First-principles investigation of the electronic and Li-ion diffusion properties of C and B doped LiFePO4 (0 1 0) surface

Abstract

The electronic structure and Li-ion diffusion properties of the surface of LiFePO4 (010) doped with C and B elements were investigated using a first-principles approach based on density universal function theory. Calculations of the formation energy show that the surface defect energy decreases after the dopant replaces the oxygen, which is in accordance with the thermodynamic stability criteria. The difference in charge density indicates that the doped atoms on the modified surface form stronger covalent bonds with adjacent Fe atoms, while the density of states study shows that the introduction of C and B elements narrows the forbidden band of LiFePO4 and exhibits better electronic conductivity. In addition, we calculate the energy barrier for the diffusion of Li-ions along the b-channel of the (010) surface using a transition state search method. The results show that the doped system possesses a lower energy barrier, which suggests that the doping of C and B elements reduces the limitation of Li-ion migration to the surface and increases the Surface diffusion rate. At the same time, we find that element B performs better than element C in improving surface conductivity and Li-ion surface diffusion .