富锂锰基正极材料锂/锂空位行为与电压衰减机理及调控研究

Li-rich layered oxides have attracted attentions as one of the most promising cathode materials for the requirements of the energy density of Li-ions batteries over 300 Wh/kg in electric vehicles. Although several methods have been succeeded in improving the initial coulombic efficiency and rate capability, these have not been as effective at mitigating voltage decay, even of which is essentially considered as the greatest obstacle for its practical application. The origin for this issue is lacking a clear understanding on the structural characteristics after the phase transition so far. In contrast to the research of the activities of lattice oxygen and transition metal, in this project, we focus on the Li/Li-vacancies behavior of the cycled samples, including normal sites, vacancies and interstitials. In particular, the effects of Li/Li-vacancies behaviors on the changes of the long-range structures will be investigated. Also the transformations of the local structures will be studied. Furthermore, the key factors that affect the thermodynamics and kinetics stability of the voltage decay will be discussed. Based on the above research, the correlations among crystal, Li/Li-vacancies behavior, and voltage decay can be built. It will further help us well understand the mechanism of voltage decay, and find some effective methods to counter the voltage decay. As a final goal, the present project will provide some theoretical foundations and technical guidance to design high performance layered Li-rich layered oxides. structure, Li/Li-vacancies behavior, and voltage decay can be built. It will further help us well understand the mechanism of voltage decay, and find some effective methods to counter the voltage decay. As a final goal, the present project will provide some theoretical foundations and technical guidance to design high performance layered Li-rich layered oxides.

富锂锰基正极材料被认为是实现300wh/kg以上动力锂电池最有前途的正极材料之一。虽然通过许多改性方法使该材料的首次效率和倍率性能得到明显的改善，但是还是无法有效抑制电压衰减的产生，甚至认为这是该材料实用化最大的障碍。其原因在于到目前为止对相变后的结构特征还没有一个清晰的认识。相对于目前的过渡金属和晶格氧的研究，本项目基于前期的研究结果，提出以循环后富锂锰基材料为对象，从锂和锂空位行为(包括正常锂格位，间隙以及空位位置) 角度去研究富锂材料电压衰减机理的研究思路。重点考察具有不同结构的富锂材料在充放电过程中其锂和锂空位行为对长程结构变化的影响以及局域结构相变的演变，探讨影响材料循环电压衰减的动力学和热力学稳定性的关键因素。通过这些研究，建立富锂材料体相结构、锂和锂空位行为和电压衰减三者之间的内在联系，揭示电压衰减机理，从而找到有效的方法去抑制电压衰减，为设计具有更高性能的新型富锂正极。

富锂锰基正极材料被认为是实现300wh/kg以上动力锂电池最有前途的正极材料之一。但是其在充放电循环过程中充产生的电压衰减行为成为该材料实用化的最大障碍。本项目相对于目前的过渡金属和晶格氧的研究，从锂和锂空位行为角度去研究富锂材料电压衰减机理。通过探索影响富锂锰基正极材料中晶格氧活性与氧缺陷之间的关联作用，提出了利用体相层错实现氧活性、抑制氧气释放的方法，利用原位加热/加压的同步辐射X射线衍射方法，揭示了材料的结构亚稳定性和结构柔性，通过增加体相高浓度氧缺陷实现了富锂锰基正极材料低的电压衰减，发现了Ni2+离子容易在材料中发生偏聚并形成传统层状相，而Co3+离子可以部分地参与Li2MnO3相的形成，影响Li2MnO3相中晶格氧氧化还原的电荷转移路径，有效地促进晶格氧活化，探索了富锂锰基正极材料在高能量密度电池中应用。研究结果对于解决富锂锰基正极材料的关键科学/技术问题具有重要的指导作用。