Why LiFePO$_{4}$ is a safe battery electrode: Coulomb repulsion induced electron-state reshuffling upon lithiation

We performed systematic experimental and theoretical studies based on soft X-ray emission, absorption, and hard X-ray Raman spectroscopy of Li$_{x}$FePO$_{4}$. The results show a non-rigid electron-state reconfiguration of both the occupied and unoccupied Fe-3d and O-2p states during the (de)lithiation process. The critical 3d electron state configurations are consistent with the calculations based on MBJGGA+U framework, which improves the overall lineshape prediction compared with the conventionally used GGA+U method. The combined experimental and theoretical studies show that the non-rigid electron state reshuffling guarantees the stability of oxygen during the redox reaction throughout the charge and discharge process of LiFePO$_{4}$ electrodes, leading to the intrinsic safe performance of the electrodes. Work supported by the US DOE.