X-ray absorption fine structure and neutron diffraction analyses of de-intercalation behavior in the LiCoO 2 and LiNiO 2 systems
Abstract
Variations of electronic and local structures of Ni and Co in Li 1 - xNiO 2 and Li 1 - xCoO 2 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 sructure spectra of the Ni K-edge in Li 1 - xNO 2 as a function of x were continuous while an abrupt change was observed for the Co K-edge spectra of Li 1 - xCoO. Radial structure functions obtained by Fourier-transform of the Ni K-edge EXAFS of LiNiO 2 exhibited abnormally low height of the Ni-O peak. This phenomenon is explained by the Jahn—Teller distortion of the NiO 6 octahedron due to the low spin Ni 3+ (d 7) ion. De-intercalation of the Li ion caused oxidation of Ni 3+ (d 7) to Ni 4+ (d 6) and reduced the distortion, hence the Ni-O peak increased with increasing x value. The crystal structures of LiNiO 2 treated with D 2O, and electrochemically de-intercalated Li 0.34NiO 2 were solved by Rietveld analysis of neutron diffraction data.
- Publication:
-
Journal of Power Sources
- Pub Date:
- 1997
- DOI:
- 10.1016/S0378-7753(97)02598-6
- Bibcode:
- 1997JPS....68..536N