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(Fe_1−xMe_x)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 Fe_1−xAg_x moves into its conduction bands (CBs) due to the Ag doping. The Li(Fe_1−xAg_x)PO₄ system displays the periodic direct semiconductor characteristic with the increase of Ag-doped concentration. However, for Fe_1−xMn_x 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(Fe_1−xMn_x)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. Supported by the National Natural Science Foundation of China (Grant No. 50771046), the Natural Science Foundation of Guangdong Province (Grant No. 05200534), and the Key Projects of Guangdong Province and Guangzhou City (Grant Nos. 2006A10704003 and 2006Z3-D2031)