钠离子电池P2相层状正极材料表面衰退的原子机制及改性研究

钠离子电池P2相层状正极材料因具有较好的结构稳定性和倍率性能而受到广泛关注。申请人在前期工作中发现晶内裂纹是P2相层状正极材料高电压下性能衰退的主要原因；与元素均匀掺杂相比，掺杂元素原位偏聚形成的沉淀相能够更有效地抑制晶内裂纹，提升循环稳定性；然而，沉淀相强化的层状正极材料在长循环后表面区域沉淀相会发生退化，导致表面裂纹等衰退，限制循环稳定性的进一步提升。目前尚缺少分析P2相层状正极材料表面衰退的原子机制研究。本项目将利用电子显微学分析方法，在原子尺度下研究P2相层状正极材料表面结构演化，阐明表面衰退机理，揭示元素掺杂抑制表面裂纹形核生长机理，筛选能够有效抑制表面裂纹的正极材料。在此基础上，构建以具有稳定表面的正极材料为壳，以沉淀相强化的正极材料为核的核壳结构，调控核壳比例，获得具有最佳循环稳定性的正极材料。本项目研究将为设计高电压下具有稳定结构的高性能层状正极材料提供理论依据和实验探索。

The P2 layered cathode materials for sodium-ion batteries have been attracting growing attention from researchers because of their good structural stability and rate performance. The applicant’s previous work shows that intragranular crack is the main cause of performance decay in the P2 layered cathode materials during high voltage cycling. Compared with uniform doping, the applicant shows that the precipitates formed by dopant segregation can further suppress intragranular cracks and improve cycling stability. However, the precipitates at the surface region suffer from degradation in the P2 layered cathode materials strengthened by the precipitates after a long cycle, which results in surface degradation and limits the improvement of cycling stability. And there is still a lack of investigation on the atomic mechanism of surface degradation for P2 layered cathode materials. In this proposal, we will apply transmission electron microscopy to investigate the surface structure evolution of the P2 layered cathode materials at the atomic level and clarify the surface degradation mechanism. This proposal will reveal the nucleation and growth mechanism of surface cracks in elemental doped cathodes, and pick out the cathode materials that can effectively suppress the surface cracks. Based on the study of surface degradation mechanism, this proposal is intended to construct a core-shell structure, in which the cathode stabilizing the surface acts as the outer shell, and the cathode strengthened by the precipitates acts as the inner core. This proposal will also adjust the core/shell ratio and optimize the cycling performance. This proposal will provide the experimental and theoretical basis for the rational design of high-performance layered cathode materials with stable structures operated at high voltage.