In the present work, we have studied the layered O3 and O2 structural LiCoO2–CoO2 pseudo-binary systems using the CALPHAD approach. In the O3 structural LiCoO2–CoO2 system, the O3-LiCoO2 phase is modeled based on the available thermodynamic information, especially the heat capacity data. The parameters of other phases, i.e. O3′ (ordered O3), H1-3 and O1, are accordingly adjusted based on the experimental and ab initio data. The whole system is then reassessed. In the O2 structural LiCoO2–CoO2 system, the O2-LiCoO2 phase is modeled based on the enthalpy difference from the O3-LiCoO2 phase. Other phases, i.e. O2′ (ordered O2), T#2, T#2′ (ordered T#2) and O6, are correspondingly described using appropriate sublattice models. The parameters for each phase are adjusted considering both the experimental and ab initio data. The thermodynamic calculations agree well with literature. Measured Li/LiCoO2 cell voltages were used to support the modeling and are well reproduced by the thermodynamic description.