First-principles Investigation of the Electronic and Li-ion Diffusion Properties of LiFePO4 by Graphene Surface Modification

The structural, electronic and Li-ion diffusion properties of LiFePO4 (010) surface modified by graphene have been investigated by first-principles calculation under the DFT + U framework. The calculated formation energy indicates that the LiFePO4 (010) surface modified with graphene is energetically favourable. It is found that strong C-Fe and C-O covalent bonds are formed at the modified interface, and the band gap of LiFePO4 modified with graphene is narrowed, indicating better electronic conductive properties. The energy barrier for the diffusion of Li-ion along the b-channel perpendicular to the (010) surface is calculated using the method of finding the transition state. The results show that the energy barrier of the modified system is reduced, indicating that the surface modification of LiFePO4 by graphene can improve the surface diffusion rate of Li-ions.