Li2FePO4F and its metal-doping for Li-ion batteries: an ab initio study†
Abstract
The electrochemical properties of three isotopic Li2FePO4F compounds, as cathode materials under different space groups Pbcn, P and Pnma were investigated using first principle calculations. Their structures and average open circuit voltages for step delithiation reactions were explored, and the results are in good agreement with the reported experimental data. We estimate the substitution effect of Fe by Co in Pnma-Li2FePO4F. The substitution of Fe by Co in Li2Fe1−xCoxPO4F may enhance the discharge potential of the materials, and the rate of its volume change during the redox process is between 0.6% and 2.1%. Furthermore, from the projected density of states for Li2Fe0.5Co0.5PO4F, we found strong hybridization for Fe-3d and Co-3d bands near the Fermi level, which implies that the Co-doped Li2Fe1−xCoxPO4F may possess better electronic conductivity than the pure phase.