25th Anniversary Article: Understanding the Lithiation of Silicon and Other Alloying Anodes for Lithium‐Ion Batteries

Alloying anodes such as silicon are promising electrode materials for next‐generation high energy density lithium‐ion batteries because of their ability to reversibly incorporate a high concentration of Li atoms. However, alloying anodes usually exhibit a short cycle life due to the extreme volumetric and structural changes that occur during lithium insertion/extraction; these transformations cause mechanical fracture and exacerbate side reactions. To solve these problems, there has recently been significant attention devoted to creating silicon nanostructures that can accommodate the lithiation‐induced strain and thus exhibit high Coulombic efficiency and long cycle life. In parallel, many experiments and simulations have been conducted in an effort to understand the details of volumetric expansion, fracture, mechanical stress evolution, and structural changes in silicon nanostructures. The fundamental materials knowledge gained from these studies has provided guidance for designing optimized Si electrode structures and has also shed light on the factors that control large‐volume change solid‐state reactions. In this paper, we review various fundamental studies that have been conducted to understand structural and volumetric changes, stress evolution, mechanical properties, and fracture behavior of nanostructured Si anodes for lithium‐ion batteries and compare the reaction process of Si to other novel anode materials.     

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.     

Nanostructured Silicon Anodes for Lithium Ion Rechargeable Batteries

Rechargeable lithium ion batteries are integral to today's information‐rich, mobile society. Currently they are one of the most popular types of battery used in portable electronics because of their high energy density and flexible design. Despite their increasing use at the present time, there is great continued commercial interest in developing new and improved electrode materials for lithium ion batteries that would lead to dramatically higher energy capacity and longer cycle life. Silicon is one of the most promising anode materials because it has the highest known theoretical charge capacity and is the second most abundant element on earth. However, silicon anodes have limited applications because of the huge volume change associated with the insertion and extraction of lithium. This causes cracking and pulverization of the anode, which leads to a loss of electrical contact and eventual fading of capacity. Nanostructured silicon anodes, as compared to the previously tested silicon film anodes, can help overcome the above issues. As arrays of silicon nanowires or nanorods, which help accommodate the volume changes, or as nanoscale compliant layers, which increase the stress resilience of silicon films, nanoengineered silicon anodes show potential to enable a new generation of lithium ion batteries with significantly higher reversible charge capacity and longer cycle life.     

The State and Challenges of Anode Materials Based on Conversion Reactions for Sodium Storage

Sodium‐ion batteries (SIBs) have huge potential for applications in large‐scale energy storage systems due to their low cost and abundant sources. It is essential to develop new electrode materials for SIBs with high performance in terms of energy density, cycle life, and cost. Metal binary compounds that operate through conversion reactions hold promise as advanced anode materials for sodium storage. This Review highlights the storage mechanisms and advantages of conversion‐type anode materials and summarizes their recent development. Although conversion‐type anode materials have high theoretical capacities and abundant varieties, they suffer from multiple challenging obstacles to realize commercial applications, such as low reversible capacity, large voltage hysteresis, low initial coulombic efficiency, large volume changes, and low cycling stability. These key challenges are analyzed in this Review, together with emerging strategies to overcome them, including nanostructure and surface engineering, electrolyte optimization, and battery configuration designs. This Review provides pertinent insights into the prospects and challenges for conversion‐type anode materials, and will inspire their further study.     

Silicon‐Based Anodes for Lithium‐Ion Batteries: From Fundamentals to Practical Applications

Silicon has been intensively studied as an anode material for lithium‐ion batteries (LIB) because of its exceptionally high specific capacity. However, silicon‐based anode materials usually suffer from large volume change during the charge and discharge process, leading to subsequent pulverization of silicon, loss of electric contact, and continuous side reactions. These transformations cause poor cycle life and hinder the wide commercialization of silicon for LIBs. The lithiation and delithiation behaviors, and the interphase reaction mechanisms, are progressively studied and understood. Various nanostructured silicon anodes are reported to exhibit both superior specific capacity and cycle life compared to commercial carbon‐based anodes. However, some practical issues with nanostructured silicon cannot be ignored, and must be addressed if it is to be widely used in commercial LIBs. This Review outlines major impactful work on silicon‐based anodes, and the most recent research directions in this field, specifically, the engineering of silicon architectures, the construction of silicon‐based composites, and other performance‐enhancement studies including electrolytes and binders. The burgeoning research efforts in the development of practical silicon electrodes, and full‐cell silicon‐based LIBs are specially stressed, which are key to the successful commercialization of silicon anodes, and large‐scale deployment of next‐generation high energy density LIBs.     

锂离子电池硅基负极用粘结剂的设计改性进展

发展锂离子电池是缓解当前能源和环境问题的有力措施,但其能量密度已无法满足未来储能装置的高要求。发展高比能量型锂离子电池必须从提高电极材料的性能入手。硅基材料具有容量高、成本低、平台电压低等优点,被认为是最具潜力的负极材料。然而,该类材料在充放电过程中会发生巨大的体积变化(300%),导致电池容量下降严重甚至失效。近年来,研究者们开始着眼于通过对电极中的粘结剂进行结构设计和复合改性来提升硅基负极的性能,并取得了显著的效果。基于硅基负极目前存在的问题,总结了适用于硅基负极的粘结剂类型,并从粘结剂分子链结构设计和增强电极微粒间作用力这两个方面综述了近年来硅基负极中粘结剂的设计改性进展,最终展望了硅基负极用粘结剂的发展趋势和未来前景。      

Dendrimer Based Binders Enable Stable Operation of Silicon Microparticle Anodes in Lithium-Ion Batteries

High-capacity anode materials (e.g., Si) are highly needed for high energy density battery systems, but they usually suffer from low initial coulombic efficiency (CE), short cycle life, and low-rate capability caused by large volume changes during the charge and discharge process. Here, a novel dendrimer-based binder for boosting the electrochemical performance of Si anodes is developed. The polyamidoamine (PMM) dendrimer not only can be used as binder, but also can be utilized as a crosslinker to construct 3D polyacrylic acid (PAA)-PMM composite binder for high-performance Si microparticles anodes. Benefiting from maximum interface interaction, strong average peeling force, and high elastic recovery rate of PAA-PMM composite, the Si electrode based on PAA-PMM achieves a high specific capacity of 3590 mAh g⁻¹ with an initial CE of 91.12%, long-term cycle stability with 69.80% retention over 200 cycles, and outstanding rate capability (1534.8 mAh g⁻¹ at 3000 mA g⁻¹). This work opens a new avenue to use dendrimer chemistry for the development of high-performance binders for high-capacity anode materials.     

Efficient Sodium Storage in Rolled‐Up Amorphous Si Nanomembranes

Alloying‐type materials are promising anodes for high‐performance sodium‐ion batteries (SIBs) because of their high capacities and low Na‐ion insertion potentials. However, the typical candidates, such as P, Sn, Sb, and Pb, suffer from severe volume changes (≈293–487%) during the electrochemical reactions, leading to inferior cycling performances. Here, a high‐rate and ultrastable alloying‐type anode based on the rolled‐up amorphous Si nanomembranes is demonstrated. The rolled‐up amorphous Si nanomembranes show a very small volume change during the sodiation/desodiation processes and deliver an excellent rate capability and ultralong cycle life up to 2000 cycles with 85% capacity retention. The structural evolution and pseudocapacitance contribution are investigated by using the ex situ characterization techniques combined with kinetics analysis. Furthermore, the mechanism of efficient sodium‐ion storage in amorphous Si is kinetically analyzed through an illustrative atomic structure with dangling bonds, offering a new perspective on understanding the sodium storage behavior. These results suggest that nanostructured amorphous Si is a promising anode material for high‐performance SIBs.     

Transition metal chalcogenide anodes for sodium storage

Owing to the low cost and indefinite availability of sodium resources, rechargeable sodium-ion batteries (SIBs) are now being considered as the most appealing alternatives to their lithium-ion counterparts for large scale applications. On the other hand, transition metal chalcogenides (TMCs) have emerged as potential candidates of SIB anodes due to their versatile material species, ample abundance, low cost, robust nature and high theoretical capacities. However, TMCs still face several challenges like severe volume changes during sodiation/desodiation, inadequate conductivities and large-scale productions. Hence, many traditional and unconventional techniques have been developed to mitigate these issues and obtain high quality electrode materials for practical applications. In this review, recent progress and the rectification stratagems of the problems of TMCs have been summarized firstly. Then, a detailed comparison of transition metal selenides with sulfide TMCs family members was provided to investigate the factors which govern the relative performance improvements of selenides. Besides this, multiple transition metals containing TMCs (M-TMCs) have exhibited intriguingly better performances compared to mono-metal TMCs. Hence, various inspirational features of M-TMCs were discussed. As an outcome of these discussions, we were able to outline several outlooks and prospective solutions for the rectification of potential challenges of TMC anode materials.     

Progress and perspectives on alloying-type anode materials for advanced potassium-ion batteries

Potassium-ion batteries (PIBs) have attracted increasing interest as promising alternatives to lithium-ion batteries (LIBs) for application in large-scale electrical energy storage systems (EESSs) owing to a wide earth-abundance, potential price advantages, and low standard redox potential of potassium. Developmental materials for use in PIBs that can yield high specific capacities and durability are widely sought with emerging studies on alloying-type anode materials offering significant prospects to meet this challenge. Here, recent advances on alloying-type anodes and their composites for PIBs are reviewed in detail and in a systematic way to capture key aspects from fundamental working principles through major progress and achievements to future perspectives and challenges. Emphasis is placed on critical aspects such as the alloying mechanism and correlation of electrode design and structural engineering for performance enhancement and the crucial role of electrolyte compatibility, additives and binders. The review in appraising all the important contributions on this topic allows for a critical assessment of the research challenges and provides insights on future research directions that can accelerate the important development of PIBs as a viable battery energy storage system.     

Focus on Spinel Li4Ti5O12 as Insertion Type Anode for High‐Performance Na‐Ion Batteries

Sodium‐ion batteries (SIBs) toward large‐scale energy storage applications has fascinated researchers in recent years owing to the low cost, environmental friendliness, and inestimable abundance. The similar chemical and electrochemical properties of sodium and lithium make sodium an easy substitute for lithium in lithium‐ion batteries. However, the main issues of limited cycle life, low energy density, and poor power density hamper the commercialization process. In the last few years, the development of electrode materials for SIBs has been dedicated to improving sodium storage capacities, high energy density, and long cycle life. The insertion type spinel Li₄Ti₅O₁₂ (LTO) possesses “zero‐strain” behavior that offers the best cycle life performance among all reported oxide‐based anodes, displaying a capacity of 155 mAh g^?1 via a three‐phase separation mechanism, and competing for future topmost high energy anode for SIBs. Recent reports offer improvement of overall electrode performance through carbon coating, doping, composites with metal oxides, and surface modification techniques, etc. Further, LTO anode with its structure and properties for SIBs is described and effective methods to improve the LTO performance are discussed in both half‐cell and practical configuration, i.e., full‐cell, along with future perspectives and solutions to promote its use.     

金属惰性阳极的研究进展

综述了近年来国内外铝电解用铜基合金、铜镍基合金和镍基合金惰性阳极方面所做的研究工作,分析了各种惰性阳极的优缺点和可行的研究方向。围绕提高材料的抗氧化和耐腐蚀性,提出了两方面的建议：一方面通过调节材料成分,使其表面氧化膜的生成与溶解达到动态平衡;另一方面开发新的电解质体系,获得“低初晶温度、高Al2O3溶解度”的电解质,降低阳极腐蚀率。     

Recent research progress of alloy-containing lithium anodes in lithium-metal batteries

Lithium metal is regarded as one of the most ideal anode materials for next-generation batteries, due to its high theoretical capacity of 3860 mAh g⁻¹ and low redox potential (−3.04 V vs standard hydrogen electrode). However, practical applications of lithium anodes are impeded by the uncontrollable growth of lithium dendrite and continuous reactions between lithium and electrolyte during cycling processes. According to reports for decades, artificial solid electrolyte interface (SEI), electrolyte additives, and construction of three-dimensional (3D) structures are demonstrated essential strategies. Among numerous approaches, metals that can alloy with lithium have been employed to homogenize lithium deposition and accelerate Li ion transportation, which attract more and more attention. This review aims to summarize the lithium alloying applied in lithium anodes including the fabricating approaches of alloy-containing lithium anodes, and the action mechanism and challenges of fabricated lithium anodes. Based on summarizing the literature, shortcomings and challenges as well as the prospects are also analyzed, to impel further research of lithium anodes and lithium-based batteries.     

Multi-electron reaction materials for sodium-based batteries

Sodium-based rechargeable batteries are very promising energy storage and conversion systems owing to their wide availability and the low cost of Na resources, which is beneficial to large-scale electric energy storage applications in future. In the context of attempting to achieve high-energy densities and low cost, multi-electron reaction materials for both cathodes and anodes are attracting significant attention due to high specific capacities involved. Here, we present a brief review on recently reported multi-electron reaction materials for sodium-based batteries. We mostly concentrate on true multi-electron reactions that involve individually valence changes greater than one per redox center, but in addition include materials in the discussion, which undergo multi-electron processes per formula unit. The theoretical gravimetric and volumetric (expanded state) capacities are studied for a broad range of examples. Then, the practically achievable volumetric energy density and specific energy of Na cells with hard carbon, sodium (Na), and phosphorus (P) anodes are compared. For this purpose, various data are recalculated and referred to the same basis cell. The results show the potential superiority of the cells using multi-electron reaction materials and provide an intuitive understanding of the practically achievable energy densities in future Na-based rechargeable batteries. However, these multi-electron reaction materials are facing several key challenges, which are preventing their high-performance in current cells. In order to overcome them, general strategies from particle design to electrolyte modification are reviewed and several examples in both cathode and anode materials using such strategies are studied. Finally, future trends and perspectives for achieving promising Na-based batteries with better performance are discussed.     

Structural changes in ScCeSZ–NiO ceramics in a high-temperature hydrogen environment

It is shown that, in a solid oxide cell with ceramic Ni-containing anodes, in the first working cycle, the anode material is reduced in hydrogen, which causes changes in its microstructure and properties. We analyze structural changes in the anode material with different contents of NiO from the nonreduced (ScCeSZ–NiO) to the reduced (ScCeSZ–Ni) state, which are connected with its electric conductance.     

Design Strategies to Enable the Efficient Use of Sodium Metal Anodes in High-Energy Batteries

Sodium-based batteries have attracted considerable attention and are recognized as ideal candidates for large-scale and low-cost energy storage. Sodium (Na) metal anodes are considered as one of the most promising anodes for next-generation, high-energy, Na-based batteries owing to their high theoretical specific capacity (1166 mA h g⁻¹) and low standard electrode potential. Herein, an overview of the recent developments in Na metal anodes for high-energy batteries is provided. The high reactivity and large volume expansion of Na metal anodes during charge and discharge make the electrode/electrolyte interphase unstable, leading to the formation of Na dendrites, short cycle life, and safety issues. Design strategies to enable the efficient use of Na metal anodes are elucidated, including liquid electrolyte engineering, electrode/electrolyte interface optimization, sophisticated electrode construction, and solid electrolyte engineering. Finally, the remaining challenges and future research directions are identified. It is hoped that this progress report will shape a consistent view of this field and provide inspiration for future research to improve Na metal anodes and enable the development of high-energy sodium batteries.     

Nanoscale Engineering of Heterostructured Anode Materials for Boosting Lithium‐Ion Storage

Rechargeable lithium‐ion batteries (LIBs), as one of the most important electrochemical energy‐storage devices, currently provide the dominant power source for a range of devices, including portable electronic devices and electric vehicles, due to their high energy and power densities. The interest in exploring new electrode materials for LIBs has been drastically increasing due to the surging demands for clean energy. However, the challenging issues essential to the development of electrode materials are their low lithium capacity, poor rate ability, and low cycling stability, which strongly limit their practical applications. Recent remarkable advances in material science and nanotechnology enable rational design of heterostructured nanomaterials with optimized composition and fine nanostructure, providing new opportunities for enhancing electrochemical performance. Here, the progress as to how to design new types of heterostructured anode materials for enhancing LIBs is reviewed, in the terms of capacity, rate ability, and cycling stability: i) carbon‐nanomaterials‐supported heterostructured anode materials; ii) conducting‐polymer‐coated electrode materials; iii) inorganic transition‐metal compounds with core@shell structures; and iv) combined strategies to novel heterostructures. By applying different strategies, nanoscale heterostructured anode materials with reduced size, large surfaces area, enhanced electronic conductivity, structural stability, and fast electron and ion transport, are explored for boosting LIBs in terms of high capacity, long cycling lifespan, and high rate durability. Finally, the challenges and perspectives of future materials design for high‐performance LIB anodes are considered. The strategies discussed here not only provide promising electrode materials for energy storage, but also offer opportunities in being extended for making a variety of novel heterostructured nanomaterials for practical renewable energy applications.     

Carbon‐Based Alloy‐Type Composite Anode Materials toward Sodium‐Ion Batteries

In the scenario of renewable clean energy gradually replacing fossil energy, grid‐scale energy storage systems are urgently necessary, where Na‐ion batteries (SIBs) could supply crucial support, due to abundant Na raw materials and a similar electrochemical mechanism to Li‐ion batteries. The limited energy density is one of the major challenges hindering the commercialization of SIBs. Alloy‐type anodes with high theoretical capacities provide good opportunities to address this issue. However, these anodes suffer from the large volume expansion and inferior conductivity, which induce rapid capacity fading, poor rate properties, and safety issues. Carbon‐based alloy‐type composites (CAC) have been extensively applied in the effective construction of anodes that improved electrochemical performance, as the carbon component could alleviate the volume change and increase the conductivity. Here, state‐of‐the‐art CAC anode materials applied in SIBs are summarized, including their design principle, characterization, and electrochemical performance. The corresponding alloying mechanism along with its advantages and disadvantages is briefly presented. The crucial roles and working mechanism of the carbon matrix in CAC anodes are discussed in depth. Lastly, the existing challenges and the perspectives are proposed. Such an understanding critically paves the way for tailoring and designing suitable alloy‐type anodes toward practical applications.     

Progress in Ni-based anode materials for direct hydrocarbon solid oxide fuel cells

Ni-based anode materials of solid oxide fuel cells (SOFCs) are susceptible to carbon deposition and deactivation in direct hydrocarbon fuels, greatly limiting the commercialization. Extensive studies on finding new alternative anode materials have been developed; however, new problems such as low electrochemical performance and complex cell preparation process destroyed the further research passion of Ni-free anode materials. Considering the superior catalytic activity and mature technology of Ni-based anode materials, a large number of recent research results proved that it is still important and promising to solve the carbon coking of Ni-based anode materials. In this review, progress in four typically promising Ni-based anode materials free from carbon coking has been summarized, including the noble metals, ceria, Ba-containing oxides and titanium oxide. Correspondingly, the mechanisms that improve the carbon tolerance of Ni-based modified SOFCs anodes are clearly concluded, providing the materials and theoretical basis for the use of direct hydrocarbon SOFCs as early as possible.     

MXene-Based Dendrite-Free Potassium Metal Batteries

Potassium metal batteries are considered as attractive alternatives beyond lithium-ion batteries. However, uncontrollable dendrite growth on the potassium metal anode has restrained their practical applications. A high-performance potassium anode achieved by confining potassium metal into a titanium-deficient nitrogen-containing MXene/carbon nanotube freestanding scaffold is reported. The high electronic transport and fast potassium diffusion in this scaffold enable reduced local current density and homogeneous ionic flux during plating/stripping processes. Furthermore, as verified by theoretical calculations and experimental investigations, such “potassium-philic” MXene sheets can induce the nucleation of potassium, and guide potassium to uniformly distribute in the scaffold upon cycling. Consequently, the as-developed potassium metal anodes exhibit a dendrite-free morphology with high Coulombic efficiency and long cycle life during plating/stripping processes. Such anodes also deliver significantly improved electrochemical performances in potassium–sulfur batteries compared with bare potassium metal anodes. This work can provide a new avenue for developing potassium metal-based batteries.