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[18p-432-7] Electronic States in Oxidized Na_xCoO₂ by X-ray Absorption Spectroscopy Coupled with ab initio Calculation

〇Hideharu Niwa^1,2,3, Kazuyuki Higashiyama^1,2, Kaoru Amaha¹, Wataru Kobayashi^1,2,3, Yutaka Moritomo^1,2,3 (1.Grad. Sch. Pure and Appl. Sci., Univ. Tsukuba, 2.Fac. Pure and Appl. Sci., Univ. Tsukuba, 3.TREMS, Univ. Tsukuba)

Keywords:Sodium-ion secondary battery, soft x-ray absorption spectroscopy

Layered cobalt oxides are promising cathode materials for sodium ion secondary batteries. By combined study of the X-ray absorption spectroscopy around the O K-edge and ab initio calculation, we investigated the electronic state of the Na_xCoO₂ with different oxidization state, i.e, in O3-Na_0.91CoO₂ (CoO₂^-0.91) and P2-Na_0.66CoO₂ (CoO₂^-0.66). The O K-edge spectra in the pre-edge (529 - 536 eV) region shows significant change with oxidization of Na_xCoO₂. These spectral changes are qualitatively reproduced by the calculated partial density of states (pDOSs) of O3-NaCoO₂ and P2-Na_1/2CoO₂. These results indicate that the electrons are partially removed from the O 2p state with oxidization of Na_xCoO₂.