An ab initio study of chlorine and fluorine doping on Li2FeSiO4 as cathode materials for Li-ion battery

Li₂FeSiO₄ (LFS) has received remarkable attention due to its high thermal stability, environmental benignity, low cost, and low toxicity. However, the electrochemical performance of the material is restricted by achieving its high theoretical capacity (∼330 mA h g⁻¹). Doping is a potentially effective method to enhance the electrical conductivity and performance, and to reduce the operation voltage of the LFS cathode material. In this study, using density functional theory (DFT), fluorine-doped LFS (Li₂FeSiO_3.5F_0.5) and chlorine-doped LFS (Li₂FeSiO_3.5Cl_0.5) are evaluated. The structural properties, structural stability after extraction of the lithium-ions, cycle ability, chemical stability, cell voltage, electrical conductivity, and rate capability are assessed for the considered cathode materials. These theoretical studies predict that F and Cl doping enhances structural stability, chemical stability, electrical conductivity, rate capability, and reducing cell voltages to put the material in the electrolyte voltage tolerance to extract two Li per formula. Accordingly, the results show that the doping increases the performance, rate capability, stability, and capacity of LFS.