Investigation on interfacial interaction and the origin of Fe3+ in LiFePO4/C

The nano-structural LiFePO4/C composites with different interfacial structures were investigated. Fe L-edge XAS spectra indicated that the formation of Fe3+ was related to the interfacial properties of the C-LiFePO4. C K-edge and O K-edge XAS spectra show a distinct bonding character between the carbon and LiFePO4 particle in carbon coated LiFePO4/C. Density functional theory (DFT) calculation was used to analysis the bonding character between the carbon and the LiFePO4 particle and to investigate the formation mechanism of Fe3+. The electrochemical properties are characterized by cyclic voltammograms, constant current charge–discharge, and electrochemical impedance spectra. And it was found that sample A with intimate LiFePO4/carbon interface shows better electrochemical performance than sample B with loose LiFePO4/carbon interface and sample C which had not chemical adsorption between carbon and LiFePO4 particles.