A direct molecular orbital method was applied to diffusion of a Li+ ion on a fluorinated graphene surface. A graphene sheet composed of C96F24 was used to model the surface. The total energy and energy gradient on the full dimensional potential energy surface of the Li+C96F24 system were calculated at each time step in the trajectory calculation. The simulation temperatures were between 200 and 1000K. Below 200K, no diffusion of lithium ions occurred and the ion vibrated around an equilibrium point. At about 300K, the lithium ion diffused freely on the surface but did not approach the edge region of the surface. This was due to repulsive interaction with a positively charged carbon atom connected to the fluorine atom, where the bond was polarized as Cδ+-Fδ-. The repulsive interaction strongly dominated the diffusion path of the Li+ ion on the fluorinated graphene. The order of magnitude of the diffusion coefficient for a Li+ ion moving on the fluorinated graphene surface was close to that for a normal graphene surface. At higher temperatures, the Li+ ion moved freely on the fluorinated graphene.

A Direct Molecular Orbital-Molecular Dynamics Study on the Diffusion of the Li Ion on a Fluorinated Graphene Surface. Tachikawa, H.: Journal of Physical Chemistry C, 2008, 112[27], 10193-9