First-principles study of structural, electronic and Li-ion diffusion properties of N-doped LiFePO4 (010) surface

The structural, electronic and Li-ion diffusion properties of N-doped LiFePO4 (010) surface have been investigated by first-principles calculation under the DFT + U framework. The calculated results show that the substitution of nitrogen for oxygen on the (010) surface of the LiFePO4 is energetically favored and N-substitution can significantly decrease the band gap of the LiFePO4, indicating better electronic conductive properties. The nudged elastic band (NEB) method is used to calculate the activation energy for Li-ion diffusion. It is found that for pure LiFePO4 (010) surface high intrinsic activation energy of Li-ion diffusion retards fast Li transport. However, this energy barrier can be effectively reduced by nitrogen surface modification. Our results imply that N doping on the LiFePO4 (010) surface could improve its electron conductivity and ion diffusion properties.