多级结构小单晶高镍正极材料的构建、表界面调控及微裂纹抑制研究

In order to better solve the key issues including poor cyclic properties, the air sensibility and microcracks induced by sur-/interfacial structural distortion of the polycrystalline LiNi0.9Co0.07Al0.03O2 (NCA973), the project focuses on how to precisely regulate the multi-scale component and sur-/interfacial structure of the Ni-rich cathode material, and therefore to purposefully design a single crystal NCA973 by the controlable crystallization method, and further to construct the fast lithium ion conductor Li7La3Zr2O12 & Li2ZrO3 mixed coating layer via a facile sol-gel method. Simultaneously, the interfacial gradient Zr4+ doped is formed. The multi-scale sur-/interfacial modification aims to improve the structural stability and electrode-electrolyte surface interfacial conductivity and effectively inhibit microcrack generation. According to the in-situ/ex-situ characterizations and systematic electrochemical techniques/devices, the formation and regulation mechanism of micro-/heterostructures are detailedly elucidated on multi-scale levels. New insights into the mechanism of cracking inhibition, the study of air stability and the intrinsic Li+-storage mechanism are revealed. The essential structure-activity relationship and interaction theory between constituent, microstructure, sur-/interface properties and electrochemical Li+-storage performance are rationally established. The accomplishment of the project will be of great importance regarding to provide new understandings and fundamental guidance for the synthetic design, functional regulation and practical applications of high-performance electrode materials for lithium-ion batteries.

为更好解决多晶型高容量高镍正极LiNi0.9Co0.07Al0.03O2(NCA973)循环性能差、空气敏感及表界面结构畸变诱发晶内晶间微裂纹等关键问题，本项目拟从宏观(微米单晶)–微纳(表面包覆)–原子(晶格掺杂)多尺度组分和结构调控出发，通过控制结晶法可控制备小单晶型NCA973，采用溶胶-凝胶法原位构筑锂快离子导体Li7La3Zr2O12&Li2ZrO3混合包覆层并同步形成Zr4+界面梯度掺杂的多尺度表界面修饰来提高材料稳定性和电极-电解质表界面传导性并有效抑制微裂纹产生。基于（非）原位表征和系统电化学技术/装置，多层次阐明复合异质结构的形成及调控机理，揭示小单晶结构和表面多尺度修饰对抑制微裂纹扩展、降低空气敏感效应及强化储锂性能的协同作用机制，发展并建立材料组分/微观结构/表界面特性-储锂性能间的本质构效关系，为高性能锂离子电池电极材料设计合成、功能调控和应用开发提供新思路。

高镍层状LiNi0.6Co0.2Mn0.2（NCM622）材料凭借高能量密度、高工作电压及环境友好的优势而成为锂离子动力电池正极材料最有力的竞争者之一。然而，NCM622在高充电截止电压（≥4.5 V）工作条件下仍面临晶间/晶内微裂纹严重、循环寿命不足及热稳定性差等问题。针对这些问题，本项目提出了小单晶结构设计和杂原子掺杂协同改性策略，可控构建了Mo6+原位掺杂的亚微米级单晶型NCM622，并与常规多晶型和微米级单晶型NCM622进行了对比研究。研究发现，亚微米单晶结构设计协同Mo6+原位掺杂可达到以下效果：有效抵抗晶格应力应变，消除局部应力累积以避免微裂纹萌生和扩展，实现“零应变”无裂纹特性；有效减少表面有害副反应，减少表面残余物的生成，形成超薄的表面固体电解质膜，有利于表界面Li+快速传输；有效抑制材料在高脱锂态热分解过程中的晶格失氧，提升不可逆相变的转变温度，极大改善热稳定性能。最终实现了在高电压下稳定运行且机械化学性能可靠的NCM622材料。基于改性亚微米单晶结构NCM622材料组装成的袋式软包全电池展现出极其优异的高压循环稳定性、热稳定性及宽温区工作能力（−20至55 °C），其在2.8−4.5 V，1 C下，25 °C循环3000次容量保持率为80.3%。本项目提出了小单晶结构设计和杂原子掺杂协同改性策略，构建了Mo6+原位掺杂的亚微米单晶结构NCM622，揭示了小单晶结构和微结构调控对强化力学性能、热稳定性能及电化学性能的内在作用机制，为其它高性能电极材料的设计合成、功能调控和应用开发提供了新思路。