强相互作用的阴阳离子共掺杂调控钠电池层状正极材料及其循环性能的影响机制

The application of sodium-ion batteries (SIB) in energy storage field is promising. Layered oxide cathode materials for SIBs presents many advantages and has been attracted extensive attentions. However, during the process of charging and discharging, the intercalation/deintercalation of sodium ions is always accompanied by the slip of the oxygen layers, which seriously lows cycle stability performance of the material. At present, the research strategy is focused on the doping of cations. Unfortunately, the preparation process of such layered cathode materials requires high temperature sintering under oxygen/air atmosphere which makes it difficult to dope with anions. By adding soluble sulfide to co-precipitation system followed by a special sintering process, we successfully synthesized a layered oxide cathode material with S doped. Moreover, it’s found that S doping in layered oxide could effectively reduce the cell changes along c axis during charge/discharge process, and thus greatly increased the cycle stability of cathode materials. So, in this project, co-doping with strongly bonded anion and cation to the layered oxide cathode materials is proposed in order to anchor adjacent two oxygen layers and thus inhibit the damage of material’s structure. Firstly, the co-doped cathode materials will be synthesized, and then the microstructure and chemical environment of sodium ion will be characterized by X-ray diffraction (XRD), solid state nuclear magnetic resonance (NMR), X-ray absorption fine structure, etc. Finally, relationship between structure and performance and mechanisms of action introduced by co-doping will be investigated by DFT theory, in situ XRD and XRD refinement, which provides theoretical and technical supports for the development of sodium-ions batteries.

钠离子电池在储能领域中的应用前景看好。层状过渡金属氧化物具有诸多优点，受到了广泛的关注，然而充放电过程中伴随着钠离子的嵌入/脱出发生氧层的滑移，致使材料结构变化，循环性能变差。目前研究策略集中在阳离子掺杂上，材料的制备工艺使得阴离子掺杂较为困难。申请人初步实验发现采用可溶性硫化物共沉淀法，结合改进的烧结工艺可将硫元素掺入层状正极材料，大幅增加材料的循环稳定性。基于此，本项目拟利用具有强相互作用的阴阳离子共掺杂层状正极材料，“锚定”相邻氧层，抑制其滑移，增强材料的循环性能。制备系列阴阳离子共掺杂的层状正极材料，探索掺杂离子对材料结构的调控机理，研究组成、配比等因素对材料循环性能的影响机制。采用XRD、固体核磁、X射线吸收精细结构谱等手段表征材料微观结构和钠离子化学环境，结合理论模拟研究充放电过程中结构演变机制，获取阴阳离子共掺杂引入的构效关系及影响机制，为钠电池的发展提供理论依据和技术支撑。

与锂离子电池相比，钠离子电池的钠源相对易得且价格低廉，使得其在储能领域中具有良好的应用前景。钠离子电池正极材料中，层状过渡金属氧化物具有诸多优点，如理论比容量高、合成工艺简单等，受到了广泛的关注。然而充放电过程中伴随着钠离子的嵌入/脱出发生氧层的滑移，致使材料结构变化，循环性能变差。为解决上述问题，提高材料的循环性能，申请人尝试并完成了如下工作：.1. 采用双模板剂辅助共沉淀法首先制备出分散的纳米片状前驱体，通过将前驱体与碱金属盐混合均匀烧结制备出层片状六边形形貌的P2型正极材料。.2. 通过对层状金属氧化物及掺杂正极材料的储钠性能研究，发现综合考察元素组成、元素价态和粉体形貌等特征对材料电化学性能的影响。.3. 掺杂改性的P2型正极材料机理探究：同副族元素中Au前驱体掺杂和同周期元素中Cu烧结掺杂，不仅可以保持结构为P2型纯相，且其相对较大的半径和低价态使TMO2层内的原子保持较大库仑引力，从而抑制层间滑移和Na+/空位产生。结合原位XRD技术和精修结果推测机理：晶胞参数沿c轴的扩大，同时降低过渡金属层的平均价态可提升Na+传输及改善P2型正极材料的电化学性能。通过掺杂低价态和大半径的离子，使TMO2层收缩及层间距增大，可降低Na+/空位产生、减小相邻原子层间的斥力和拓宽Na+扩散的通道。本研究结果可望为钠电池P2型正极材料的应用与改性提供支撑。