The reaction between LiNiO2 and CO2 is relevant to the synthesis and storage of LiNiO2-based cathode materials for lithium ion batteries. In this work, this reaction was investigated in pure CO2 atmosphere at both room and high temperatures. The reaction products (Li2CO3, NiO, and O2) and activation energies were determined by means of XRD, XPS, MS and TGA techniques. The reaction mechanism was explored in an effort to clarify some inconsistencies in the previous works. Kinetics analysis was also carried out to understand the reaction process relevant to the synthesis and storage of LiNiO2 cathode material.