Density functional theory investigations show that the Li+ ion is stabilized at the center of hexagonal carbon ring with the distance of 1.84 from graphene surface. The potential barrier of Li+ ion diffusion on the graphene surface, about 0.32 eV, is much lower than that of Li+ ion penetrating the carbon ring which is 10.68 eV. When a vacancy of graphene exists, potential barrier about 10.25 eV for Li+ ion penetrating the defect is still high, and the ability of the vacancy to sizing the Li + ion is also observed. Electronic densities of states show that the formation of a localized bond between Li atom and edge carbon of vacancy is the main reason for high potential barrier when Li+ ion penetrate a vacancy. While Coulomb repulsion is the control factor for high potential barrier in case of Li+ ion penetrating a carbon ring. © 2011 Elsevier B.V. All rights reserved.
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