Study of the Jahn-Teller distortion in LiNiO2, a cathode material in a rechargeable lithium battery, by in situ X-ray absorption fine structure analysis

Structural changes accompanying the electrochemical Li deintercalation of Li1-xNiO2 and Li1-xCoO2 were studied by the transmission X-ray absorption fine structure (XAFS) technique using an in situ X-ray cell of original design. Our results revealed that the Jahn-Teller distortion of the Ni-O octahedra found in LiNiO2 decreased as the Li ion was removed from the cathode. The observed X-ray absorption near-edge structures (XANES) of Li1-xNiO2 and Li1-xCoO2 as a function of x are consistent with the phase transitions found by powder-diffraction studies. The Ni-O, Co-O, and Ni-Ni interatomic distances decreased almost linearly as the Li content decreased to x = 0.8, while the Co-Co distance slightly decreased to x = 0.5 and increased up to x = 0.8, The local distortion of NiO6 octahedra also decrease with increasing y in a Li(Ni1-y, Co-y)O-2 solid solution. (C) 1998 Academic Press.