−2 and 294.7 F g−1 at the current density of 1 mA cm−2, outstanding rate performance and superb cycling stability. Furthermore, the assembled FSC delivered a high energy density of 19.8 μWh cm−2 (4.03 Wh kg−1) at a power density of 50.1 μW cm−2 (10.2 W kg−1) and good flexibility under different bending conditions. This work provides a facile and efficient route to prepare high-performance carbon fiber based electrode materials in large scale for flexible all-solid-state energy storage devices. [ABSTRACT FROM AUTHOR]

Trimetallic sulfide microspheres with flower morphology prepared based on novel bimetallic MOF via sequential ion exchange processes exhibit promising energy storage properties. Rational design of electrical active materials with high performance for energy storage and conversion is of great significance. Herein, Cu(NiCo) 2 S 4 /Ni 3 S 4 , a three-dimensional (3D) hierarchical hollow heterostructured electrode material, is designed by etching the well-defined bimetal organic framework (MOF) via sequential in-situ ion-exchange processes. This trimetallic sulfides with unique structure provide large surface area, hierarchical pore distribution and enhanced electrical conductivity, can enrich the active sites for redox reactions, facilitate electrolyte penetration and rapid charge transfer kinetics. As a result, the Cu(NiCo) 2 S 4 /Ni 3 S 4 electrode exhibits a high specific capacitance of 1320 F/g at 1 A/g and excellent rate performance (only 15% of capacitance is attenuated when the current density is increased by 20 times). Furthermore, a fabricated hybrid supercapacitor of Cu(NiCo) 2 S 4 /Ni 3 S 4 /AC can deliver a maximum energy density of 40.8 Wh/kg, remarkable power density of 7859.2 W/kg and superior cycling stability (85% retention of capacitance after 5000 cycles), demonstrating great potential for practical applications in energy storage and conversion devices. [ABSTRACT FROM AUTHOR]

Compressible and flexible supercapacitors have aroused enormous interest of many scientific researchers for potential applications in wearable electronic products. However, the design and construction of the electrode with superior mechanical as well as electrical properties still face a lot of challenges. In present work, melamine foam/polypyrrole (MF/PPy) electrode with high deformation-tolerance and excellent electrochemical performance is prepared by in-situ interfacial polymerization of polypyrrole on commercial melamine foam, where PPy nanoparticles with size of 700 nm are uniformly anchored on the MF skeletons. The electrochemical characterizations show that the electrode exhibits excellent specific area capacitance of 2.685 F cm−2 at 2 mA cm−2 and good cyclic stability with more than 80% of capacitance remained after 3000 cycles. Furthermore, a symmetrical aqueous supercapacitor is assembled and exhibits an excellent energy density up to 75.95 μWh cm−2 at the power density of 5.82 mW cm−2 and excellent cycling stability as the current density increases by 10 times. Even under a high strain of 70%, about 95.76% of the initial capacitance is retained after 500 consecutive compressions. These outstanding performances enable the MF/PPy composite a promising candidate for potential applications in compressible and flexible electrochemical energy storage devices. [ABSTRACT FROM AUTHOR]

Nanostructured carbon materials have shown promising applications for energy storage because of their high capacitive characteristic. However, developing three-dimensional (3D) hierarchical carbon materials with both high compressibility and capacitance is still challenging. Herein, we report the fabrication of hierarchical polypyrrole (PPy)/graphene (reduced graphene oxide (G) and holey reduced graphene oxide (h-G))/melamine composite foam through a simple template method. By systematically optimizing the mass ratios of the G/h-G and the sizes of the PPy nanoparticles (PPy NPs), the as-prepared composite electrode displays a gravimetric capacitance of 422.6 F g−1 at a current density of 0.5 A g−1. Due to the interconnected h-G/G network and elastic melamine foam (MF) skeleton, the as-prepared composite electrode also shows compressible performance, which can be compressed to a strain of 60% and completely recover to its original shape when released. When the composite electrodes are assembled to a compressible supercapacitor which shows a stable capacitance under different compressive strains (0%, 25%, 50% and 75%) and a long-term compression test at 50% strain for 100 cycles. Therefore, the successful preparation of compressible composite electrode should open many opportunities in compressible and durable energy storage devices. Three dimension (3D) hierarchical PPy/graphene/melamine foam composite electrodes are fabricated for the assembly of highly compressible supercapacitor which exhibits stable electrochemical performance under different compressive strains (0%, 25%, 50% and 75%) or after 100 compression/release cycles under a compressive strain of 50%. Image 1 • 3D hierarchical composite electrode was obtained through a template method. • Connected rGO network renders the electrode with high compressibility. • PPy and the hierarchical structure makes the electrode with high capacitance. • The compressible SCs show good reliability under different compressive states. [ABSTRACT FROM AUTHOR]