径向有序核壳层状-尖晶石富镍材料的合成、形成机理及脱嵌锂机制研究

Ni-rich layered oxide cathodes are considered as the promising material for automotive lithium ion batteries. The key point for the commercial applications of the materials is increasing the cycling stability and safety. We expect to construct a spinel-layered heterostructured core-shell nickel rich cathode with radially oriented nanorod core in order to enhance the performance of material by integrating the advantages provided by stable spinel LiNi0.5Mn1.5O4 shell and radially oriented nanorod core. The preparation process would be firstly studied by optimizing parameters related to continuous coprecipitation and annealing process to realize the controlled synthesis. The formation process of hydroxides precursor during precipitation and spinel-layered heterostructured core-shell during annealing would be monitored to establish the formation mechanism involved in the two processes. The synergistic effect of spinel-layered heterostructure would be investigated by tracking the electrochemical reaction kinetics and structure evolution during de/lithiation. This study will pave a way to the research of other Ni-rich layered oxide cathodes with high performance.

富镍层状氧化物是当前高能量密度锂离子动力电池的理想正极材料。增加富镍层状氧化物的循环稳定性和安全性是其推向商业应用的关键。本项目构筑径向有序核壳层状LiNi0.8Co0.1Mn0.1O2@尖晶石LiNi0.5Mn1.5O4异质共生材料，以利用尖晶石LiNi0.5Mn1.5O4壳层和内核的径向有序择优生长来提高材料循环稳定性和安全性。通过考察连续化沉淀结晶及煅烧参数，探明材料合成工艺，实现其可控制备。通过对连续化共沉淀结晶形成前驱体和煅烧形成异质共生材料的追踪，明确核壳前驱体连续化共沉淀结晶及异质共生结构的形成机理。通过对充放电过程中异质共生结构的影响进行研究，确定异质结构脱嵌锂过程协同作用机制。本项目研究结果将为高性能富镍正极材料的相关研究提供数据参考和理论支撑。

富镍层状氧化物是高能量密度锂离子动力电池理想的正极材料。增加富镍层状氧化物的循环稳定性和安全性是其推向商业应用的关键。项目构筑径向有序核壳异质共生富镍正极材料，以利用异质共生壳层和径向有序择优生长的内核来提高材料循环稳定性和安全性。研究了连续沉淀结晶条件对系列NixCoyMz(OH)2 (x≥0.8)前驱体一次晶粒径向有序的影响。无孪晶形成及TM离子完全沉淀下，可耦合较小的pH值、较大的氨、较低的搅拌强度调控二次颗粒和一次晶粒，构建径向有序前驱体。径向结构NixCoyMnz(OH)2 (0.8≤x≤0.9)适宜的pH值为11.1~11.3、氨盐比为1~4。研究了前驱体连续沉淀结晶演化机制。二次颗粒演化为：纳米片晶粒松散堆积的团聚体→团聚体增长融合形成二次颗粒→类球形二次颗粒→直径增大且粒径均匀分布的球形二次颗粒→含小粒径且具有较宽粒度分布的二次颗粒→粒度分布达到稳态。一次晶粒演化为：针状晶粒→持续变大且堆积更紧密的晶粒→新形成小晶粒。耦合条件及引入小粒径二次颗粒可抑制一次晶粒成核及新的二次颗粒团聚体形成，强化径向有序及粒度均匀性。研究了核壳及径向有序富镍正极高温锂化及机制。NixCoyMnz(OH)2(0.8≤x＜0.9)和NixCoyMnz(OH)2 (0.9≤x≤0.92)前驱体较优锂化温度为710~780℃和~730℃；Al引入降低富镍正极的锂化温度，Al含量越高，锂化温度越低。锂化结晶过程，晶体依次经历脱出自由水的p-3m1、含(104)L峰的NixCoyMnz(OH1-xLiy)2中间相、含O空位及Ni2+/Li+混排的R-3m、Ni2+/Li+有序性增加的层状相。锂化过程引入La、Mo元素可在晶粒表界面区域由内到外构建锂金属氧化物（氧化物）层、盐岩异质共生层。锂化过程引入B与Al、Ti、Zr元素组合可在不影响B调控径向有序下，强化结构稳定性。研究了核壳及径向有序富镍正极性能提升机制。核壳异质共生及径向有序结构可强化Li脱嵌过程H2↔H3相变可逆性、稳定晶体结构、减小晶胞体积收缩、抑制二次颗粒微裂纹及有害副反应，进而增强热稳定性及电化学性能。项目研究结果可为高性能富镍正极材料的相关研究提供参考。