Monte Carlo simulation was used to investigate the variation of the chemical diffusion coefficient of Li ions in graphite as a function of applied voltage and its relationship to the staging phenomenon. The interatomic potential between Li ions was parameterized using density functional theory and molecular statics to include interactions between Li ions through host-material elastic deformation. The present simulation of bulk graphite could simulate Li ion migration without the uncertainties encountered in some experiments, and reproduced well not only the √3 x √3 in-plane superlattice and stage structures observed in experiments, but also the decrease in chemical diffusion coefficient when two phases coexisted; reflecting the decrease in the thermodynamic factor. It was clearly shown that the stage structure and decrease in the chemical diffusion coefficient could be explained simply in terms of interactions between Li ions via deformation of the host material. Sub-stages between stages 1 and 2 were found which could cause further uncertainties in observations of the diffusion coefficient in experiments.

A Monte Carlo Study of Host-Material Deformation Effect on Li Migration in Graphite. R.Kobayashi, N.Ohba, T.Tamura, S.Ogata: Journal of the Physical Society of Japan, 2013, 82[9], 094603