Information about the thermodynamic stability of LiC 6 in the literature is ambiguous at present. The thermodynamic stability of LiC 6 and Li 2 C 2 is investigated by an approach combining differential scanning calorimetry (DSC), X-ray diffraction (XRD) and long-time annealing experiments. It is found that LiC 6 is thermodynamically unstable above 330°C, where in the corresponding composition range Li 2 C 2 and graphite are in thermodynamic equilibrium. During heating, a de-intercalation process is observed in LiC 6 , and eventually a transformation to Li 2 C 2 and graphite. The enthalpy of formation of LiC 6 is below zero as it forms from the pure components, the limits of the enthalpy of formation are set by the tangents to the enthalpies of formation of Li 2 C 2 and graphite. An order–disorder transition in LiC 6 was not observed.