The thermodynamics of lithium batteries and their constructing materials determine electrochemical performances (energy density, capacity, open circuit voltage) as well as battery thermal and safety behavior. In this work, the thermodynamics of both spinel-type (lithium manganese oxide-based) and layered oxide-type (Ni-Mn-Co-oxide-based) cathode materials will be discussed. The related multi-component phase diagrams indicate the battery relevant heterogeneous reactions. Various types of calorimetry were used to measure heat capacities, enthalpies of formation and enthalpy increments, respectively. The experimental data were then used for CALPHAD-type modeling of the Li-Mn-O system in “sintered state” and “battery state”, respectively, and prediction of battery behavior in operation.