Electrical conductivity change of AM-GICs by ternarization with ammonia Original Research Article

Electrical conductivity change of alkali metal–graphite intercalation compounds such as MC8 and MC24 (M=K, Rb, Cs) was determined during ternarization with ammonia. The conductivity of MC8 decreased by the ammoniation. A remarkable decrease of the conductivity during initial stage of ammoniation was observed for KC8. The conductivity of RbC8 decreased rather moderately and that of CsC8 was most insensitive to the ammoniation. The energy of interaction of alkali metal ion with ammonia molecule was evaluated by theoretical calculation using density functional theory and obtained the following result: K+–NH3, −28.9 kcal/mol; Rb+–NH3, −24.4 kcal/mol; Cs+–NH3, −19.3 kcal/mol. This result clearly explained the observed difference in the degree of the conductivity decrease of the MC8 compounds against the ammoniation. Thus, the conductivity decrease can be considered to be originated from the interaction of ammonia molecules with alkali metal ions, resulting in the backtransfer of conduction electrons from carbon layers to alkali metal ions. The conductivity change for KC24–NH3 and KC48–NH3 systems was relatively small compared to the system KC8–NH3. This was explained by taking into account the fact that the nanospace of KC24 and KC48 is larger than that of KC8.