Resonant photoemission spectroscopy of the cathode material Li _xMn_0.5Fe_0.5PO₄ for lithium-ion battery

We have investigated the change in the electronic structure of Li _xMn_0.5Fe_0.5PO₄ through the charge process, especially in the transition metal partial DOS using X-ray absorption and resonant photoemission spectroscopy measurements. The oxidation reaction between Fe²⁺ and Fe³⁺ proceeds while the 0.5 Li ions are extracted from LiMn_0.5Fe_0.5PO₄. Moreover, comparing resonant photoemission spectra of Li_xMn _0.5Fe_0.5PO₄ with those of Li _xFePO₄, we have found that both spectral line-shapes are almost identical, suggesting that the strong localization of the Fe 3d states in the LiMn_0.5Fe_0.5PO₄ system. On the other hand, in Mn 2p-3d X-ray absorption and resonant photoemission spectra, the Mn oxidation reaction from Mn²⁺ to Mn³⁺ partially occurs and Mn 3d states of Li_xMn_0.5Fe_0.5PO₄ remain almost unchanged through the charge reaction. Reflecting the difference in the strength of the interaction between the transition metal Fe or Mn ions and the oxygen ions, it is suggested that although the oxidation from Fe ²⁺ to Fe³⁺ proceeds largely on Fe ions during the charge reaction from x = 1.0 to 0.5, the charge compensation for the electron exchange mainly occurs not only at the Mn ions but also at the poly-anion sites during the charge reaction from x = 0.5 to 0.