Theoretical phase diagram for Li-intercalated graphite

A mean-field model for the phase diagram of Li-intercalated graphite is presented. Recent observations indicate that different Li graphite compounds occur with the same stage but with different, nearly commensurate in-plane Li densities. This phenomenon, which is a consequence of the corrugation potential of the host graphite lattice, is accounted for approximately in the present model by a small modification of the effective in-plane alkali-alkali potential. The resulting calculated phase diagram agrees well with experiment. The stability of the dilute stage-two phase is identified as a consequence of the high entropy of the compound. The dense stage-two compound has low entropy and decomposes at much lower temperature. A comparison of the present model with previous models is given, and the extension to other alkali-metal compounds is considered.