By using the H-terminated planar cluster model, C54H18, the stabilization site of a Li+ ion was determined by means of the unrestricted Hartree–Fock AM1 energy gradient method. Six kinds of stabilization site were considered, suggesting that the Li+ ion was quite stable at the 2 distinct sites in the bulk where the potential energy difference between them was 2.0kcal/mol. For the Li+ ions stabilized at these 2 sites, diffusion processes were simulated at 800K via a direct molecular orbital dynamics procedure. No jump diffusion of Li+ ions occurred among the stabilization sites, but they diffused along the outline of the cluster model with fluctuations. It required 2.0ps for a Li+ ion to diffuse from the lower potential site to another equivalent site. On the other hand, it required 0.7ps to move from the higher potential site to the unstable circumference site composed of corner (armchair edge) C atoms. As a result, the diffusivity was some 10-8 to 10-7m2/s.

Diffusion of Li+ Ion in Graphite Cluster Model at 800K - a Direct Molecular Orbital Dynamics Study. A.Shimizu, H.Tachikawa: Journal of Physics and Chemistry of Solids, 2002, 63[4], 619-24