In situ X-ray absorption spectroscopic study for the electrochemical delithiation of a cathode LiFe 0.4Mn 0.6PO 4 material

Abstract

The electronic and local atomic structural characterization of a promising cathode material, LiFe 0.4Mn 0.6PO 4, for a lithium rechargeable battery was performed by in situ X-ray absorption fine structure (XAFS) on both Mn and Fe K-edges. Upon delithiation, the X-ray absorption near edge structure (XANES) spectra analysis showed that the Fe 2+/Fe 3+ electrochemical reaction was two times faster than that of Mn 2+/Mn 3+. The Fe and Mn K-edge extended X-ray absorption fine structure (EXAFS) spectra were effectively altered with different spectral behaviors for the local atomic structure near Fe and Mn during delithiation. Alternatively, the EXAFS spectra of LiFePO 4 changed significantly and those of LiMnPO 4 were constant through all delithiations for the corresponding reference materials of LiFePO 4 and LiMnPO 4. The present study with XAFS characterization demonstrates that initially delithiated Fe-rich domains at 3.5 V can promote more effective local structural change of the neighboring Mn-rich domains during the next second plateau at 4.1 V, which can ease delithiation in the Mn-rich domains through more flexible reaction of the local structure in the Mn octahedra.