The Structure of Lithium Intercalated Graphite Using an Effective Atomic Charge of Lithium

Using the experimental graphene layer spacing of the stage 1 model as a constraint, the effective atomic charge of lithium, δ_Li, in lithium-intercalated graphite (LIG) was determined. In order to confirm that lithium in LIG exists in a partially ionic state, quantum mechanical calculations were also carried out for several lithium-carbon systems. Using a fixed δ_Li, the graphene layer spacing and structures for hexagonal graphite, stage 3, stage 2, and stage 1 models, were obtained. The more lithium is intercalated into the graphite, the wider the layer spacing becomes. The distortion of structures due to lithium intercalation was not observed until the stage 1 model was formed. In stage 1 and stage 2 models, the graphene layers shifted from ABAB to AAAA stacking as lithium was intercalated to the hexagonal graphite. However, the stage 3 model showed a shift of layers from ABABAB to AB′AAB″A stacking, where B′ and B″ represent the graphene layers which have shifted slightly from B. Only the graphene layers that have the intercalated lithium layers between them shifted to AA stacking.