Resonant Photoemission Spectroscopy of the Cathode Material Li_xFePO₄ for Lithium Ion Battery

Abstract

The change of Fe 3d states accompanied with the Li intercalation/deintercalation process has been successfully revealed by resonant photoemission spectroscopy. The main peak shift and expansion of Fe 3d bands through the Li deintercalation reflect the strong hybridization between Fe 3d states and O 2p states as the Fe–O bond lengths decrease. From the antiresonance spectra, O 2p partial density of states also changes, suggesting the interaction between Fe and O atoms still remains in LiFePO4. Furthermore, density functional theory calculations results strongly support these experimental results. The framework structure of LiFePO4 is more suitable than that of LiCoO2 for the good rechargeable battery, because the change of the electronic structure in LiFePO4 valence band is rather small because of the strong covalent P–O bond.

Probing surface & transport phenomena in energy materials under operating conditions.

“…Consistent with previous reports, a change in the Fe oxidation state (from 2+ to 3+) upon de-lithiation shifts the main absorption feature in the Fe L 3 edge from ~ 708 to ~ 710 eV. [96][97][98][99][100] Other previously reported spectral features were also satisfactorily reproduced. Excellent fits were obtained at all spatial positions, with a maximum residual of 0.8 % (averaged over all photon energies).…”

Correlation between the O 2p Orbital and Redox Reaction in LiMn0.6Fe0.4PO4 Nanowires Studied by Soft X‐ray Absorption

“…Thus, the 3.45 V plateau should correspond to the redox potential of Fe 3+ /Fe 2+ . However, the peak height at 710.0 eV for G Fe is somewhat higher than that for I Fe and those for LiFePO 4 and LiMn y Fe 1− y PO 4 previously reported, suggesting that the reduction of Fe should be incomplete in the LiMn 0.6 Fe 0.4 PO 4 nanowire. The difference spectrum J Fe =G Fe −0.5×A Fe (Figure b) is almost identical to previous Fe L ‐edge XAS results for LiFePO 4 and LiMn 0.5 Fe 0.5 PO 4 , implying that approximately 33 % Fe sites remain as Fe 3+ , whereas the other Fe atoms are reduced to Fe 2+ at 2.8 V.…”

“…Mn [19,[21][22][23][24] suggesting that the reduction of Fe should be incomplete in the LiMn 0.6 Fe 0.4 PO 4 nanowire. The differences pectrum J Fe = G Fe À0.5 A Fe (Figure 2b)i sa lmosti dentical to previous Fe L-edge XAS results for LiFePO 4 [19,21,24] and LiMn 0.5 Fe 0.5 PO 4 , [22] implying that approximately 33 %F es ites remaina sF e 3 + ,w hereas the other Fe atoms are reduced to Fe 2 + at 2.8 V.…”

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

“…The surface‐sensitive total‐electron‐yield (TEY) XAS spectra for a – e are shown in Figure . For a at 4.3 V (charged state), the Fe L 2,3 ‐edge XAS spectrum was ascribed to Fe 3+ high‐spin (HS) state as reported in previous results . As discharging, the XAS spectrum gradually changed.…”

“…For aa t4 .3 V( charged state), the Fe L 2,3 -edge XAS spectrum was ascribed to Fe 3 + high-spin (HS) state as reported in previous results. [11][12][13][14] As discharging, the XAS spectrum gradually changed. The L 3 main peak at 710.0 eV became small.…”