High resolution x-ray absorption and emission spectroscopy of LixCoO2 single crystals as a function delithiation

The effect of delithiation in LixCoO2 is studied by high resolution Co K-edge x-ray absorption and x-ray emission spectroscopy. Polarization dependence of the x-ray absorption spectra on single crystal samples is exploited to reveal information on the anisotropic electronic structure. We find that the electronic structure of LixCoO2 is significantly affected by delithiation in which the Co ions oxidation state tending to change from 3+ to 4+. The Co intersite (intrasite) 4p–3d hybridization suffers a decrease (increase) by delithiation. The unoccupied 3d t2g orbitals with a1g symmetry, containing substantial O 2p character, hybridize isotropically with Co 4p orbitals and likely to have itinerant character unlike anisotropically hybridized 3d eg orbitals. Such a peculiar electronic structure could have significant effect on the mobility of Li in LixCoO2 cathode and hence the battery characteristics.