Resonant photoemission spectroscopy of the cathode material Li_xMn_(0.5)Fe_(0.5)PO_4 for lithiurn-ion battery

摘要

We have investigated the change in the electronic structure of Li_xMn_(0.5)Fe_(0.5)PO_4 through the charge process, especially in the transition metal partial DOS using X-ray absorption and resonant photoemission spectroscopy measurements. The oxidation reaction between Fe~(2+) and Fe~(3+) proceeds while the 0.5 Li ions are extracted from LiMno.5Feo.5PO4. Moreover, comparing resonant photoemission spectra of Li_xMn_(0.5)Fe_(0.5)PO_4 with those of Li_xFePO_4, we have found that both spectral line-shapes are almost identical, suggesting that the strong localization of the Fe 3d states in the Li_xMn_(0.5)Fe_(0.5)PO_4 system. On the other hand, in Mn 2p-3d X-ray absorption and resonant photoemission spectra, the Mn oxidation reaction from Mn~(2+) to Mn~(3+) partially occurs and Mn 3d states of Li_xMn_(0.5)Fe_(0.5)PO_4 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 Fe~(3+) 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.