Resonant Photoemission Spectroscopy of the Cathode Material LixFePO4 for Lithium Ion Battery

The change of Fe 3d states accompanied with the Li intercalation/deintercalation process has been successfully revealed by resonant photoemission spectroscopy. The main peak shift and expansion of Fe 3d bands through the Li deintercalation reflect the strong hybridization between Fe 3d states and O 2p states as the Fe–O bond lengths decrease. From the antiresonance spectra, O 2p partial density of states also changes, suggesting the interaction between Fe and O atoms still remains in LiFePO4. Furthermore, density functional theory calculations results strongly support these experimental results. The framework structure of LiFePO4 is more suitable than that of LiCoO2 for the good rechargeable battery, because the change of the electronic structure in LiFePO4 valence band is rather small because of the strong covalent P–O bond.