高镍正极材料水洗过程中金属离子溶失机理及稳定表面构筑研究

The dissolution of lithium, cobalt and aluminum from Ni rich layer structured cathode materials during water washing process is one of the key issues which lead it suffers from poor storage property and poor electrochemical performance. This project aims to study the formation mechanism of the soluble metallic compound from Ni-rich cathode materials in the sintering and storing process, to analyze the dissolution mechanism of metal ions in the water washing process with the aid of quasi-in-situ XPS depth profiling technology in order that verifying the phase transition and structure evolution before and after water washing treatment. After that, NH4F is introduced as additive to induce in-situ co-precipitation of Lithium, Cobalt and Aluminum on the alkaline particle surface, removing Li-based residues deeply and highly efficient in-situ constructing stable interface simultaneously. Here, the relationship between the surface property and electrochemical performance of Ni rich cathode materials will be constructed based on study the microstructure, morphology and electrochemical performance evolution during charge and discharge process, revealing the Li-storage property enhancing mechanism of Ni rich cathode materials via multi-dimensional, multi-scale fluoride surface modification. The accomplishment of this project is expected to offer a new solution for designing Ni rich cathode materials with high storage property and upgraded electrochemical performance.

镍基层状氧化物正极材料在水洗过程中的锂、钴、铝金属元素溶失是导致其存储性能差和电化学性能差的关键核心问题之一。本项目首先研究高镍正极材料在烧结、存储过程中可溶性金属盐的形成机理，采用准原位XPS深度剖析技术探明材料水洗前后表面组分、物相和结构演变规律，解析金属离子水洗溶失机理。在此基础上，以NH4F为水洗添加剂，在碱性颗粒表面原位诱导锂、钴、铝重新沉淀，同步实现高镍正极材料表面锂残渣深度去除与稳定界面高效构筑。通过研究充放电循环过程中材料微观结构和形貌的变化规律，建立颗粒表界面性质与电化学性能之间的“构效关系”，明晰多尺度、多维度氟化物表面改性强化高镍正极材料储锂性能的作用机制，为提升高镍正极材料的存储性能和电化学性能提供指导。

为了解决镍基层状氧化物正极材料存储性能和电化学性能差等问题，本项目首先研究了高镍正极材料在烧结、存储过程中可溶性金属盐的形成机理，探明了高镍正极材料LiNi1-x-yCoxAlyO2 (x + y ≤ 0.2，简称NCA)烧结过程中晶格Al离心迁移和水洗过程中表层晶格Li+、Al3+离子溶失是导致材料水洗后性能失效的主要原因之一。在此基础上，以NH4F、LiH2PO4为水洗添加剂，实现了碱性颗粒表面原位诱导Li+、Al3+离子重新沉淀的同时在深度去除材料表面锂残渣与稳定界面高效构筑。改性的水洗方法获得的正极材料因表面原位包覆了Li3AlF6、LiF、Li3PO4、AlPO4等电化学稳定的化合物，有效提升了材料的电化学性能。项目执行期内共发表相关SCI 论文11篇；申请发明专利4件，授权2件；获省部级科学技术奖一等奖2项。