Mechanism of Li storage on graphene nanoflakes: Density functional theory study

Abstract

The efficiency of metal storage in carbon materials directly affects battery performance. Therefore, elucidating the storage mechanism is important for developing high-efficiency and new storage materials. In this study, interatomic interactions between Li species (Li atoms and Li+ ions) and graphene nanoflakes (GRs) have been investigated using the density functional theory method to elucidate the mechanism of Li storage on GRs. Moreover, single, double, and triple Li species were examined. For single Li systems (n = 1), the binding energy and diffusion barrier of Li on GRs were investigated, while the interatomic interactions and packing structures of Li species on GRs were investigated for double and triple Li systems (n = 2 and 3, respectively). The diffusion barriers for Li+ and Li for n = 1 were calculated to be 5.90 and 6.84 kcal/mol, respectively. For n = 2, the diffusion was strongly affected by the counter Li species and was attributed to the repulsive interactions. For n = 2, the close packing configurations of Li species on the surface of the GRs consisted of biphenyl structures where Li species were located inside the benzene rings of the biphenyl-like site of GRs. For n = 3, three Li species were bound to the triphenylene sites (two biphenyl-like sites). The electronic states of the Li species stored on GRs were discussed using the theoretical results.