XAFS study of LiCo_1-xFe_xO₂ cathode for rechargeable lithium battery by laboratory XAFS spectrometer

The change of local structure in layered-rock-salt-type iron doped lithium cobaltate LiCo_1-xFe_xO₂ under electrochemical Li de-intercalation (charge) /re-intercalation (discharge) was studied by a laboratory type XAFS spectrometer. In Co K-XANES and Fe K-XANES of LiCo_0.85Fe_0.15O₂ the absorption peak shifted to higher energy by 1.5-2eV for Co K-edge and by 2-2.5eV for Fe K-edge, respectively, after the first charge. The spectra returned close to initial position and had almost original shape after the first discharge. In Co K- and Fe K-EXAFS of LiCo_0.85Fe_0.15O₂ during the first charge and discharge the reversible change of the local structure was observed mainly around the Co atoms although the partly irreversible change of the local structure was found around the Fe atoms. The variation of local structure occurred in similar manner for the samples with x=0.05 and 0.25. This indicates that both Co³⁺/Co⁴⁺ and Fe³⁺/Fe⁴⁺ redox reactions occur reversibly during the first charge and discharge.