锂离子电池正极材料LixNi0.5Mn0.5O2电子结构的第一性原理研究

采用基于密度泛函理论的第一性原理超软贋势平面波法，对LixNi0.5Mn0.5O2的几何结构进行优化，并计算相应的电子结构和平均嵌锂电压.结果表明：x=1时，费米能级上分布着Ni、Mn d轨道电子和部分O2p轨道电子，层状LiNi0.5Mn0.5O2是电子的良导体；O2p轨道与Ni、Mn形成较强的共价键， Ni-O与Mn-O具有相近的键长，抑制了LiNiO2与m-LiMnO2中的因Jahn-Teller效应导致的八面体扭曲，且Mn-O键长在充放电过程中保持不变，材料具有稳定的结构；Li在晶胞中以主要离子态的形式存在，有利于脱嵌与传输.随着锂离子的脱出，材料的带隙增加，导电性能变差.

First principles study on electronic structure of Li xNi0.5Mn0.5O2 cathode material for lithium ion batteries

The geometries of LixNi0.5Mn0.5O2 was optimized by density functional theory (DFT) plane-wave ultrasoft-pseudopotential method, and then the corresponding electronic structure and average intercalation-Li voltage were calculated. The results indicate that when x=1, the d orbital electron of Ni, Mn and part of O2p near the fermi surface are electronic contributors; O2p and Ni (Mn) 3d orbials form strong covalent bonds. The bond length of Ni-O is similar to that of Mn-O, which inhibits the distorting of M-O octahedron. LiNi 0.5Mn0.5O2 is not only a good electric conductor but also owns stable structure. Li exists in layer material mainly in the state of Li+, which is conducive to deintercalation and diffusion. The electrical conductivity gradually becomes poor with the deintercalation of Li-ion and the increase of band gap.