双空位缺陷双层石墨烯储钠性能的第一性原理研究

First-Principles Study of Na Storage in Bilayer Graphene with Double Vacancy Defects

采用基于密度泛函理论(DFT)的色散修正方法,研究了Na吸附和嵌入在双空位缺陷(DV)双层石墨烯(BLG)体系中的形成能、电荷转移、电极电势和扩散行为。形成能计算表明,无论单个Na原子在BLG表面吸附还是层间嵌入,均在DV空位中心处更稳定。电荷密度分布和Bader电荷计算表明Na与BLG的结合方式表现出离子性。Na嵌入DV缺陷BLG层间,缺陷浓度增加使BLG由AB堆垛向AA堆垛转变过程推迟;使Na在DV缺陷BLG的表面和层间能够稳定储钠的容量之和增至262.75 mAh?g^(-1),对应浓度Na与C摩尔比为2:17,储钠浓度继续增加,Na在BLG表面吸附容易产生枝晶或团簇。当层间嵌入Na原子时,表面Na原子向DV缺陷中心方向扩散能垒减小、表面Na原子沿相反方向的扩散能垒增加,DV缺陷的存在提高了BLG表面捕获Na的能力。

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.