Ab initio study of the effects of Ag/Mn doping on the electronic structure of LiFePO4

Based on density functional theory (DFT) of the first-principle for the cathode materials of lithium ion battery, the electronic structures of Li(Fe1 xMex)PO4 (Me = Ag/Mn, x = 0–0.40) are calculated by plane wave pseudo-potential method using Cambridge serial total energy package (CASTEP) program. The calculated results show that the Fermi level of mixed atoms Fe1 xAgx moves into its conduction bands (CBs) due to the Ag doping. The Li(Fe1 xAgx)PO4 system displays the periodic direct semiconductor characteristic with the increase of Ag-doped concentration. However, for Fe1 xMnx mixed atoms, the Fermi level is pined at the bottom of conduction bands (CBs), which is ascribed to the interaction between Mn(3d) electrons and Fe(4s) electrons. The intensity of the partial density of states (PDOS) near the bottom of CBs becomes stronger with the increase of Mn-doped concentration. The Fermi energy of the Li(Fe1 xMnx)PO4 reaches maximum at x = 0.25, which is consistent with the experimental value of x = 0.20. The whole conduction property of Mn-doped LiFePO4 is superior to that of Ag-doped LiFePO4 cathode material, but the structural stability is reverse.