  In this work, we adopt first-principle calculations based on density
functional theory and Kinetic Monte Carlo simulations to investigate the
adsorption and diffusion of lithium in bilayer graphene (BLG) as anodes in
lithium-ion batteries. Based on energy barriers directly obtained from
first-principle calculations for single-Li and two-Li intercalated BLG, a new
equation was deduced for predicting energy barriers considering Li's
interactions for multi-Li intercalated BLG. Our calculated results indicate
that Li energetically prefers to intercalate within rather than adsorb outside
the bilayer graphene. Additionally, lithium exists in cationic state in the
bilayer graphene. More excitingly, ultrafast Li diffusion coefficient, within
AB-stacked BLG near room temperature was obtained, which reproduces the
ultrafast Li diffusion coefficient measured in recent experiment. However,
ultrafast Li diffusion was not found within AA-stacked BLG near room
temperature. The analyses of potential distribution indicate that the stacking
structure of BLG greatly affects its height of potential well within BLG, which
directly leads to the large difference in Li diffusion. Furthermore, it is
found that both the interaction among Li ions and the stacking, structure cause
Li diffusion within AB-stacked BLG to exhibit directional preference. Finally,
the temperature dependence of Li diffusion is described by the Arrhenius law.
These findings suggest that the stacking structure of BLG has an important
influence on Li diffusion within BLG, and changing the stacking structure of
BLG is one possible way to greatly improve Li diffusion rate within BLG. At
last, it is suggested that AB-stacked BLG can be an excellent candidate for
anode material in Lithium-ion batteries.
