First-principles study of LiFePO4 modified by graphene and defective graphene oxide

Abstract

The energy stability and electronic structural of graphene and defective graphene oxide (GO) parallel to the surface of LiFePO₄ (010) were theoretically investigated by using first-principles density functional theory calculations within the DFT + U framework. The calculated formation energy shows that GO coating on the surface of LiFePO₄ (010) is energetically favorable and has higher bond strength compared to graphene. The calculation of the electronic structure indicates that the emergence of band in-gap states originates from graphene coating, with adsorbed O atoms contributing significantly above the Fermi level. Electron density difference indicate that GO stands on the LFP (010) surface through C-O and Fe-O bonds, rather than relying on van der Waals forces placed parallel to the LFP crystal, with the chemical bond at the LFP/GO interface (Fe-O-C) both anchoring the coated carbon layer and promoting electron conductivity at the interface. In addition, LFP/GO shows superior electrochemical performance, Atomic Populations suggests that the average Fe-O bonding on the surface of LiFePO₄ (010) was clearly changed after graphene or GO coating, which led to the expansion of Li⁺ channels and favored the migration insertion and extraction of Li⁺.

Keywords: Defective graphene oxide; Density of states; First-principles; LiFePO(4).