高电压钴酸锂正极材料研究进展

Research Progress of High Voltage Lithium Cobalt Oxide Cathode Materials

钴酸锂(LiCoO_(2))因具有较高比容量、高放电平台及压实密度等优点,是目前用于3C等消费类电池的主要正极活性材料。随着电子产品的轻量化、微型化发展,人们对钴酸锂体系锂离子电池能量密度和循环性能的要求逐渐提高,如何有效提升能量密度是当前亟需解决的问题。提升能量密度的方法主要有开发高比容量活性材料、提升材料的压实密度和提高工作电压。其中,提高工作电压是现阶段最有效的方式。在高充电截止电压(>4.4 V)下,钴酸锂脱锂量增加,更多活性Li+参与脱嵌过程,使得材料的实际克容量得到显著提升。同时,高工作电压会造成材料的结构发生不可逆相转变、界面副反应增多等问题,导致材料性能降低,电池容量衰减。针对这些问题,近些年研究者对高电压钴酸锂做了大量改性研究,解决方法主要集中在体相掺杂和表面包覆。体相掺杂能提高材料的结构稳定性,延缓层状结构坍塌。表面包覆对缓解界面副反应有显著的作用。通过改性来实现相转变及界面副反应的有效控制对推动高电压钴酸锂的商业化发展具有重要意义。本文主要以高电压钴酸锂材料作为切入点,总结了钴酸锂的结构组成、制备方法以及高工作电压下性能衰减原因,重点讨论了高电压钴酸锂的体相掺杂和包覆改性的研究进展,深入分析了改性对材料结构及电化学性能的影响,最后对高电压钴酸锂正极材料的发展趋势进行展望。

Because of its high specific capacity,discharge platform,and compaction density,lithium cobalt oxide(LiCoO_(2))is still the dominant cathode material for lithium-ion batteries in portable electronics such as 3C.With the development of lightweight and miniaturization of portable electronics,the requirements for high energy density and long-cycle performance of lithium-ion batteries with lithium cobalt oxide system have increased.Effective enhancement of energy density is an urgent problem requiring a solution.The methods to improve energy density include developing new active materials with high specific capacity,increasing the compaction density,and increasing the working voltage of materials.Amongst these methods,the most effective approach is to increase the working voltage.At the upper charge cut-off voltage(>4.4 V),the amount of lithium removed fromlithium cobalt oxide increases and more active Li+participates in the de-intercalation process,which significantly improves the actual gram capacity.However,several detrimental issues including irreversible phase transitions and interfacial side reactions emerge,which result in the degradation of material performance and the rapid loss of capacity.To solve these problems,researchers have modified high-voltage lithium cobalt oxide in recent years.These modifications primarily focus on bulk doping and surface coating.Bulk doping improves the structural stability of the material and delays the collapse of layered structures.Surface coating plays a significant role in alleviating the interfacial side reactions.The effective control of phase transitions and interfacial side reactions by modification is of great significance to promote the commercial development of high-voltage lithium cobalt oxide.This review focuses on the high-voltage lithium cobalt oxide material.Its structure,preparation method,and performance degradation at high working voltage are summarized.Additionally,recent developments in bulk doping and coating modification of high-voltage lithium cobalt oxide are introduced in detail and the effects of modification on the structure and electrochemical performance of the material are deeply analyzed.Finally,the development of high-voltage lithium cobalt oxide cathode materials is also discussed.