锂离子电池电极材料性能调控的界面效应研究

New-type electrode materials of Li ion batteries such as Li-rich and olivine cathode materials, metal oxide anode materials, etc. have great application potential.However, their stability, cycling and rate performances require to be further improved. Doping and graphene coating are the hot research topics to modulate the electrochemical performances of electrode materials. The surfaces and grain boundaries in electrode materials, as well as the interfaces between the electrode materials and the coating, play an important role in the control of the electrochemical performances of the electrode materials. The microscopic mechanism of the interface influence on the electrochemical properties is a scientific problem urgent to be solved. In this project, we will focus on the Li-rich and olivine cathode materials and metal oxide anode materials to systematically study the effects of surfaces and grain boundaries of electrode materials and the interfaces between the electrode materials and graphene, as well as the dopants at the interface, on the electrochemical properties of the electrode materials, using first-principles calculations. The atomic structures of the interfaces will be obtained and the electronic structures of the systems will be analyzed. In combination with the electrochemical performance test of electrode materials with different dopants and graphene coating, the microscopic influence mechanism of the interface, as well as the dopants at the interface, on the electrochemical properites of the electrode materials will be made clear. The interface effects in the electrochemical performance modulation of the electrode materials will be elucidated. Furthermore, through this project, the redox processes during the Li ion intercalation and deintercalation will be comprehensively understood. Thus, the relationship of the electrochemical performances of the eletrode materials with doping and graphene coating is expected to be established, which will direct the optimization of sythesis conditions to control the doping and coating and to realize the interface modulation, and as a result, the eletrochemical performance of the electrode materials will be enhanced, and new-type electrode materials in Li ion batteries will be designed.

富锂正极材料、橄榄石型正极材料、金属氧化物负极材料等新型锂离子电池电极材料具有重要应用潜力，但是其稳定性、循环和倍率性能等需要改进，掺杂和石墨烯包覆是调控其电化学性能的研究热点；性能调控中，表面、晶界以及石墨烯包覆层与电极材料间界面起着重要作用，但界面对材料电化学性能的微观作用机制尚不清楚。本项目采用第一性原理计算系统研究富锂和橄榄石型正极材料、金属氧化物负极材料的表面、晶界、与石墨烯间界面，以及界面掺杂对体系电化学性能的影响；确立界面的稳定原子构型和电子结构，并结合实验对不同掺杂和石墨烯包覆材料的电化学测试，探明界面及界面掺杂影响电化学性能的微观机制，阐明电极材料性能调控的界面效应，并深入理解锂离子脱嵌过程中氧化还原过程。建立掺杂、石墨烯包覆与电极材料电化学性能间的关系，研究结果对于通过掺杂和包覆，实现界面调控，提高电极材料的电化学性能，设计优化新型锂离子电池电极材料具有重要指导意义。

本项目针对锂离子电池富锂正极材料、橄榄石型正极材料和金属氧化物负极材料，研究电极材料中的界面及其与石墨烯的界面和界面掺杂对体系电化学性能的影响；并结合电池材料的研究进展，扩展研究了金属硫化物负极材料和普鲁士蓝正极材料及其储锂（钠）行为。系统研究了石墨烯与电池正极和负极材料组成纳米复合电极材料中的界面储锂（钠）效应，分析了锂（钠）离子脱嵌过程中体系的稳定性和电子转移，探明了界面储能机制，获得了界面储能对容量的贡献，并解释了石墨烯基复合电极材料的储能容量高于理论值的原因；阐明了界面结合与界面储锂（钠）协同效应的关系，发现界面中锂（钠）原子吸附和扩散的协同增强作用与界面结合密切相关；并对体系导电性能进行了分析。研究了掺杂对界面电子结构和界面结合的影响，探明了掺杂对锂离子吸附和扩散的影响规律，确立不同掺杂元素的掺杂效应，并提出了通过具有不同掺杂效应的掺杂元素共掺改进体系电化学性能的途径。研究了富锂正极材料中相界面和掺杂对体系电化学性能的影响，发现Li2MnO3/LiMO2界面的非对称性，有利于富锂材料保持较高平均电压，有利于材料的稳定性，进而提高材料的容量。掺杂与Li2MnO3相中O电子态的局域化程度相关，可改善富锂材料的失氧现象和提高材料的容量；通过对富锂材料表面进行相调控，发现MCNT-尖晶石相双相网络显著提高了表界面的电子和离子传输速率；将化学吸附法应用于正极材料的表面修饰中，制备得到的富锂正极材料具有双壳层表面修饰结构和优秀的高倍率循环性能。以纳米复合电极材料中界面和掺杂效应为指导，开展实验，制备了富含表界面的锂（钠）离子电池的电极材料；优化了工艺参数，通过复合和掺杂，实现了界面调控，获得了具有优异电化学性能的锂（钠）离子电池电极材料，表明获得的界面和掺杂效应等微观机制可指导锂（钠）离子电池电极材料的设计和开发。