The Spin-Polarized Electronic Structure of LiFePO4 and FePO4 Evidenced by in-Lab XPS

Abstract

LiFePO4 has an interesting spin-polarized electronic structure showing a (3d↑)5(3d↓)1 electron configuration of the Fe2+ ion. In this work, we have experimentally evidenced the valence electronic structure of LiFePO4 and of its delithiated compound FePO4 by X-ray photoelectron spectroscopy (XPS), which allows a visualization of the occupied densities of states (DOS) in the valence band. XPS valence spectra were compared with the DOS obtained from DFT calculations by considering GGA and GGA + U approaches. Thanks to electrochemical extraction/insertion of Li+ ions in LiFePO4/FePO4, it was possible to display the Fe 3d spin-down electron of LiFePO4, which is not present in the valence spectrum of FePO4. We show that the study of XPS valence spectra is an efficient way to access the lithium insertion rate in LixFePO4 positive electrode materials for lithium-ion batteries. Besides the contribution to the Li-ion battery field, this paper is also a rare example of experimental evidence of a spin-resolved electr...