钠离子电池单晶P2型正极材料设计及反应动力学调控

构筑微米级单晶体是抑制电极材料微裂变和提高热力学稳定性的有效策略，然而较大单晶尺寸会增大氧化还原反应中载流子平均自由程，降低电极反应动力学和电化学性能。本项目提出基于含锂尖晶石过渡相调控多元素热力学稳定性差异和晶体生长动力学，可控制备微米级锂掺杂单晶P2型锰基正极材料，其中TM层锂掺杂可抑制高电压下P2−O2相变，并且锂掺杂诱导形成的Ni2+/3+混合价态也可提高单晶电子导电性；其次基于MoO3与主体材料间固溶体反应调控单晶微结构，构筑晶粒表面贫钠区和内部富钠区，钠离子浓度差形成有助于驱动电化学反应中Na+快速迁移。因此，本项目通过锂掺杂单晶构筑及其结构调控，以期实现微裂变抑制和反应动力学改善，并借助密度泛函理论计算研究锂掺杂和钠离子浓度差对于电子能态密度和Na+迁移势垒的影响规律，阐明结构调控改善单晶电极反应动力学的作用机理，可为钠离子电池电极材料单晶化构筑及结构调控与改性研究提供指导。

Building micron-sized single crystal is an effective strategy to suppress the microcrack and improve the thermodynamic stability of electrode materials. However, the large size of single crystal will enlarge the mean free path of carrier during redox reactions, which further reduce their kinetics and electrochemical performance. In this project, lithium containing spinel as a transition phase is proposed to regulate the differences in thermodynamic stability of multiple elements and the kinetics of crystal growth for the controllable preparation of lithium-doped micron-sized single crystal P2-type manganese-based cathode materials. Lithium dopping into TM layer can suppress the phase transition of P2−O2 at high voltages and enhance the electronic conductivity by inducing the formation of mixed valence states of Ni2+/3+. Besides, the solid solution reaction between the host materials and MoO3 is proposed to regulate the microstructure of single crystal. The sodium-rich bulk and sodium-poor surface in the single crystal grains are expected. The difference of sodium-ion concentration will drive the fast migration of Na+ during electrochemical reactions. Therefore, this project involved the build of single crystal and their structural regulation is expected to suppress the microcrack and improve the kinetics. And the density functional theory is used to study the effect of lithium dopping of single crystal on their electronic density of states. The effect of sodium concentration difference on the Na+ migration barrier is also studied. Based on these results, the mechanism of improved reaction kinetics of single crystal electrode by structural regulation is clarified. These achievements will offer new insights into building the single crystal electrodes and their structural regulation along with modification investigation for sodium ion batteries.