A First-Principles Study of F and Cl Doping in LiNi_0.8₃Co_0.₀₈Mn_0.₀₈O₂ Cathode Materials

Ion doping can modify the cell structure, which is one of the effective methods to improve electrochemical performance. However, there is a lack of research on F- and Cl-doped LiNi0.8Co0.1Mn0.1O2. In this paper, the effects of F and Cl doping on the electrochemical properties and cell structure of LiNi0.83Co0.08Mn0.08O2 during the process of lithium removal were studied by a first-principles calculation based on density functional theory. The results show that F doping reduces the change in cell parameters and improves the stability of cell structure. On the contrary, Cl doping reduces the stability of the cell structure. F doping increased the delithiation potential from 3.64 V to 3.76 V, and the delithiation potential was relatively stable in the process of delithiation. Cl doping decreased the delithiation potential from 3.64 V to 3.26 V, and the voltage stability became worse. F doping can effectively reduce the occurrence of Li–Ni mixed arrangement phenomena. Meanwhile, Cl doping can inhibit the formation of oxygen vacancies, and the further degradation of the materials. F doping broadens the Li+ diffusion channel away from the doping site and improves the diffusion rate of Li+ in this layer. In the vicinity of F-doped sites, the electrostatic field in the process of Li+ diffusion is enhanced and the diffusion of Li+ is reduced. Cl doping increases the diffusion barrier of Li+ and slows down the diffusion rate of Li+