MXenes for advanced separator in rechargeable batteries

As an indispensable part of electric devices, separator play a key role in electrochemical performance. Thus, separator engineering is a promising way of constructing better energy storage and conversion systems. MXenes, a novel class of 2D transition metal nitrides, carbides, and carbonitrides, are emerging for separator engineering due to their unique properties, such as high conductivity, large surface area, controllable hydrophilicity, abundant surface chemistries, and superior mechanical performance. The related investigations have remarkably increased since 2020. However, comprehensive reviews on this topic are rare. Herein, an overview of MXenes in separator engineering for rechargeable batteries is systematically presented. Firstly, the fundamental principles of MXenes, including composition, synthesis techniques, and functionalization, are summarized. Subsequently, the basic information on separator design and its optimization is introduced. Finally, the applications of MXenes for separator engineering and their applications in rechargeable batteries are reviewed. In the end, the perspectives and challenges on the further development of MXenes-based separators in rechargeable batteries are proposed. This review will help researchers in the design and construction of functional separators for batteries, supercapacitors, fuel cells, etc.     

MXenes for Rechargeable Batteries Beyond the Lithium‐Ion

Research on next‐generation battery technologies (beyond Li‐ion batteries, or LIBs) has been accelerating over the past few years. A key challenge for these emerging batteries has been the lack of suitable electrode materials, which severely limits their further developments. MXenes, a new class of 2D transition metal carbides, carbonitrides, and nitrides, are proposed as electrode materials for these emerging batteries due to several desirable attributes. These attributes include large and tunable interlayer spaces, excellent hydrophilicity, extraordinary conductivity, compositional diversity, and abundant surface chemistries, making MXenes promising not only as electrode materials but also as other components in the cells of emerging batteries. Herein, an overview and assessment of the utilization of MXenes in rechargeable batteries beyond LIBs, including alkali‐ion (e.g., Na⁺, K⁺) storage, multivalent‐ion (e.g., Mg²⁺, Zn²⁺, and Al³⁺) storage, and metal batteries are presented. In particular, the synthetic strategies and properties of MXenes that enable MXenes to play various roles as electrodes, metal anode protective layers, sulfur hosts, separator modification layers, and conductive additives in these emerging batteries are discussed. Moreover, a perspective on promising future research directions on MXenes and MXene‐based materials, ranging from material design and processing, fundamental understanding of the reaction mechanisms, to device performance optimization strategies is provided.     

A review on the stability and surface modification of layered transition-metal oxide cathodes

An ever-increasing market for electric vehicles (EVs), electronic devices and others has brought tremendous attention on the need for high energy density batteries with reliable electrochemical performances. However, even the successfully commercialized lithium (Li)-ion batteries still face significant challenges with respect to cost and safety issues when they are used in EVs. From a cathode material point of view, layered transition-metal (TM) oxides, represented by LiMO₂ (M = Ni, Mn, Co, Al, etc.) and Li-/Mn-rich xLi₂MnO₃·(1–x)LiMO₂, have been considered as promising candidates because of their high theoretical capacity, high operating voltage, and low manufacturing cost. However, layered TM oxides still have not reached their full potential for EV applications due to their intrinsic stability issues during electrochemical processes. To address these problems, a variety of surface modification strategies have been pursued in the literature. Herein, we summarize the recent progresses on the enhanced stability of layered TM oxides cathode materials by different surface modification techniques, analyze the manufacturing process and cost of the surface modification methods, and finally propose future research directions in this area.     

Metal organic framework (MOF) in aqueous energy devices

Aqueous energy devices are under the spotlight of current research due to their safety, low cost and ease of handling. Metal-organic frameworks (MOFs) and their derivatives have spurred extensive exploration as they provide a library of new electrode materials. The rich and structural flexibilities (such as metal nodes, ligands, pore structure) endow MOFs and MOFs-derivatives with vast opportunities for various energy devices. In this review, we discuss the correlation between MOF structural parameters and electrochemical performance for aqueous energy devices in the scope of zinc-based batteries (Zn-ion, Zn-alkaline and Zn-air batteries), potassium-ion batteries and supercapacitors. For each energy device, the effect of determinative factors and structural modulating strategies of MOFs and derivatives are highlighted. Finally, we summarize the challenges and provide our perspective about MOFs and derivatives for future aqueous energy devices.     

Ti基MXene及其复合材料在金属离子电池中的进展

二维过渡金属碳(氮或碳氮)化物MXene自2011年首次报告后,其家族成员不断增加,目前已有超过20种MXene被成功合成。凭借独特的层状结构,出色的物理化学性质和可设计的表面官能团特性,MXene被认为是极具潜力的电极材料。近年来,MXene及其复合材料在储能领域进展显著。为此,本文综述了Ti基MXene及其复合材料在Li离子电池和Na离子电池中的研究进展,并结合其制备方法和特性,详细介绍了电池性能提升策略或机制。最后,指出了MXene及其复合材料构建高性能电池面临的挑战,并对未来前景进行了展望。      

Advances and issues in developing intercalation graphite cathodes for aqueous batteries

Aqueous rechargeable batteries offer a safe alternative for electrochemical energy storage, integrating cost-efficiency and energy density to meet the demand for stationary applications. Recent efforts have focused on the improvement of electrode materials in aqueous electrolytes, particularly the cycle life and energy reliability of batteries. The anion intercalation chemistry in graphite could be an alternative cathode candidate, often requiring an upper cut-off potential above 4.5 V vs. Li⁺/Li. Such a potential readily exceeds the electrochemical stability windows of water-based electrolytes. Herein, we provide a progress report and critical comment on the reversible intercalation chemistry in graphite compounds, i.e., anion and halogen intercalations, for the development of economical, high-energy aqueous rechargeable batteries. In addition, this review focuses on the charge carrier species, their charge storage mechanisms and battery configurations, aiming to provide solutions to solve the remaining key challenges for aqueous batteries.     

Emerging applications of MXenes for photodetection: Recent advances and future challenges

The development and applications of transition metal carbides, nitrides and carbonitrides, commonly denoted as MXenes, have during the last few years rapidly expanded in various technological fields owing to their unique and controllable properties. These materials exhibit competing performance comparing with traditional materials and have created numerous opportunities for technology markets. Taking the advantage of excellent optoelectronic features, MXenes have been utilized for the construction of photodetectors with various structures and unique functionalities. While the application of MXenes in this area can be traced back to 2016, we have during the recent three years witnessed a dramatic development of MXene-based photodetectors, calling for a timely review to guideline their future direction. In this work, synthetic strategies of pristine MXenes are briefly introduced and their properties are discussed focusing on the optoelectronic aspects that are fundamental for the photoelectric conversion. Recent advances of MXene-based photodetectors are comprehensively summarized based on different types of MXenes and innovative designs of device construction. Finally, we provide perspectives for future challenges and opportunities of MXene-based photodetectors, which may enlighten their further development.     

Advanced polyanionic electrode materials for potassium-ion batteries: Progresses,challenges and application prospects

Although potassium-ion batteries (KIBs) are considered a very promising energy storage system, their development for actual application still has a long way to go. Advanced electrode materials, as a fundamental component of KIBs, are essential for optimizing electrochemical performance and promoting effective energy storage. Due to their unique structural benefits in terms of cycle capability, strong ionic conductivity, and tunable operating voltage, polyanionic compounds are one type of viable electrode material for manufacturing high-performance KIBs. The huge size of K⁺ ion, on the other hand, places great demands on polyanionic materials, which must be able to withstand severe structural deformation during K⁺ intercalation/delamination. To maintain steady electrochemical performance, it is critical to follow the appropriate design guidelines for electrode materials. This paper provides a summary of current advancements in polyanionic compound for KIBs, with a focus on electrode material structural design. The effects of various parameters on electrochemical performance are examined and summarized. In addition, various viable solutions are proposed to address the impending issues posed by polyanionic compounds for KIBs, with the hope of providing a clearer picture of the field's future development path.     

Catalytic effect in Li-S batteries: From band theory to practical application

Lithium-sulfur (Li-S) batteries with high energy density have been considered one kind of promising next-generation energy storage system. However, the shuttling effect of polysulfides caused by the intrinsic sluggish reaction kinetics severely hinders their commercialization. The catalytic effect, a powerful solution towards polysulfides shuttling by accelerating the conversion of polysulfides, has aroused great attention. Numerous catalysts have been developed and proved to have catalytic effects in the past years. More importantly, many advanced in-situ characterization technologies and electronic structure analyses have been combined to study the “black box” of the catalytic process, which promotes the practical application of Li-S batteries entering a new stage. In this review, instead of summarizing recent achievements in catalyst materials and structural designs, the key issues that how to observe, understand, design, and use catalytic effect in Li-S batteries are systematically discussed. In-situ techniques are summarized to see the actual catalytic process. Band theory is applied to understand the electronic structure, thus deciphering design principles and strategies of catalytic effect. Subsequently, how to use the catalytic effect to realize Ah-level Li-S pouch cells is analyzed. Last, we propose a research paradigm for catalytic effect, which will enlighten the future development of Li-S batteries and other next-generation batteries based on conversion reactions.     

Layered Transition Metal Dichalcogenide-Based Nanomaterials for Electrochemical Energy Storage

The rapid development of electrochemical energy storage (EES) systems requires novel electrode materials with high performance. A typical 2D nanomaterial, layered transition metal dichalcogenides (TMDs) are regarded as promising materials used for EES systems due to their large specific surface areas and layer structures benefiting fast ion transport. The typical methods for the preparation of TMDs and TMD-based nanohybrids are first summarized. Then, in order to improve the electrochemical performance of various kinds of rechargeable batteries, such as lithium-ion batteries, lithium–sulfur batteries, sodium-ion batteries, and other types of emerging batteries, the strategies for the design and fabrication of layered TMD-based electrode materials are discussed. Furthermore, the applications of layered TMD-based nanomaterials in supercapacitors, especially in untraditional supercapacitors, are presented. Finally, the existing challenges and promising future research directions in this field are proposed.     

水溶液钠离子电池及其关键材料的研究进展

钠离子电池具有资源与成本等方面明显的优势, 正成为新一代储能技术的发展热点。对于大规模、固定式储能场合, 水溶液钠离子电池更为安全可靠、价格低廉、环境友好, 理论上具有广泛的应用前景。然而, 水溶液钠离子电池在材料选择和应用方面所面临的问题也非常复杂。针对这些问题, 本文简要分析了水系储钠材料与电极反应的特殊性, 介绍了水系钠离子电池的研究进展, 同时结合本课题组的研究工作讨论了相关的技术发展方向。     

Emerging 2D Copper-Based Materials for Energy Storage and Conversion: A Review and Perspective

2D materials have shown great potential as electrode materials that determine the performance of a range of electrochemical energy technologies. Among these, 2D copper-based materials, such as Cu–O, Cu–S, Cu–Se, Cu–N, and Cu–P, have attracted tremendous research interest, because of the combination of remarkable properties, such as low cost, excellent chemical stability, facile fabrication, and significant electrochemical properties. Herein, the recent advances in the emerging 2D copper-based materials are summarized. A brief summary of the crystal structures and synthetic methods is started, and innovative strategies for improving electrochemical performances of 2D copper-based materials are described in detail through defect engineering, heterostructure construction, and surface functionalization. Furthermore, their state-of-the-art applications in electrochemical energy storage including supercapacitors (SCs), alkali (Li, Na, and K)-ion batteries, multivalent metal (Mg and Al)-ion batteries, and hybrid Mg/Li-ion batteries are described. In addition, the electrocatalysis applications of 2D copper-based materials in metal–air batteries, water-splitting, and CO₂ reduction reaction (CO₂RR) are also discussed. This review also discusses the charge storage mechanisms of 2D copper-based materials by various advanced characterization techniques. The review with a perspective of the current challenges and research outlook of such 2D copper-based materials for high-performance energy storage and conversion applications is concluded.     

Rational design of MXene-based films for energy storage: Progress,prospects

Two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides (MXenes) have been synthesized and developed into a wide range of applications including energy storage, optoelectronics, electromagnetic interference shielding, biomedicine, and sensors, etc. Compared to other 2D materials, MXenes possess a unique set of properties such as superior mechanical strength, outstanding hydrophily, and excellent dispersion quality, making them particularly suitable for fabricating films/membranes featuring designed microstructures and tunable nanochannels. 2D MXene-based films (MBFs) have demonstrated excellent ion storage, electron transport and ionic selectivity properties for electrochemical energy storage and have received enormous interest in recent years. Compared with conventional electrode materials and structures, MBFs show great advantages in the aspects of flexibility, tailorability and functionality, which are suitable for flexible, portable, and highly integrated energy storage systems. This review summarizes recent advances and well-developed strategies of the MBFs design and fabrication toward applications of metal-ion batteries (MIBs, including Li, Na, K-ions), lithium-sulfur (Li-S) batteries and supercapacitors (SCs). Special attentions are given to the design principles of MBFs based microstructures, inter-layer nanochannels and in-plane nanochannels for energy storage. Finally, the current challenges and promising perspectives of the MBFs for energy storage devices are presented.     

Hollow MXene Spheres and 3D Macroporous MXene Frameworks for Na‐Ion Storage

2D transition metal carbides and nitrides, named MXenes, are attracting increasing attentions and showing competitive performance in energy storage devices including electrochemical capacitors, lithium‐ and sodium‐ion batteries, and lithium–sulfur batteries. However, similar to other 2D materials, MXene nanosheets are inclined to stack together, limiting the device performance. In order to fully utilize MXenes' electrochemical energy storage capability, here, processing of 2D MXene flakes into hollow spheres and 3D architectures via a template method is reported. The MXene hollow spheres are stable and can be easily dispersed in solvents such as water and ethanol, demonstrating their potential applications in environmental and biomedical fields as well. The 3D macroporous MXene films are free‐standing, flexible, and highly conductive due to good contacts between spheres and metallic conductivity of MXenes. When used as anodes for sodium‐ion storage, these 3D MXene films exhibit much improved performances compared to multilayer MXenes and MXene/carbon nanotube hybrid architectures in terms of capacity, rate capability, and cycling stability. This work demonstrates the importance of MXene electrode architecture on the electrochemical performance and can guide future work on designing high‐performance MXene‐based materials for energy storage, catalysis, environmental, and biomedical applications.     

Advanced Materials for Sodium‐Ion Capacitors with Superior Energy–Power Properties: Progress and Perspectives

Developing electrochemical energy storage devices with high energy–power densities, long cycling life, as well as low cost is of great significance. Sodium‐ion capacitors (NICs), with Na⁺ as carriers, are composed of a high capacity battery‐type electrode and a high rate capacitive electrode. However, unlike their lithium‐ion analogues, the research on NICs is still in its infancy. Rational material designs still need to be developed to meet the increasing requirements for NICs with superior energy–power performance and low cost. In the past few years, various materials have been explored to develop NICs with the merits of superior electrochemical performance, low cost, good stability, and environmental friendliness. Here, the material design strategies for sodium‐ion capacitors are summarized, with focus on cathode materials, anode materials, and electrolytes. The challenges and opportunities ahead for the future research on materials for NICs are also proposed.     

Borohydride‐Scaffolded Li/Na/Mg Fast Ionic Conductors for Promising Solid‐State Electrolytes

Borohydride solid‐state electrolytes with room‐temperature ionic conductivity up to ≈70 mS cm^?1 have achieved impressive progress and quickly taken their place among the superionic conductive solid‐state electrolytes. Here, the focus is on state‐of‐the‐art developments in borohydride solid‐state electrolytes, including their competitive ionic‐conductive performance, current limitations for practical applications in solid‐state batteries, and the strategies to address their problems. To open, fast Li/Na/Mg ionic conductivity in electrolytes with BH₄ ^? groups, approaches to engineering borohydrides with enhanced ionic conductivity, and later on the superionic conductivity of polyhedral borohydrides, their correlated conductive kinetics/thermodynamics, and the theoretically predicted high conductive derivatives are discussed. Furthermore, the validity of borohydride pairing with coated oxides, sulfur, organic electrodes, MgH₂, TiS₂, Li₄Ti₅O₁₂, electrode materials, etc., is surveyed in solid‐state batteries. From the viewpoint of compatible cathodes, the stable electrochemical windows of borohydride solid‐state electrolytes, the electrode/electrolyte interface behavior and battery device design, and the performance optimization of borohydride‐based solid‐state batteries are also discussed in detail. A comprehensive coverage of emerging trends in borohydride solid‐state electrolytes is provided and future maps to promote better performance of borohydride SSEs are sketched out, which will pave the way for their further development in the field of energy storage.     

Electrochemomechanical degradation of high-capacity battery electrode materials

Enormous efforts have been undertaken to develop rechargeable batteries with new electrode materials that not only have superior energy and power densities, but also are resistant to electrochemomechanical degradation despite huge volume changes. This review surveys recent progress in the experimental and modeling studies on the electrochemomechanical phenomena in high-capacity electrode materials for lithium-ion batteries. We highlight the integration of electrochemical and mechanical characterizations, in-situ transmission electron microscopy, multiscale modeling, and other techniques in understanding the strong mechanics-electrochemistry coupling during charge-discharge cycling. While anode materials for lithium ion batteries (LIBs) are the primary focus of this review, high-capacity electrode materials for sodium ion batteries (NIBs) are also briefly reviewed for comparison. Following the mechanistic studies, design strategies including nanostructuring, nanoporosity, surface coating, and compositing for mitigation of the electrochemomechanical degradation and promotion of self-healing of high-capacity electrodes are discussed.     

Rechargeable aqueous zinc-ion batteries: Mechanism,design strategies and future perspectives

Rechargeable aqueous zinc-ion batteries (ZIBs) are considered to be one of the most promising energy storage devices for grid-scale applications due to their high safety, eco-friendliness, and low cost. In recent years, enormous efforts have been devoted to developing a great number of high-efficient cathodes, anodes, and electrolytes for improving the electrochemical properties of aqueous ZIBs. However, the as-documented ZIBs and their associated energy storage mechanisms are still in infancy and need to be further investigated for real practice. To expedite the development of ZIBs, this review will offer a comprehensive summary and a detailed discussion of the significant progress and breakthroughs. A brief overview of the battery configuration and various energy storage mechanisms are first introduced. The following emphasis will be mainly dedicated to discussing different design strategies regarding cathodes, anodes, and electrolytes, aiming to provide insightful design principles for future research activities from a fundamental perspective. Finally, the current challenges of developing high-performance ZIBs and their opportunities for practical viability are discussed.     

Electrolyte formulas of aqueous zinc ion battery: A physical difference with chemical consequences

Researchers have recently redirected their attention toward aqueous batteries in pursuit of safety and affordability. The water-based electrolyte promises many appealing merits such as non-flammability and environmental friendliness but is also cursed with low energy density. In an attempt of lifting the curse, many efforts have been made to re-formulate the aqueous electrolyte, which seems unlikely to succeed without understanding the interplay between electrolytes’ physical properties and electrochemical performance. Starting from the composition of electrolytes, we discuss how various formulas of zinc ion battery electrolytes lead to diverse electrochemical performances. By evaluating the electrochemical performance of batteries in five metrics, it provides a la carte electrolyte designing strategies with different battery purposes.     

Doping Regulation in Polyanionic Compounds for Advanced Sodium-Ion Batteries

It has long been the goal to develop rechargeable batteries with low cost and long cycling life. Polyanionic compounds offer attractive advantages of robust frameworks, long-term stability, and cost-effectiveness, making them ideal candidates as electrode materials for grid-scale energy storage systems. In the past few years, various polyanionic electrodes have been synthesized and developed for sodium storage. Specifically, doping regulation including cation and anion doping has shown a great effect in tailoring the structures of polyanionic electrodes to achieve extraordinary electrochemical performance. In this review, recent progress in doping regulation in polyanionic compounds as electrode materials for sodium-ion batteries (SIBs) is summarized, and their underlying mechanisms in improving electrochemical properties are discussed. Moreover, challenges and prospects for the design of advanced polyanionic compounds for SIBs are put forward. It is anticipated that further versatile strategies in developing high-performance electrode materials for advanced energy storage devices can be inspired.