Origin of Deterioration for LiNiO[sub 2] Cathode Material during Storage in Air

Lithium nickel oxide, a potential candidate for cathode material for lithium-ion batteries, showed a distinct deterioration after storage in air for a time. The origin of this deterioration was explored by investigating surface structure, surface species, and ionic oxidation state of fresh and stored materials. Rietveld analysis of X-ray diffraction patterns showed not only the formation of on the surface, but also a weakening of ordered layered structure for the stored materials. X-ray photoelectron spectroscopy revealed that transforms to and active oxygen species exist on the surface of stored materials. Temperature programmed desorption-mass spectroscopy measurements gave evidence that active oxygen species occur on the surface of after storage. A surface reaction mechanism based on the transformation of and the evolution of active oxygen species is proposed.