LiM_xMn_(2-x)O_4正极材料的表面改性机理研究

Surface Modification Mechanism of Spinel Structure LiM_xMn_(2-x)O_4 as Cathode Materials for Lithium Ion Batteries

采用溶胶-凝胶包裹法对尖晶石LiMn_2O_4及其阳离子掺杂LiM_(0.1)Mn_(1.9)O_4(M=Li,Ni)正极材料进行了表面改性研究.X射线衍射及电子探针线扫描分析表明,表面改性以后的晶粒仍为尖晶石结构,表面改性离子Co的浓度由表及里逐步减小.电解液溶蚀实验及电化学循环测试表明,表面改性后的正极材料LiM_(0.1)Mn_(1.9)O_4的抗溶蚀性明显增强,循环性能优良.性能改善的原因是表面改性以后,尖晶石晶粒表层Mn^(3+)离子浓度降低,Mn^(4+)离子浓度大大增加,减少了Mn^(3+)发生歧化反应的机会.

The grains of LiMn2O4 and LiMxMn2-xO4 (M=Li, Ni) were coated with LiCoO2 by using sol-gel process. XRD and EPMA studies confirme the presence of a Co-rich spinel LiMn2-xCoxO4 layer on the surface of LiMxMn2-xO4 grains and the content of Co decreases gradually from the surface to the core of spinel grains. Furthermore, the amount of Mn3+ in the surface layer is less than in the core, so the possibility of Mn dissolution decreases. The surface treatment is effective in reducing the rate of Mn dissolution into electrolyte and improving cyclability of spinel LiMxMn2-xO4 cathode materials. After bulk Ni-doped spinel LiNi0.1Mn1.9O4 coated with LiCoO2, the cyclability of the material is better than that of pure spinel LiMn2O4 and just only cations doped.