Abstract:

Based on density functional theory (DFT) with the dispersion correction method, the formation energies, charge transfer, cell potential, and migration process for Na storage in bilayer graphene (BLG) with double vacancy (DV) defects were studied. The formation energy results indicate that one Na atom adsorption or intercalation on or into the center of the vacancy is more favorable. The charge density distribution and Bader charge results indicate that the interactions between Na atoms and BLG are ionic. During Na intercalation in DV defective BLG, the transformation from AB to AA stacking may be delayed as the defect density is increased, and the stable capacity increases to 262.75 mAh·g^-1 (Na:C mole ratio=2:17) for Na adsorption on the surface and intercalation into the interlayer of BLG with DV defects. With increasing Na concentration, Na atoms on the surface tend to aggregate into clusters and eventually macroscopic dendrites. The diffusion energy barrier is increased for adsorbed Na on the surface migrating toward the center of DV defects, while that for the reverse direction is decreased by the intercalated Na atoms, which enhances the storage of Na on the surface of BLG with DV defects.

Key words: Bilayer graphene, Defect, Capacity, Density function theory, Diffusion