XAFS characterization of Li deintercalation in rechargeable lithium battery materials, LiCoO2-LiNiO2

In situ measurements of the Ni and Co K-edge XAFS spectra of Li1-xNiO2 and Li1-xCoO2 as a function of x were successfully carried out for the first time using an electrochemical cell. It is observed that a local Jahn-Teller distortion of the NiO6 octahedron in LiNiO2 was reduced with deintercalation of Li which caused oxidation of the Jahn-Teller d(7) Ni3+ ion to d(9) Ni4+ ion. A substitution of Co for Ni in LiNiO2 also reduced the local distortion of the NiO6 octahedron. XANES spectra of LiNiO2 shifted to higher energy side with increasing x while an abrupt shape change was observed in the XANES spectra of Li1-xCoO2 corresponding to phase transition.