Vanadium‐Based Nanomaterials: A Promising Family for Emerging Metal‐Ion Batteries

The emerging electrochemical energy storage systems beyond Li‐ion batteries, including Na/K/Mg/Ca/Zn/Al‐ion batteries, attract extensive interest as the development of Li‐ion batteries is seriously hindered by the scarce lithium resources. During the past years, large amounts of studies have focused on the investigation of various electrode materials toward emerging metal‐ion batteries to realize high energy density, high power density, and a long cycle life. In particular, vanadium‐based nanomaterials have received great attention. Vanadium‐based compounds have a big family with different structures, chemical compositions, and electrochemical properties, which provide huge possibilities for the development of emerging electrochemical energy storage. In this review, a comprehensive overview of the recent progresses of promising vanadium‐based nanomaterials for emerging metal‐ion batteries is presented. The vanadium‐based materials are classified into four groups: vanadium oxides, vanadates, vanadium phosphates, and oxygen‐free vanadium‐based compounds. The structures, electrochemical properties, and modification strategies are discussed. The structure–performance relationships and charge storage mechanisms are focused on. Finally, the perspectives about future directions of vanadium‐based nanomaterials for emerging energy storage devices are proposed. This review will provide comprehensive knowledge of vanadium‐based nanomaterials and shed light on their potential applications in emerging energy storage.     

General Formation of MS (M = Ni,Cu, Mn) Box‐in‐Box Hollow Structures with Enhanced Pseudocapacitive Properties

Complex hollow structures of metal sulfides could be promising materials for energy storage devices such as supercapacitors and lithium‐ion batteries. However, it is still a great challenge to fabricate well‐defined metal sulfides hollow structures with multi‐shells, hierarchical architectures, and non‐spherical shape. In this work, a template‐engaged strategy is developed to synthesize hierarchical NiS box‐in‐box hollow structures with double‐shells. The NiS box‐in‐box hollow structures constructed by ultrathin nanosheets are evaluated as electrode materials for supercapacitors. As expected, the NiS box‐in‐box hollow structures exhibit excellent rate performance and impressive cycling stability due to their unique nano‐architecture. More importantly, the synthetic method can be easily extended to synthesize other transition metal sulfides box‐in‐box hollow structures. For example, we have also successfully synthesized similar CuS and MnS box‐in‐box hollow structures. The present work makes a significant contribution to the design and synthesis of transition metal sulfides hollow structures with non‐spherical shape and complex architecture, as well as their potential applications in electrochemical energy storage.     

Porous Carbons Derived from Collagen‐Enriched Biomass: Tailored Design,Synthesis, and Application in Electrochemical Energy Storage and Conversion

As byproducts of the meat‐processing industry, nearly 100 million tons of bones, skin, and scales are generated from livestock, poultry, and fish every year and are generally discarded as waste. However, these widespread and low‐cost biomass materials are rich in collagen that is primarily composed of the elements C, N, O, and S. By controlled pyrolysis, these collagen‐enriched biomass materials can be transformed into biomass‐derived porous carbons (BPCs). The ordered biotic structures and specific elemental compositions of the natural precursors endow BPCs with unique nanostructures and heteroatom doping, leading to promising applications in electrochemical energy storage and conversion. In particular, BPCs derived from animal bones and fish scales show novel porosities and morphologies due to their abundance of hydroxyapatite crystals, which act as naturally occurring nanostructured templates. Here, the first review focusing on the design and synthesis of collagen‐derived porous carbons (CPCs) is given. The specific applications of different CPCs in electrochemical energy storage and conversion are also summarized. Finally, the challenges and prospects for the controllable synthesis and large‐scale applications of CPCs are assessed.     

Recent Developments of Planar Micro‐Supercapacitors: Fabrication,Properties, and Applications

The increasing development of wearable, portable, implantable, and highly integrated electronic devices has led to an increasing demand for miniaturization of energy storage devices. In recent years, supercapacitors, as an energy storage device, have received enormous attention owing to their excellent properties of quick charge and discharge, high power density, and long life cycle with minimal maintenance. Micro‐supercapacitors (MSCs) as a promising candidate for miniaturized energy storage components have undergone considerable theoretical and experimental investigations. Particularly, planar MSCs with a 2D architecture design have more attractive application prospects due to their flexible design and excellent electrochemical performance. However, the major drawbacks of MSCs are their intrinsically low energy density. For this reason, researchers have conducted much investigation to improve their energy density in order to promote their practical application. Herein, the recent development and progress of planar MSCs from the scope of the substrates, electrode materials, fabrication methods, electrochemical properties, and applications are discussed. Finally, the currently existing challenges and developments associated with planar MSCs are also discussed. All in all, planar MSCs have great application potential in various fields of electrochemical energy storage, self‐powered wireless sensors, and stimuli‐responsive and photoresponsive, alternating current line filtering.     

Wood‐Derived Lightweight and Elastic Carbon Aerogel for Pressure Sensing and Energy Storage

Lightweight and elastic carbon materials have attracted great interest in pressure sensing and energy storage for wearable devices and electronic skins. Wood is the most abundant renewable resource and offers green and sustainable raw materials for fabricating lightweight carbon materials. Herein, a facile and sustainable strategy is proposed to fabricate a wood‐derived elastic carbon aerogel with tracheid‐like texture from cellulose nanofibers (CNFs) and lignin. The flexible CNFs entangle and assemble into an interconnected framework, while lignin with high thermal stability and favorable stiffness prevents the framework from severe structural shrinkage during annealing. This strategy leads to an ordered tracheid‐like structure and significantly reduces the thermal deformation of the CNFs network, producing a lightweight and elastic carbon aerogel. The wood‐derived carbon aerogel exhibits excellent mechanical performance, including high compressibility (up to 95% strain) and fatigue resistance. It also reveals high sensitivity at a wide working pressure range of 0–16.89 kPa and can detect human biosignals accurately. Moreover, the carbon aerogel can be assembled into a flexible and free‐standing all‐solid‐state symmetric supercapacitor that reveals satisfactory electrochemical performance and mechanical flexibility. These features make the wood‐derived carbon aerogel highly attractive for pressure sensor and flexible electrode applications.     

Tungsten‐Based Materials for Lithium‐Ion Batteries

Lithium‐ion batteries are widely used as reliable electrochemical energy storage devices due to their high energy density and excellent cycling performance. The search for anode materials with excellent electrochemical performances remains critical to the further development of lithium‐ion batteries. Tungsten‐based materials are receiving considerable attention as promising anode materials for lithium‐ion batteries owing to their high intrinsic density and rich framework diversity. This review describes the advances of exploratory research on tungsten‐based materials (tungsten oxide, tungsten sulfide, tungsten diselenide, and their composites) in lithium‐ion batteries, including synthesis methods, microstructures, and electrochemical performance. Some personal prospects for the further development of this field are also proposed.     

Porous Iron–Cobalt Alloy/Nitrogen‐Doped Carbon Cages Synthesized via Pyrolysis of Complex Metal–Organic Framework Hybrids for Oxygen Reduction

Efficient and stable nonprecious metal electrocatalysts for oxygen reduction are of great significance in some important electrochemical energy storage and conversion systems. As a unique class of porous hybrid materials, metal–organic frameworks (MOFs) and their composites are recently considered as promising precursors to derive advanced functional materials with controlled structures and compositions. Here, an “MOF‐in‐MOF hybrid” confined pyrolysis strategy is developed for the synthesis of porous Fe–Co alloy/N‐doped carbon cages. A unique “MOF‐in‐MOF hybrid” architecture constructed from a Zn‐based MOF core and a Co‐based MOF hybrid shell encapsulated with FeOOH nanorods is first prepared, followed by a pyrolysis process to obtain a cage‐shaped hybrid material consisting of Fe–Co alloy nanocrystallites evenly distributed inside a porous N‐doped carbon microshell. Of note, this strategy can be extended to synthesize many other multifunctional “nanosubstrate‐in‐MOF hybrid” core–shelled structures. Benefiting from the structural and compositional advantages, the as‐derived hybrid cages exhibit superior electrocatalytic performance for the oxygen reduction reaction in alkaline solution. The present approach may provide some insight in design and synthesis of complex MOF hybrid structures and their derived functional materials for energy storage and conversion applications.     

Recent Progress in Synthesis and Application of Biomass-Based Hybrid Electrodes for Rechargeable Batteries

The rapid growth in electronic and portable devices demands safe, durable, light weight, low cost, high energy, and power density electrode materials for rechargeable batteries. In this context, biomass-based materials and their hybrids are extensively used for energy generation research, which is primarily due to their properties such as large specific surface area, fast ion/electron kinetics, restricted volume expansion, and restrained shuttle effect. In this review, the key advancements in the preparation of biomass derived porous carbons using different synthesis strategies and their modifications with species such as heteroatoms, metal oxides, metal sulfides, silicon, and other carbon forms are discussed. The electrochemical performances of these materials and the ion storage mechanisms in different batteries including lithium-ion, lithium–sulfur, sodium-ion, and potassium-ion batteries are discussed. Special attention will be paid to the challenges in using porous biomass-derived carbons and the current strategies employed for maximizing the specific capacity and lifetime for battery applications. Finally, the drawbacks in current technology and endeavors for the future research and development in the field to catapult the performances of the biomass derived materials in order to equip them to meet the demands of commercialization are highlighted.     

Ultrathin Nickel–Cobalt Phosphate 2D Nanosheets for Electrochemical Energy Storage under Aqueous/Solid‐State Electrolyte

2D materials are ideal for constructing flexible electrochemical energy storage devices due to their great advantages of flexibility, thinness, and transparency. Here, a simple one‐step hydrothermal process is proposed for the synthesis of nickel–cobalt phosphate 2D nanosheets, and the structural influence on the pseudocapacitive performance of the obtained nickel–cobalt phosphate is investigated via electrochemical measurement. It is found that the ultrathin nickel–cobalt phosphate 2D nanosheets with an Ni/Co ratio of 4:5 show the best electrochemical performance for energy storage, and the maximum specific capacitance up to 1132.5 F g^?1. More importantly, an aqueous and solid‐state flexible electrochemical energy storage device has been assembled. The aqueous device shows a high energy density of 32.5 Wh kg^?1 at a power density of 0.6 kW kg^?1, and the solid‐state device shows a high energy density of 35.8 Wh kg^?1 at a power density of 0.7 kW kg^?1. These excellent performances confirm that the nickel–cobalt phosphate 2D nanosheets are promising materials for applications in electrochemical energy storage devices.     

Flexible energy storage devices for wearable bioelectronics

With the growing market of wearable devices for smart sensing and personalized healthcare applications,energy stor-age devices that ensure stable power supply and can be constructed in flexible platforms have attracted tremendous research in-terests.A variety of active materials and fabrication strategies of flexible energy storage devices have been intensively studied in recent years,especially for integrated self-powered systems and biosensing.A series of materials and applications for flex-ible energy storage devices have been studied in recent years.In this review,the commonly adopted fabrication methods of flex-ible energy storage devices are introduced.Besides,recent advances in integrating these energy devices into flexible self-powered systems are presented.Furthermore,the applications of flexible energy storage devices for biosensing are summar-ized.Finally,the prospects and challenges of the self-powered sensing system for wearable electronics are discussed.     

Self-Supporting Electrodes for Gas-Involved Key Energy Reactions

Self-supporting materials are widely adopted in gas-involved electrocatalysis during the past few decades because of their unique physical/electrochemical properties, especially the stabilized spatial framework and the large electrochemical interfaces. Reportedly, there is no clear definition to define “self-supporting” materials, and also, no such comprehensive reviews have fully discussed the self-supporting materials in gas-involved electrochemical applications. Therefore, it is necessary to provide timely updates in this potential field. In this review, for the first time, a reasonable definition of self-supporting materials and comprehensively review the recent research progress of related electrodes in gas-involved electrocatalytic applications is given. Firstly, it is discussed their synthetic methodologies, including design principles, different types of substrates- and substrate-free structures. Subsequently, the recent advances of self-supporting electrodes for gas-involved key energy related electrocatalysis (i.e., hydrogen evolution, oxygen reduction, oxygen evolution, nitrogen reduction, and carbon dioxide reduction reactions) and their practical applications in water-splitting, fuel cells and metal-air batteries are mainly presented. Finally, a summary of the progress of self-supporting electrocatalysts, the remaining challenges, and the perspectives are given to instruct their future development. It is expected that this review will provide new research insights for the future development of renewable energy storage and conversion systems.     

Advances on Emerging Materials for Flexible Supercapacitors: Current Trends and Beyond

The progressive size reduction of electronic components is experiencing bottlenecks in shrinking charge storage devices like batteries and supercapacitors, limiting their development into wearable and flexible zero‐pollution technologies. The inherent long cycle life, rapid charge–discharge patterns, and power density of supercapacitors rank them superior over other energy storage devices. In the modern market of zero‐pollution energy devices, currently the lightweight formula and shape adaptability are trending to meet the current requirement of wearables. Carbon nanomaterials have the potential to meet this demand, as they are the core of active electrode materials for supercapacitors and texturally tailored to demonstrate flexible and stretchable properties. With this perspective, the latest progress in novel materials from conventional carbons to recently developed and emerging nanomaterials toward lightweight stretchable active compounds for flexi‐wearable supercapacitors is presented. In addition, the limitations and challenges in realizing wearable energy storage systems and integrating the future of nanomaterials for efficient wearable technology are provided. Moreover, future perspectives on economically viable materials for wearables are also discussed, which could motivate researchers to pursue fabrication of cheap and efficient flexible nanomaterials for energy storage and pave the way for enabling a wide‐range of material‐based applications.     

Recent Progress in Advanced Organic Electrode Materials for Sodium‐Ion Batteries: Synthesis,Mechanisms, Challenges and Perspectives

Rechargeable sodium‐ion batteries (SIBs) are considered attractive alternatives to lithium‐ion batteries for next‐generation sustainable and large‐scale electrochemical energy storage. Organic sodium‐ion batteries (OSIBs) using environmentally benign organic materials as electrodes, which demonstrate high energy/power density and good structural designability, have recently attracted great attention. Nevertheless, the practical applications and popularization of OSIBs are generally restricted by the intrinsic disadvantages related to organic electrodes, such as their low conductivity, poor stability, and high solubility in electrolytes. Here, the latest research progress with regard to electrode materials of OSIBs, ranging from small molecules to organic polymers, is systematically reviewed, with the main focus on the molecular structure design/modification, the electrochemical behavior, and the corresponding charge‐storage mechanism. Particularly, the challenges faced by OSIBs and the effective design strategies are comprehensively summarized from three aspects: function‐oriented molecular design, micromorphology regulation, and construction of organic–inorganic composites. Finally, the perspectives and opportunities in the research of organic electrode materials are discussed.     

The Applications of Water-in-Salt Electrolytes in Electrochemical Energy Storage Devices

Water-in-salt electrolytes (WISEs) have attracted widespread attention due to their non-flammability, environmental friendliness, and wider electrochemical stability window than conventional dilute aqueous electrolytes. When applied in the electrochemical energy storage (EES) devices, WISEs can offer many advantages such as high-level safety, manufacturing efficiency, as well as, superior electrochemical performances. Therefore, there is an urgent need for a timely and comprehensive summary of WISEs and their EES applications. In this review, the physicochemical and electrochemical properties of the WISEs are first introduced. Then, the research progresses of the WISEs using different metal salts and their analogues are summarized. Next, the current research progresses of WISEs applied in different EES devices (e.g., batteries and supercapacitors) as well as the insights into challenging and future perspectives are systematically discussed.     

Colossal Permittivity Materials as Superior Dielectrics for Diverse Applications

Ever since the beginning of this century, many kinds of materials have been reported to demonstrate colossal permittivity (CP) or a colossal dielectric constant exceeding 10³. Accordingly, such CP materials and their further modification and improvement to achieve enhanced CP performance for promising applications in modern electronics, sensors, energy storage, and multifunctional devices have attracted extensive attention. In this Review, a general overview of the recent advances in CP materials is provided, ranging from their various categories, physical mechanisms, and modulation methods to promising applications. First, various classes of CP materials are categorized in terms of their structures and dielectric properties. Subsequently, this Review provides an insight into the CP mechanisms in views of barrier layer capacitance, defect‐dipole cluster, and polaronic effect. Moreover, the strategies and prototypical works are introduced in some aspects, including the manipulation of CP properties by doping, percolative capacitors, and the methods employed to enhance the dielectric behaviors in CP materials with different forms. The authors then discuss a wide range of applications based on CP materials, such as modern electronics and energy storage. Finally, the challenges and opportunities for further investigation of CP materials are highlighted in the summary and future perspectives.     

Advanced Exfoliation Strategies for Layered Double Hydroxides and Applications in Energy Conversion and Storage

Along with the increasing aggravation of energy and environmental problems, the demand and utilization of renewable energy have increased. The rational design of advanced functional materials serves as a critical point for the improvement of performance and the practical application in renewable energy devices. Layered double hydroxides (LDHs) with 2D layered structures are promising energy materials for their unique physical and chemical properties. Nevertheless, the applications are limited by the structure of stacking with irrational electronic structure, sluggish mass transfer, and low activity. The exfoliation of LDHs into single‐ or few‐layered nanosheets appears to be a promising approach to overcome the above disadvantages. Herein, the recent progress on the development of exfoliation strategies for LDHs including liquid phase exfoliation, plasma‐induced exfoliation, and other advanced exfoliation strategies is highlighted and the applications in energy conversion and storage are systematically introduced.     

铋烯材料生长控制及光电子器件应用研究进展

石墨烯和其他二维材料凭借其自身独特的物理和化学性能,引起了科学和工程领域的广泛关注。探索新型二维材料体系并扩展其应用范围是研究人员的热点研究内容。其中,第五主族单元素二维烯(二维磷烯、二维砷烯、二维锑烯、二维铋烯)具有较窄的且可调节的能带宽度、高的载流子迁移率、良好的透光性和优异的光电子学性能,成为二维材料及其在光电子应用领域的新的研究对象。鉴于此方面,从基本物理结构、材料的制备方法和在光电子方面的应用深入分析二维铋烯的相关理论以及实验研究的工作进展。在材料的可控制备方面,重点围绕二维铋烯的电化学剥离法展开相应论述。最后讨论了二维铋烯在光电子学应用领域的现状,包括在超快光电子学器件的应用,并且对二维铋烯未来的发展进行了展望。     

Leaf‐like Graphene Oxide with a Carbon Nanotube Midrib and Its Application in Energy Storage Devices

Graphene oxide (GO) has recently attracted a great deal of attention because of its heterogeneous chemical and electronic structures and its consequent exhibition of a wide range of potential applications, such as plastic electronics, optical materials, solar cells, and biosensors. However, its insulating nature also limits its application in some electronic and energy storage devices. In order to further widen the applications of GO, it is necessary to keep its inherent characteristics while improving its conductivity. Here, a novel leaf‐like GO with a carbon nanotube (CNT) midrib is developed using vapor growth carbon fiber (VGCF) through the conventional Hummers method. The CNT midrib provides a natural electron diffusion path for the leaf‐like GO, and therefore, this leaf‐like GO with a CNT midrib displays excellent performance when applied in energy storage devices, including Li‐O₂ batteries, Li‐ion batteries, and supercapacitors.     

Engineering the Thermal Conductivity of Functional Phase‐Change Materials for Heat Energy Conversion,Storage, and Utilization

Thermal energy storage technologies based on phase‐change materials (PCMs) have received tremendous attention in recent years. These materials are capable of reversibly storing large amounts of thermal energy during the isothermal phase transition and offer enormous potential in the development of state‐of‐the‐art renewable energy infrastructure. Thermal conductivity plays a vital role in regulating the thermal charging and discharging rate of PCMs and improving the heat‐utilization efficiency. The strategies for tuning the thermal conductivity of PCMs and their potential energy applications, such as thermal energy harvesting and storage, thermal management of batteries, thermal diodes, and other forms of energy utilization, are summarized systematically. Furthermore, a research perspective is given to highlight emerging research directions of engineering advanced functional PCMs for energy applications.     

Large‐Area Reduced Graphene Oxide Composite Films for Flexible Asymmetric Sandwich and Microsized Supercapacitors

Asymmetric supercapacitors have attracted tremendous attention in energy storage devices since they have an enhanced energy density in comparison with symmetric supercapacitor devices. Furthermore, the development of diverse and flexible electronic devices requires the asymmetric supercapacitor devices to be flexible and in various configurations. However, it is still a challenge to develop a universal strategy to obtain both capacitive and Faradic electrodes with various architectures. Herein, a spontaneously reducing/assembling strategy in an alkaline condition is developed to fabricate large‐area reduced graphene oxide (RGO) and RGO–metal oxide/hydroxide composite films or microsized structures. As a proof of concept, the large‐area pure RGO and RGO/Mn₃O₄ composite films with porous structure and superior mechanical property are achieved by such strategy. These RGO‐based films can directly serve as the anodes and cathodes of the flexible asymmetric film supercapacitors. Furthermore, the interdigital RGO and RGO/Mn₃O₄ patterns are also obtained via a selectively reducing/assembling process to achieve the asymmetric microsized supercapacitors. These asymmetric supercapacitors with different configurations possess good electrochemical performance and excellent flexibility. Therefore, such reducing and assembling strategy provides a route to achieve large‐area RGO‐based films and microsized structures for the applications in the various fields such as energy storage and photocatalysis.