A new method for the synthesis of GICs using LiCl-KCl molten salts has been reported recently . This method has led to a series of investigations on pure single-phase bulk GICs that were difficult to synthesize using other methods such as electrochemical intercalation, solid-vapor method, and lithium-based molten alloy method. According to the mechanism proposed for the Li-based molten alloy and LiCl-KCl molten salt methods, the intercalation of Li occurs first to form LiC6, followed by the complete replacement of Li by other elements . In this mechanism, the GIC with the objective element inserted following Li (or K) should be at least more energetically stable than the Li-GIC (or K-GIC). However, only a few studies have quantitatively discussed the stability of GICs with various elements. Hence, understanding the formation energies of the GICs and their mechanism is essential.