锂离子电池层状氧化物正极材料的结构调控与中子衍射研究

Cations migration, Li-metal cation intermixing and the resultant phase transition are mainly responsible for the performance degradation of high specific capacity LiNixMnyCo1-x-yO2（NCM）or Li-rich layered oxides as cathodes for lithium-ion batteries. Elemental doping or surface modifications are the main modification approaches. But the modification mechanism is still not very clear. For examples, what are the effects of the elemental doping or surface modifications on cation migration or Li-metal cation intermixing? What kind of cations will intermix with Li? How about the relationship between Li-metal cation intermixing and electrochemical performance? It is significant to clarify these questions for the exploration of new and efficient improvement methods. Neutron is sensitive to light elements (H, Li, et al.) and can distinguish neighbor atoms (Fe, Ni, Co, et al). Herein, this project will be focused on studying the effects of elemental doping (Mg, Al, Na, Ti, Y, et al.) or surface modification (Li-ion conductive Li2M’O3, M’=Ti, Zr, Si, et al.) on cation migration or Li-metal cation intermixing, structure stability and electrochemical performances of LiNixMnyCo1-x-yO2（NCM）or Li-rich layered oxide cathodes via neutron diffraction as well as XPS,SEM/TEM and electrochmical tests. The elemental doping or Li2M’O3 coating-cation migration or Li/M mixing-electrochemical performances relationship will be analyzed and the modification mechanism will be further studied, which will be helpful for the structure design and the performance optimization of LiNixMnyCo1-x-yO2（NCM）or Li-rich layered oxides cathodes for lithium-ion batteries.

阳离子迁移、Li/M(M=过渡金属)交互占位及由其引起的结构相变是影响三元或富锂锰基层状氧化物正极材料性能的重要原因。元素掺杂和表面包覆是两种主要改性方法，但是其改性机理还有待深入研究，如：元素掺杂或表面包覆对Li/M混排有何影响？哪些阳离子会发生迁移或混排？Li/M混排程度与电化学性能之间的关系如何？而弄清这些问题对开发高效改性方法具有重要意义。本项目将利用中子对轻元素敏感、能区分相邻元素等特点，通过中子衍射，并结合XPS、 电镜、电化学测试、阻抗分析等方法研究Mg、Al、 Na、Ti、 Y等元素掺杂和锂离子导体Li2M’O3包覆（M’=Ti、Zr、Si等）对三元或富锂锰基层状正极材料阳离子迁移、Li/M混排、结构稳定性及电化学性能的影响，分析元素掺杂或Li2M’O3包覆-阳离子迁移或Li/M混排-电化学性能之间的内在联系，深入研究其改性机理，并反馈指导正极材料的结构调控与性能优化。