The stability of the lithium ion battery (LIB) using LiCoO2 as a cathode material in charging/discharging process was investigated on the basis of the first-principles density functional theory calculations. The voltage curve obtained by total electronic energy reproduced the trend of the experimental data such as the instability of the battery at the charged state. Mulliken's population analysis (MPA) and energy density analysis (EDA) techniques were utilized to estimate the partial charge and partial energy in LixCoO2 species. During charging/discharging, Mulliken charge of oxygen changes and, therefore, its local energy varies. On the other hand, the local energy of cobalt drastically changes at low lithium content, whereas its Mulliken charge approximately remains constant. The present results indicate that the local analysis is essential to clarify the origin of the stability of LIB. (C) 2013 The Electrochemical Society.