Two-dimensional ordering governs the overpotential of Li intercalation and plating on graphene and its variants

In this work, the Li ordering and its influence on Li intercalation and plating on graphite, bilayer, and single-layer graphene are investigated by first-principles calculation with two-dimensional cluster expansion and van der Waals corrections. The results show that Li intercalation has a multistage feature for graphite and bilayer graphene at Li concentrations from C2 to LiC6. Beyond LiC6, Li atoms are crowded in graphite and bilayer graphene, resulting in a negative discharge voltage. The calculated overpotential indicates Li plating easily happens on graphite but is unlikely on bilayer graphene. For single-layer graphene, Li atoms uniformly cover the graphene surface from C2 to LiC4 with the presence of voltage stages, while forming an atomic island at a higher Li concentration. Our findings not only give a good recount on recent Li plating phenomena in Li-ion batteries but also provide a rationale for circumventing those side reactions on graphene and its variants.