X-ray absorption fine structure and neutron diffraction analyses of de-intercalation behavior in the LiCoO2 and LiNiO2 systems

Variations of electronic and local structures of Ni and Co in Li1-xNiO2 and Li1-xCoO2 as a function of x were clarified for the first time by in situ X-ray absorption fine structure analysis (XAFS), Chemical shifts of the X-ray absorption near edge stucture spectra of the Ni Kedge in Li1-xNO2 as a function of x were continuous while an abrupt change was observed for the Co K-edge spectra of Li1-xCoO. Radial structure functions obtained by Fourier-transform of the Ni K-edge EXAFS of LiNiO2 exhibited abnormal; low height of the Ni-O peak. This phenomenon is explained by the Jahn-Teller distortion of the NiO6 octahedron due to the low spin Ni3+ (d(7)) ion. De-intercalation of the Li ion caused oxidation of Ni3+ (d(7)) to Ni4+ (d(6)) and reduced the distortion, hence the Ni-O peak increased with increasing x value. The crystal structures of LiNiO2 treated with D2O, and electrochemically de-intercalated Li0.34NiO2 were solved by Rietveld analysis of neutron diffraction data. (C) 1997 Elsevier Science S.A.