Advanced Current Collectors for Alkali Metal Anodes

High-energy-density batteries are in urgent need to solve the ever-increasing energy storage demand for portable electronic devices, electric vehicles, and renewable solar and wind energy systems. Alkali metals, typically lithium(Li), sodium(Na) and potassium(K), are considered as the promising anode materials owing to their low electrochemical potential, low density, and high theoretical gravimetric capacities. However, the problem of dendrite growth of alkali metals during their plating/stripping process will lead to low Coulombic efficiencies, a short lifespan and huge volume expansion, eventually hindering their practical commercialization. To resolve this issue, a very effective approach is engineering the anodes on structured current collectors. This review summarizes the development of the alkali metal batteries and discusses the recent advances in rational design of anode current collectors. First, the challenges and strategies of suppressing alkali-metal dendrite growth are presented. Then the special attention is paid to the novel current collector design for dendrite-free alkali metal anodes. Finally, we give conclusions and perspective on the current challenges and future research directions toward advanced anode current collectors for alkali metal batteries.     

On the Center of Continuous Maps of Dendrites

The structure and the depth of the center of a continuous map of a dendrite with a closed countable set of branch points of a finite order are studied. It is proved that the center of that map coincides with the closure of the set of periodic points. It is shown also that for an arbitrary natural number n S 2 there are the dendrite X n with a closed countable set of branch points of a finite order and the continuous map f n : X n M X n with n as the depth of the center.     

金属锂负极的成核机制与载体修饰

金属锂具有电位低、比容量高等突出优点,是极具吸引力的下一代高能量密度电池的负极材料,然而存在枝晶、死锂、副反应严重、库伦效率低、循环稳定性差等问题,限制了其实际应用。金属锂负极的成核是电化学沉积过程中的重要步骤,锂在集流体或导电载体上的均匀成核和稳定生长对于抑制枝晶死锂、提高充放电效率和循环性能具有关键作用。本文从成核机制与载体效应的角度概述了锂金属负极的研究进展,介绍了锂成核驱动力、异相成核模型、空间电荷模型等内容,分析了锂核尺寸及分布与过电位和电流密度的关系,并通过三维载体分散电流密度、异相晶核/电场诱导成核、晶格匹配等方面的研究实例讨论了载体修饰对锂负极的性能提升。     

锂金属负极人造保护膜的研究进展

金属锂因其具有极高的理论容量(3860 mAh·g^?1)、最低的电极电位(?3.04 V vs.标准氢电极)和低的密度(0.534 g·cm^?3),被认为是最具潜力的负极材料。但循环过程中不可控的枝晶生长及不稳定的固体电解质相界面膜所引起的安全隐患和电池库伦效率低等问题严重阻碍了锂金属负极的发展。通过在电极表面构建人造保护膜可以有效调控锂离子沉积行为,因此人造保护膜的构建是一种简单高效抑制锂枝晶生长的策略。本综述将从聚合物保护膜、无机保护膜、有机-无机复合保护膜和合金保护膜总结了人造保护膜的构建方法、抑制锂枝晶生长机理,为促进高比能锂金属电池的商业化应用提供借鉴参考作用。     

Recent Progress and Perspectives of Sodium Metal Anodes for Rechargeable Batteries

Sodium metal anodes have attracted significant attention due to their high specific capacity,low redox potential and abundant resources.However,the dendrites and unstable solid electrolyte interphase(SEI)of sodium anodes restrict the development of sodium metal batteries.This review includes the recent progress on the Na anode protection in sodium metal batteries.The strategies are summarized as modified three-dimensional current collectors,artificial solid electrolyte interphases,and electrolyte modifications.Conclusions and perspectives are envisaged for the further understanding and development of Na metal anodes.     

电极界面浓差极化对锂金属沉积的影响

锂金属作为下一代高能量密度电池的理想负极材料受到研究人员广泛关注。然而,锂枝晶生长引起的安全隐患和循环寿命短等问题严重影响了锂金属电池的实用化进程。本文以电化学现象和理论为依据,从浓差极化角度详细分析锂金属电沉积过程中枝晶生长、死锂形成和全电池失效机制,并对目前研究较多的多孔宿主电极中的浓差极化及枝晶抑制进行分析,提出锂金属界面浓差电池现象。本文得到的结论为研究人员更深入地探究锂金属保护策略提供了理论依据。     

Na-K liquid alloy:A review on wettability enhancement and ionic carrier selection mechanism

The intrinsic liquid interface of Na-K alloy allays concerns about dendrite growth on metal anodes that are thermodynamically within the room temperature(20-22℃).Nevertheless,it hinders the formation of a stable electrode structure due to the inferior wettability induced by considerable liquid tension.In addition,the dominant ionic carrier in the Na-K alloy is subject to multiple factors,which is not conducive to customized battery design.This review,based on recently reported frontier achievements on Na-K liquid anodes,summarizes practical strategies for promoting the wettability by hightemperature induction,capillary effect,vacuum infiltration,and solid interface protection.Furthermo re,four selection mechanisms of the dominant ionic carrier are presented:(1) ion property dominated,(2)cathode dominated,(3) separator dominated,and(4) solid electrolyte interface dominated.Notably,initial electrolytes in energy storage systems have been unable to play a decisive role in ionic selection.Utilizing a superior wettability strategy and simultaneously identifying the dominant ionic carrier can facilitate the tailored application of dendrite-free Na-K liquid anodes.     

Dependence on substrate topography of growth of nanosized dendritic structures in an electron-beam-induced deposition process

Nanometer-sized W-dendrites are fabricated on Al₂O₃ substrates with an electron-beam-induced deposition process. Dependence of growth of nanodendrite on surface topography is investigated with transmission electron microscopy. It is confirmed that the nanodendrite grows on convex surfaces but not around a hole on a substrate. These are attributed to different distribution of charges on surfaces with different topographies during electron beam irradiation when charges are produced on the surface due to emission of second electrons. The charges accumulate on convex surface and do not distribute around a hole. Therefore, the nanodendrite grows on the former and not on the latter.     

Electroless Formation of Hybrid Lithium Anodes for Fast Interfacial Ion Transport

Rechargeable batteries based on metallic anodes are of interest for fundamental and application‐focused studies of chemical and physical kinetics of liquids at solid interfaces. Approaches that allow facile creation of uniform coatings on these metals to prevent physical contact with liquid electrolytes, while enabling fast ion transport, are essential to address chemical instability of the anodes. Here, we report a simple electroless ion‐exchange chemistry for creating coatings of indium on lithium. By means of joint density functional theory and interfacial characterization experiments, we show that In coatings stabilize Li by multiple processes, including exceptionally fast surface diffusion of lithium ions and high chemical resistance to liquid electrolytes. Indium coatings also undergo reversible alloying reactions with lithium ions, facilitating design of high‐capacity hybrid In‐Li anodes that use both alloying and plating approaches for charge storage. By means of direct visualization, we further show that the coatings enable remarkably compact and uniform electrodeposition. The resultant In‐Li anodes are shown to exhibit minimal capacity fade in extended galvanostatic cycling when paired with commercial‐grade cathodes.