Effect of Nitrogen Doping on the Li-Storage Capacity of Graphene Nanomaterials

Abstract

We performed first-principles calculations based on density functional theory (DFT) to investigate the adsorption of Li and Na on various kinds of N-doped defect structures in graphene, including monovacancy (MV), divacancy (DV), and Stone–Wales (SW) defects with different amount of graphitic and pyridinic N atoms. Our calculated results first indicate that introducing N-dopants in graphene can effectively reduce the formation energy of defects and in turn increase the probability to generate N-doped defects in graphene. Besides, the formation energy of MV becomes lower than that of DVs when doped with nitrogen, implying that the number of N-doped MV could be more than that of N-doped DVs in N-doped defective graphene. The calculated reversible Li-storage capacity of N-doped defects was shown to gradually decrease with increasing N-dopants in graphene, implying that aggregating many N-dopants in defect sites cannot enhance the reversible Li-storage capacity but may even lower than that of intrinsic defects. Although the inclusion of N-dopants into the intrinsic defects can lower down the Li-storage capacity, the migration energy barrier of defect structures was found to be lifted when N-dopants were introduced, which can suppress the capacity loss induced by vacancy aggregation in graphene.