In situ X-ray absorption spectroscopic study for the electrochemical delithiation of a cathode LiFe_(0.4)Mn_(0.6)PO_4 material

摘要

The electronic and local atomic structural characterization of a promising cathode material, LiFe_(0.4)Mn_(0.6)PO_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.