高性能富锂层状材料构建及长循环阴离子氧化还原反应机制研究

The anomalously high capacities of Li-rich materials are a result of contributions from both cationic and anionic redox processes, however，anionic redox also leads to capacity loss and structural degradation, which limited the study of the mechanism of anionic redox in longer cycles. By regulating the degree of participation of anions in the electrochemical reaction, and seeking a balance between stability and capacity, it is an effective way to obtain the next generation of commercial cathode materials with high stability and high capacity. Our previous study has shown that changing the combination of lithium ions and transition metal ions with oxygen ions can affect the anion redox. This study aims to investigate the mechanism of anionic redox in longer cycles. The study mainly includes three parts as follows: (1) obtain a Li-rich layered material with high stability and high capacity by the anti-site defect design; (2) clarify the mechanism of anti-site defect regulation on balancing the stability and high capacity; (3) reveal the mechanism of anionic redox in longer cycles. The study will provide theoretical support for the acquisition of high-performance Li-rich layered materials and the supplement of anionic redox theoretical.

富锂层状材料具有高的容量是由阳离子和阴离子氧化还原反应贡献，但阴离子氧化还原反应的参与导致材料结构转变和容量衰减严重，限制了对长循环阴离子氧化还原反应机制的研究。通过调控阴离子参与电化学反应的程度，在稳定性和容量间寻求平衡，是获得下一代商业化正极材料兼具高稳定性和高容量的重要途径。预实验发现，改变锂离子和过渡金属离子与氧离子的作用方式能够影响阴离子氧化还原反应的进行。本研究旨在探讨长循环下阴离子氧化还原反应的作用机制，主要包括3部分研究内容：（1）基于反位缺陷设计获得兼具高稳定性和高容量的富锂层状材料；（2）阐明反位缺陷调控对平衡稳定性和高容量间的作用机制；（3）揭示富锂层状材料长循环下阴离子氧化还原反应的作用机制。本项目的开展将为高性能富锂层状材料的获得和丰富阴离子氧化还原反应理论体系提供支撑。

富锂层状材料具有成本低和能量密度高等优点，但循环过程中电压和容量快速衰减限制了其商业化的进程。本项目基于缺陷工程角度对富锂层状材料进行改性研究，采用改变过渡金属离子比例、引入锂缺陷、Nb掺杂过渡金属离子位等方法对其进行研究。上述结果表明通过改变局部晶体结构，提升了富锂层状材料倍率性能以及循环稳定性，减缓了循环过程中电压和容量快速衰减。同时，开发了一种简单和有效的高温后处理方法构建表面层状/尖晶石异质结构的富锂层状材料，对后处理温度和后处理时间进行了优化，发现LR-850样品具有最优异的循环稳定性，在5C倍率下循环600次的容量保持率为96.66%，700次的容量保持率高达92.2%。通过研究发现，改善晶体结构中Li-O-Li和Li-O-TM骨架含量，能够调控充放电过程氧离子氧化还原产物，从而提高长循环性能下氧离子参与电化学反应的程度。本研究能够为富锂层状材料商业化应用提供了理论参考和数据支撑。