Abstract:

With the advantages of high specific capacity, low cost, environmental protection and no need for high-voltage electrolyte, nickel-rich oxide cathode materials have attracted much attention. Although the higher Ni content contributes to improve the specific discharge capacity, it also produces cationic mixing, surface and interface reactions and crack propagation which leads to structural instability, etc., resulting in poor cycle life, low thermal stability and poor storage performance of nickel-rich cathode materials, which hinder their commercial application. In order to give full play to the advantages of nickel-rich LIBs, nickel-rich oxide cathode materials have been carried out varieties of modifications. In the past decade, nickel rich cathode materials have experienced the development stages of ion doping, surface coating, single crystal, core-shell structure, concentration-gradient structure and so on. In this paper, the mechanism and research progress of doping, coating, single crystal and core-shell structure modification were briefly reviewed, and the edges and inherent shortcomings of these methods were analyzed. After that, this paper focused on the analysis of the concentration-gradient materials, which were divided into three parts according to their development stages: nickel-rich core with concentration gradient shell, linear concentration gradient materials and progressive concentration gradient materials. The synthesis methods, modification mechanism and electrochemical performance of them were introduced in detail. In a comprehensive view, the concentration gradient material can fundamentally solve the inherent weaknesses of nickel rich cathode materials, and it was believed that this technology would play an important role in the practical process of nickel rich cathode materials.

Key words: lithium ion battery, nickel-rich cathode material, concentration gradient, modification

摘要：

富镍氧化物正极材料因其具有高比容量、低成本、环保和无需高电压电解质的优点而备受关注。虽然Ni含量的增加有助于提高放电比容量，但也产生了阳离子混排、表界面反应和导致结构不稳定的裂纹扩展等缺点，导致富镍正极材料的循环寿命较差、热稳定性有待提升和储存性能较差，妨碍了其商业化应用。为尽可能地发挥富镍锂离子电池高容量的优势，研究人员对材料进行了多种改性，历经了离子掺杂、表面包覆、单晶材料、核壳结构、浓度梯度结构等发展阶段。本文首先对掺杂、包覆、单晶、核壳结构等几种改性手段进行了简要概述，分析了这几种方法的优势及本身固有的缺点。然后重点对浓度梯度材料进行了分析，根据其发展阶段分为富镍核加浓度梯度壳、线性浓度梯度材料、渐进式浓度梯度材料三个部分，从合成方法、改性机理及电化学性能等方面做了详细介绍。综合来看，浓度梯度材料可以从根本上解决富镍正极材料的固有缺点，相信这一技术会在富镍正极材料的实用化进程中发挥重要作用。

关键词: 锂离子电池, 富镍正极材料, 浓度梯度, 改性