Changes in the crystal structure and transition metal valency in LiFexCo1-xO2 (0 ≤ x ≤ 0.25) positive electrodes during the charge-discharge of Li/LiFexCo1-xO2 cells were examined using ex situ X-ray diffraction measurements, Fe and Co K-X-ray absorption near edge spectroscopy (XANES) and 57Fe Mossbauer spectroscopy. An iron-doped host material with rhombohedral symmetry was obtained up to 25% Fe per formula unit in LiCoO2 by hydrothermal reaction below 300°C from a mixture of Co3+-Fe3+ co-precipitate (iron-doped CoOOH) and LiOH. No symmetry changes were observed during electrochemical charge-discharge tests up to the tenth cycle. The structures of Li-extracted and reinserted samples were determined by a model similar to LiCoO2 prepared at low temperature in which Li ions are located at the interstitial 6c and octahedral 3a sites. 57Fe Mossbauer and Fe and Co K-XANES spectra at 293 K indicated the presence of tetravalent Fe ions upon oxidation up to 4.3 V.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry