The reaction of CO2 and practical high-performance cathode materials LiNi1-x-yCoxAlyO2 was examined with XRD at RT and high temperature, TGA, IR, and chemical analysis. Even at room temperature, Li deintercalation took place and formed Li2CO3 on the mother surface. The conversion to Li2CO3 in air at 55% RH at 25 degrees C was in proportion to the square root of exposure time. It was 8% after being left for 500 h. Using high-temperature XRD at 25-800 degrees C, the Li2CO3-phase formation was confirmed from about 500 degrees C, and the conversion exceeded 70% under atmospheric CO, at 675 degrees C, The activation energy of the reaction of deintercalated Li and CO2 was estimated by Ozawa＇s method. The activation energy obtained using Ozawa＇s method was 130 kJ/mol for CO2 diffusing through the Li2CO3 layer which formed on the surface during the reaction.