Abstract Doping transition metal ions in LiCoO2 batteries has been proved an efficient method to improve the electrochemical properties in experiment, which is deeply related with the distorted local structure of impurities ions. According to the observed EPR spectra, the distorted local structures for 3d3 (Mn4+), 3d5 (Fe3+) and 3d7 (Ni3+) ions in LiCoO2 batteries are theoretically studied based on the perturbation calculations of Spin Hamilton Parameters (g factors, hyperfine structure constants A and Zero-field splittings parameters D and E). By considering the Jahn-Teller effect and mismatch radius of above transition metal ions (TMs), the formed [MnO6]8-, [FeO6]9- and [NiO6]9- clusters in LiCoO2 exhibit various distorted symmetries compared with experimental single one, characterized by trigonal distortion parameter Δθ as well as rhombic distortion parameters ΔZ and Δφ in the 3d3 center and the 3d5 center and tetragonal distortion parameter ΔZ in the 3d7 center. In addition, compared with asymmetrical signal of EPR spectra at 30K, the role of relatively high temperature for 100K is investigated by dynamic Jahn-Teller, making the isotropic EPR signal and regular octahedron for Ni3+ center. Comparing with the obtained structure properties of isolate-doped transition metal ion, the co-doped Mg in LiCoO2 makes the further elongated distortion of local structure. Based on the well fitted EPR parameters and obtained local environment of doped transition metal ions, the inactive of electrochemical properties of Mn4+ can be attribute to the largest crystal field (Dq) and the smallest difference with host Co3+ site. Therefore, a comprehensively study of the local structure may be helpful to understand and predict the electrochemical behaviors of batteries.

中文翻译：

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层状 LiCoO2 正极材料中 3d3、3d5 和 3d7 离子的局部结构研究

摘要 在LiCoO2电池中掺杂过渡金属离子已被实验证明是一种提高电化学性能的有效方法，这与杂质离子局部结构的扭曲密切相关。根据观察到的EPR光谱，基于自旋哈密顿参数（g因子，超精细结构常数A）的微扰计算，理论研究了LiCoO2电池中3d3（Mn4+）、3d5（Fe3+）和3d7（Ni3+）离子的局部结构畸变和零场分裂参数 D 和 E)。通过考虑上述过渡金属离子 (TMs) 的 Jahn-Teller 效应和失配半径，LiCoO2 中形成的 [MnO6]8-、[FeO6]9- 和 [NiO6]9- 簇与实验中的单个簇相比表现出各种扭曲的对称性, 其特征在于3d3中心和3d5中心的三角畸变参数Δθ以及菱形畸变参数ΔZ和Δφ以及3d7中心的四方畸变参数ΔZ。此外，与EPR光谱在30K的不对称信号相比，动态Jahn-Teller研究了100K相对高温的作用，使Ni3+中心为各向同性的EPR信号和正八面体。与所获得的孤立掺杂过渡金属离子的结构性质相比，LiCoO2中的共掺杂Mg使局部结构进一步拉长畸变。基于拟合良好的 EPR 参数和获得的掺杂过渡金属离子的局部环境，Mn4+ 的电化学性质的非活性可归因于最大的晶场 (Dq) 和与宿主 Co3+ 位点的最小差异。