新型高容量阳离子有序/无序结构钛基富锂正极材料的研究

Developing high capacity cathode materials is an important subject in the investigation field of lithium-ion batteries. In tradition, it is considered that well-ordered crystal structure and low cation mixed are the premise of getting excellent electrochemical properties. Recent discoveries, however, point to the idea that lithium diffusion can be facile in cation-disordered rocksalt structure materials through percolating 0-TM network, which expands the design of high capacity cathodes. This project based on the dual identities of Li2TiO3, we are committed to developing a high capatity and good stability titanium-based lithium rich cathode material with cation-ordered/disordered hybrid structure. By controlling the phase distributions to achieve the target product, which primary particles consist of cation-disordered core with high capacity and cation-ordered nanosized shell with stable and fast Li+-conductor characteristic. The (de)lithiation mechanism in the cation-ordered/disordered structure materials will be investigated, specially focusing on diffusion dynamics of Li+ in the percolating 0-TM network and charge compensation mechanism by solid-state redox of oxide ions. Keys factors influencing Li+ diffusion and reversible redox of oxide ions are seeking to find out in this project. In addition, we will do research on the surface structure evolution in the charge-discharge process, and the “structure-activity” relationships of the Li+ diffusion, charge compensation and surface properties will be built. We expect that our works offer new idea and scientific basis for the development of high capacity cathode materials.

高容量正极材料的开发是锂离子电池领域的重要课题。传统认为良好有序晶体结构、阳离子混排少是获得优异电化学性能的前提。然而，近期发现的阳离子无序岩盐结构富锂正极材料可通过逾渗网络进行锂离子的快速迁移，扩展了高容量正极材料的设计思路。本项目基于Li2TiO3的双重作用，致力于发展一种高容量、良好稳定性的阳离子有序/无序混合结构钛基富锂正极材料体系。通过相分布调控使材料的一次粒子由无序相为主的高容量内核和有序相为主的既稳定表面又可快速导离子的纳米外层组成。研究锂离子在有序/无序结构材料中的脱嵌机理，特别是锂离子在逾渗网络中的扩散动力学和氧离子参与电荷补偿作用机制，寻找影响锂离子脱嵌的关键步骤以及氧离子进行可逆电化学反应的决定性因素。此外，研究充放电过程中材料表面结构演变规律，建立离子扩散、电荷补偿和表面性质与电化学性能之间的“构效”关系，为高容量正极材料的开发提供新思路和科学依据。

高容量正极材料的开发是锂离子电池领域的重要课题。传统认为良好有序晶体结构、阳离子混排少是获得优异电化学性能的前提。然而，近期发现的阳离子无序岩盐结构富锂正极材料可通过逾渗网络进行锂离子的快速迁移，扩展了高容量正极材料的设计思路。在本项目的支持下，探讨了阳离子无序Li2TiO3基富锂正极材料的制备方法，并针对其导电性差和循环性能不足的缺点，进行了碳包覆和F掺杂。此外，本项目同时研究了阳离子有序Li2MnO3基富锂正极材料，并对其进行表面改性：1）构筑尖晶石结构且贫镍表面可赋予材料优异倍率特性和良好的电压稳定性；2）聚吡咯表面修饰并诱导表面形成尖晶石相进一步提高材料倍率性能。本项目重点研究锂离子在有序/无序结构材料中的脱嵌机理，特别是锂离子在逾渗网络中的扩散动力学和氧离子参与电荷补偿作用机制，分析了影响锂离子脱嵌的关键步骤以及氧离子进行可逆电化学反应的决定性因素。此外，研究充放电过程中材料表面结构演变规律，建立离子扩散、电荷补偿和表面性质与电化学性能之间的“构效”关系。