X-ray absorption near edge structure study on valence changes of Ni and Co in Li1-xNi0.82Co0.15M0.03O2 (M=Nb, Ti) cathode materials

X-ray absorption near edge (XANES) measurements at K-edges of Ni and Co were carried out on the Li deintercalated Li1-xNi0.82Co0.15M0.03O2 (M=Nb, Ti) cathode materials for Li secondary batteries. Samples were prepared by two different ways of Li deintercalation. One was cathode materials removed from the coin cell charged in the different degree of Li deintercalation and the other was chemically processed with hydrochloric acid in the aqueous solution. Comparisons of XANES spectra between LNCO and Ti or Nb doped LNCO were made, and it was found that the formation of Ni4+ was greatly reduced in the charged cathode materials with the dope of Ti or Nb. The similar results were obtained within samples prepared by the real charge and the chemical charge. Valence of Co was invariable during the charge, and was supposed to be trivalent. (author)