Large Charge-Transfer Energy in LiFePO4 Revealed by Full-Multiplet Calculation for the Fe L3 -edge Soft X-ray Emission Spectra.

We analyzed the Fe 3d electronic structure in LiFePO4 /FePO4 (LFP/FP) nanowire with a high cyclability by using soft X-ray emission spectroscopy (XES) combined with configuration-interaction full-multiplet (CIFM) calculation. The ex situ Fe L2,3 -edge resonant XES (RXES) spectra for LFP and FP are ascribed to oxidation states of Fe2+ and Fe3+ , respectively. CIFM calculations for Fe2+ and Fe3+ states reproduced the Fe L3 RXES spectra for LFP and FP, respectively. In the calculations for both states, the charge-transfer energy was considerably larger than those for typical iron oxides, indicating very little electron transfer from the O 2p to Fe 3d orbitals and a weak hybridization on the Fe-O bond during the charge-discharge reactions.