Calcium‐Ion Batteries: Current State‐of‐the‐Art and Future Perspectives

Recent developments in rechargeable battery technology have seen a shift from the well‐established Li‐ion technology to new chemistries to achieve the high energy density required for extended range electric vehicles and other portable applications, as well as low‐cost alternatives for stationary storage. These chemistries include Li–air, Li–S, and multivalent ion technologies including Mg²⁺, Zn²⁺, Ca²⁺, and Al³⁺. While Mg²⁺ battery systems have been increasingly investigated in the last few years, Ca²⁺ technology has only recently been recognized as a viable option. In this first comprehensive review of Ca²⁺ ion technology, the use of Ca metal anodes, alternative alloy anodes, electrolytes suitable for this system, and cathode material development are discussed. The advantages and disadvantages of Ca²⁺ ion batteries including prospective achievable energy density, cost reduction due to high natural abundance, low ion mobility, the effect of ion size, and the need for elevated temperature operation are reviewed. The use of density functional theory modeling to predict the properties of Ca‐ion battery materials is discussed and the extent to which this approach is successful in directing research into areas of promise is evaluated. To conclude, a summary of recent achievements is presented and areas for future research efforts evaluated.     

MOF‐Derived Metal Oxide Composites for Advanced Electrochemical Energy Storage

Over the past two decades, metal–organic frameworks (MOFs), a type of porous material, have aroused great interest as precursors or templates for the derivation of metal oxides and composites for the next generation of electrochemical energy storage applications owing to their high specific surface areas, controllable structures, and adjustable pore sizes. The electrode materials, which affect the performance in practical applications, are pivotal components of batteries and supercapacitors. Metal oxide composites derived from metal–organic frameworks possessing high reversible capacity and superior rate and cycle performance are excellent electrode materials. In this Review, potential applications for MOF‐derived metal oxide composites for lithium‐ion batteries, sodium‐ion batteries, lithium–oxygen batteries, and supercapacitors are studied and summarized. Finally, the challenges and opportunities for future research on MOF‐derived metal oxide composites are proposed on the basis of academic knowledge from the reported literature as well as from experimental experience.     

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.     

Defect Engineering on Electrode Materials for Rechargeable Batteries

The reasonable design of electrode materials for rechargeable batteries plays an important role in promoting the development of renewable energy technology. With the in-depth understanding of the mechanisms underlying electrode reactions and the rapid development of advanced technology, the performance of batteries has significantly been optimized through the introduction of defect engineering on electrode materials. A large number of coordination unsaturated sites can be exposed by defect construction in electrode materials, which play a crucial role in electrochemical reactions. Herein, recent advances regarding defect engineering in electrode materials for rechargeable batteries are systematically summarized, with a special focus on the application of metal-ion batteries, lithium–sulfur batteries, and metal–air batteries. The defects can not only effectively promote ion diffusion and charge transfer but also provide more storage/adsorption/active sites for guest ions and intermediate species, thus improving the performance of batteries. Moreover, the existing challenges and future development prospects are forecast, and the electrode materials are further optimized through defect engineering to promote the development of the battery industry.     

Structural Reorganization–Based Nanomaterials as Anodes for Lithium‐Ion Batteries: Design,Preparation, and Performance

In recent years, with the growing demand for higher capacity, longer cycling life, and higher power and energy density of lithium ion batteries (LIBs), the traditional insertion‐based anodes are increasingly considered out of their depth. Herein, attention is paid to the structural reorganization electrode, which is the general term for conversion‐based and alloying‐based materials according to their common characteristics during the lithiation/delithiation process. This Review summarizes the recent achievements in improving and understanding the lithium storage performance of conversion‐based anodes (especially the most widely studied transition metal oxides like Mn‐, Fe‐, Co‐, Ni‐, and Cu‐based oxides) and alloying‐based anodes (mainly including Si‐, Sn‐, Ge‐, and Sb‐based materials). The synthesis schemes, morphological control and reaction mechanism of these materials are also included. Finally, viewpoints about the challenges and feasible improvement measures for future development in this direction are given. The aim of this Review is to shed some light on future electrode design trends of structural reorganization anode materials for LIBs.     

An Overview and Future Perspectives of Rechargeable Zinc Batteries

Aqueous rechargeable zinc‐based batteries have sparked a lot of enthusiasm in the energy storage field recently due to their inherent safety, low cost, and environmental friendliness. Although remarkable progress has been made in the exploration of performance so far, there are still many challenges such as low working voltage and dissolution of electrode materials at the material and system level. Herein, the central tenet is to establish a systematic summary for the construction and mechanism of different aqueous zinc‐based batteries. Details for three major zinc‐based battery systems, including alkaline rechargeable Zn‐based batteries (ARZBs), aqueous Zn ion batteries (AZIBs), and dual‐ion hybrid Zn batteries (DHZBs) are given. First, the electrode materials and energy storage mechanism of the three types of zinc‐based batteries are discussed to provide universal guidance for these batteries. Then, the electrode behavior of zinc anodes and strategies to deal with problems such as dendrite and passivation are recommended. Finally, some challenge‐oriented solutions are provided to facilitate the next development of zinc‐based batteries. Combining the characteristics of zinc‐based batteries with good use of concepts and ideas from other disciplines will surely pave the way for its commercialization.     

Recent Advances in Layered Ti3C2Tx MXene for Electrochemical Energy Storage

Ti₃C₂T_x, a typical representative among the emerging family of 2D layered transition metal carbides and/or nitrides referred to as MXenes, has exhibited multiple advantages including metallic conductivity, a plastic layer structure, small band gaps, and the hydrophilic nature of its functionalized surface. As a result, this 2D material is intensively investigated for application in the energy storage field. The composition, morphology and texture, surface chemistry, and structural configuration of Ti₃C₂T_x directly influence its electrochemical performance, e.g., the use of a well‐designed 2D Ti₃C₂T_x as a rechargeable battery anode has significantly enhanced battery performance by providing more chemically active interfaces, shortened ion‐diffusion lengths, and improved in‐plane carrier/charge‐transport kinetics. Some recent progresses of Ti₃C₂T_x MXene are achieved in energy storage. This Review summarizes recent advances in the synthesis and electrochemical energy storage applications of Ti₃C₂T_x MXene including supercapacitors, lithium‐ion batteries, sodium‐ion batteries, and lithium–sulfur batteries. The current opportunities and future challenges of Ti₃C₂T_x MXene are addressed for energy‐storage devices. This Review seeks to provide a rational and in‐depth understanding of the relation between the electrochemical performance and the nanostructural/chemical composition of Ti₃C₂T_x, which will promote the further development of 2D MXenes in energy‐storage applications.     

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.     

Rechargeable Seawater Batteries—From Concept to Applications

Harvesting energy from natural resources is of significant interest because of their abundance and sustainability. Seawater is the most abundant natural resource on earth, covering two‐thirds of the surface. The rechargeable seawater battery is a new energy storage platform that enables interconversion of electrical energy and chemical energy by tapping into seawater as an infinite medium. Here, an overview of the research and development activities of seawater batteries toward practical applications is presented. Seawater batteries consist of anode and cathode compartments that are separated by a Na‐ion conducting membrane, which allows only Na⁺ ion transport between the two electrodes. The roles and drawbacks of the three key components, as well as the development concept and operation principles of the batteries on the basis of previous reports are covered. Moreover, the prototype manufacturing lines for mass production and automation, and potential applications, particularly in marine environments are introduced. Highlighting the importance of engineering the cell components, as well as optimizing the system level for a particular application and thereby successful market entry, the key issues to be resolved are discussed, so that the seawater battery can emerge as a promising alternative to existing rechargeable batteries.     

Dual‐Layered Film Protected Lithium Metal Anode to Enable Dendrite‐Free Lithium Deposition

Lithium metal batteries (such as lithium–sulfur, lithium–air, solid state batteries with lithium metal anode) are highly considered as promising candidates for next‐generation energy storage systems. However, the unstable interfaces between lithium anode and electrolyte definitely induce the undesired and uncontrollable growth of lithium dendrites, which results in the short‐circuit and thermal runaway of the rechargeable batteries. Herein, a dual‐layered film is built on a Li metal anode by the immersion of lithium plates into the fluoroethylene carbonate solvent. The ionic conductive film exhibits a compact dual‐layered feature with organic components (ROCO₂Li and ROLi) on the top and abundant inorganic components (Li₂CO₃ and LiF) in the bottom. The dual‐layered interface can protect the Li metal anode from the corrosion of electrolytes and regulate the uniform deposition of Li to achieve a dendrite‐free Li metal anode. This work demonstrates the concept of rational construction of dual‐layered structured interfaces for safe rechargeable batteries through facile surface modification of Li metal anodes. This not only is critically helpful to comprehensively understand the functional mechanism of fluoroethylene carbonate but also affords a facile and efficient method to protect Li metal anodes.     

Interlayer‐Spacing‐Regulated VOPO4 Nanosheets with Fast Kinetics for High‐Capacity and Durable Rechargeable Magnesium Batteries

Owing to the low‐cost, safety, dendrite‐free formation, and two‐electron redox properties of magnesium (Mg), rechargeable Mg batteries are considered as promising next‐generation secondary batteries with high specific capacity and energy density. However, the clumsy Mg²⁺ with high polarity inclines to sluggish Mg insertion/deinsertion, leading to inadequate reversible capacity and rate performance. Herein, 2D VOPO₄ nanosheets with expanded interlayer spacing (1.42 nm) are prepared and applied in rechargeable magnesium batteries for the first time. The interlayer expansion provides enough diffusion space for fast kinetics of MgCl⁺ ion flux with low polarization. Benefiting from the structural configuration, the Mg battery exhibits a remarkable reversible capacity of 310 mAh g^?1 at 50 mA g^?1, excellent rate capability, and good cycling stability (192 mAh g^?1 at 100 mA g^?1 even after 500 cycles). In addition, density functional theory (DFT) computations are conducted to understand the electrode behavior with decreased MgCl⁺ migration energy barrier compared with Mg²⁺. This approach, based on the regulation of interlayer distance to control cation insertion, represents a promising guideline for electrode material design on the development of advanced secondary multivalent‐ion batteries.     

Understanding Fundamentals and Reaction Mechanisms of Electrode Materials for Na‐Ion Batteries

Development of efficient, affordable, and sustainable energy storage technologies has become an area of interest due to the worsening environmental issues and rising technological dependence on Li‐ion batteries. Na‐ion batteries (NIBs) have been receiving intensive research efforts during the last few years. Owing to their potentially low cost and relatively high energy density, NIBs are promising energy storage devices, especially for stationary applications. A fundamental understanding of electrode properties during electrochemical reactions is important for the development of low cost, high‐energy density, and long shelf life NIBs. This Review aims to summarize and discuss reaction mechanisms of the major types of NIB electrode materials reported. By appreciating how the material works and the fundamental flaws it possesses, it is hoped that this Review will assist readers in coming up with innovative solutions for designing better materials for NIBs.     

Paving the Path toward Reliable Cathode Materials for Aluminum‐Ion Batteries

Aluminum metal is a high‐energy‐density carrier with low cost, and thus endows rechargeable aluminum batteries (RABs) with the potential to act as an inexpensive and efficient electrochemical device, so as to supplement the increasing demand for energy storage and conversion. Despite the enticing aspects regarding cost and energy density, the poor reversibility of electrodes has limited the pursuit of RABs for a long time. Fortunately, ionic‐liquid electrolytes enable reversible aluminum plating/stripping at room temperature, and they lay the very foundation of RABs. In order to integrate with the aluminum‐metal anode, the selection of the cathode is pivotal, but is limited at present. The scant option of a reliable cathode can be accounted for by the intrinsic high charge density of Al³⁺ ions, which results in sluggish diffusion. Hence, reliable cathode materials are a key challenge of burgeoning RABs. Herein, the main focus is on the insertion cathodes for RABs also termed aluminum‐ion batteries, and the recent progress and optimization methods are summarized. Finally, an outlook is presented to navigate the possible future work.     

Advanced Materials for Energy Storage

Popularization of portable electronics and electric vehicles worldwide stimulates the development of energy storage devices, such as batteries and supercapacitors, toward higher power density and energy density, which significantly depends upon the advancement of new materials used in these devices. Moreover, energy storage materials play a key role in efficient, clean, and versatile use of energy, and are crucial for the exploitation of renewable energy. Therefore, energy storage materials cover a wide range of materials and have been receiving intensive attention from research and development to industrialization. In this Review, firstly a general introduction is given to several typical energy storage systems, including thermal, mechanical, electromagnetic, hydrogen, and electrochemical energy storage. Then the current status of high‐performance hydrogen storage materials for on‐board applications and electrochemical energy storage materials for lithium‐ion batteries and supercapacitors is introduced in detail. The strategies for developing these advanced energy storage materials, including nanostructuring, nano‐/microcombination, hybridization, pore‐structure control, configuration design, surface modification, and composition optimization, are discussed. Finally, the future trends and prospects in the development of advanced energy storage materials are highlighted.     

锂离子电池正负极材料的研究

锂离子电池作为新一代的充电电池,近年来得到了飞速的发展.它以高的性能被用于手机电池、笔记本电脑和其它便携式电器.不久的将来,它将会为电动汽车或大型储存电能的电池提供能量.本文阐述了锂离子电池技术发展的现状,其中包括正极材料、负极材料、电解质以及与之发展相关的问题的成因,并分析了它们的优缺点.     

Fading Mechanisms and Voltage Hysteresis in FeF2–NiF2 Solid Solution Cathodes for Lithium and Lithium‐Ion Batteries

The rapid development of ultrahigh‐capacity alloying or conversion‐type anodes in rechargeable lithium (Li)‐ion batteries calls for matching cathodes for next‐generation energy storage devices. The high volumetric and gravimetric capacities, low cost, and abundance of iron (Fe) make conversion‐type iron fluoride (FeF₂ and FeF₃)‐based cathodes extremely promising candidates for high specific energy cells. Here, the substantial boost in the capacity of FeF₂ achieved with the addition of NiF₂ is reported. A systematic study of a series of FeF₂–NiF₂ solid solution cathodes with precisely controlled morphology and composition reveals that the presence of Ni may undesirably accelerate capacity fading. Using a powerful combination of state‐of‐the‐art analytical techniques in combination with the density functional theory calculations, fundamental mechanisms responsible for such a behavior are uncovered. The unique insights reported in this study highlight the importance of careful selection of metals and electrolytes for optimizing electrochemical properties of metal fluoride cathodes.     

Design Principles of Functional Polymer Separators for High‐Energy,Metal‐Based Batteries

Next‐generation rechargeable batteries that offer high energy density, efficiency, and reversibility rely on cell configurations that enable synergistic operations of individual components. They must also address multiple emerging challenges,which include electrochemical stability, transport efficiency, safety, and active material loss. The perspective of this Review is that rational design of the polymeric separator, which is used widely in rechargeable batteries, provides a rich set of opportunities for new innovations that should enable batteries to meet many of these needs. This perspective is different from the conventional view of the polymer separator as an inert/passive unit in a battery, which has the sole function to prevent direct contact between electrically conductivecomponents that form the battery anode and cathode. Polymer separators, which serve as the core component in a battery, bridge the electrodes and the electrolyte with a large surface contact that can be utilized to apply desirable functions. This Review focuses specifically on recent advances in polymer separator systems, with a detailed analysis of several embedded functional agents that are incorporated to improve mechanical robustness, regulate ion and mass transport, and retard flammability. The discussion is also extended to new composite separator concepts that are designated traditionally as polymer/gel electrolytes.     

Metal–Organic Framework‐Derived Materials for Sodium Energy Storage

Recently, sodium‐ion batteries (SIBs) are extensively explored and are regarded as one of the most promising alternatives to lithium‐ion batteries for electrochemical energy conversion and storage, owing to the abundant raw material resources, low cost, and similar electrochemical behavior of elemental sodium compared to lithium. Metal–organic frameworks (MOFs) have attracted enormous attention due to their high surface areas, tunable structures, and diverse applications in drug delivery, gas storage, and catalysis. Recently, there has been an escalating interest in exploiting MOF‐derived materials as anodes for sodium energy storage due to their fast mass transport resulting from their highly porous structures and relatively simple preparation methods originating from in situ thermal treatment processes. In this Review, the recent progress of the sodium‐ion storage performances of MOF‐derived materials, including MOF‐derived porous carbons, metal oxides, metal oxide/carbon nanocomposites, and other materials (e.g., metal phosphides, metal sulfides, and metal selenides), as SIB anodes is systematically and completely presented and discussed. Moreover, the current challenges and perspectives of MOF‐derived materials in electrochemical energy storage are discussed.     

Ti‐Based Oxide Anode Materials for Advanced Electrochemical Energy Storage: Lithium/Sodium Ion Batteries and Hybrid Pseudocapacitors

Titanium‐based oxides including TiO₂ and M‐Ti‐O compounds (M = Li, Nb, Na, etc.) family, exhibit advantageous structural dynamics (2D ion diffusion path, open and stable structure for ion accommodations) for practical applications in energy storage systems, such as lithium‐ion batteries, sodium‐ion batteries, and hybrid pseudocapacitors. Further, Ti‐based oxides show high operating voltage relative to the deposition of alkali metal, ensuring full safety by avoiding the formation of lithium and sodium dendrites. On the other hand, high working potential prevents the decomposition of electrolyte, delivering excellent rate capability through the unique pseudocapacitive kinetics. Nevertheless, the intrinsic poor electrical conductivity and reaction dynamics limit further applications in energy storage devices. Recently, various work and in‐depth understanding on the morphologies control, surface engineering, bulk‐phase doping of Ti‐based oxides, have been promoted to overcome these issues. Inspired by that, in this review, the authors summarize the fundamental issues, challenges and advances of Ti‐based oxides in the applications of advanced electrochemical energy storage. Particularly, the authors focus on the progresses on the working mechanism and device applications from lithium‐ion batteries to sodium‐ion batteries, and then the hybrid pseudocapacitors. In addition, future perspectives for fundamental research and practical applications are discussed.     

Nanocomposite Materials for the Sodium–Ion Battery: A Review

Clean energy has become an important topic in recent decades because of the serious global issues related to the development of energy, such as environmental contamination, and the intermittence of the traditional energy sources. Creating new battery‐related energy storage facilities is an urgent subject for human beings to address and for solutions for the future. Compared with lithium‐based batteries, sodium–ion batteries have become the new focal point in the competition for clean energy solutions and have more potential for commercialization due to the huge natural abundance of sodium. Nevertheless, sodium–ion batteries still exhibit some challenges, like inferior electrochemical performance caused by the bigger ionic size of Na⁺ ions, the detrimental volume expansion, and the low conductivity of the active materials. To solve these issues, nanocomposites have recently been applied as a new class of electrodes to enhance the electrochemical performance in sodium batteries based on advantages that include the size effect, high stability, and excellent conductivity. In this Review, the recent development of nanocomposite materials applied in sodium–ion batteries is summarized, and the existing challenges and the potential solutions are presented.