DFT study of N,S co-doped graphene anodes for Na-ion storage and diffusion

Abstract

It is known that heteroatom dopants can modify the electrochemical storage performance of anode materials. Here, we performed first-principles calculations to investigate the adsorption and migration of Na atoms on a N,S co-doped graphene anode. By considering various configurations of N,S co-doped graphene structures, we see that the most stable system has N and S dopants in neighboring locations with an N “topological defect” and an S-bulge structure whilst the structure appears semi-metallic with spin polarization. Meanwhile, N,S co-doping not only increases the adsorption energy of Na ions on graphene, but it also increases the inter-layer distance between the graphene sheets and ensures that the Na ion diffusion energy barrier is moderate. Meanwhile, the co-doping of N and S can significantly promote the interaction between higher concentrations of Na atoms and graphene and, more importantly, increases the average Na adsorption energy of the bi-layer structure relative to single-layer N,S co-doped graphene. Thus, the Na ion adsorption capacity of the co-doped graphene system is improved. This work not only highlights the underlying interplay between the dopants in Na-ion storage performance, but also opens up a new avenue for modifying 2D materials with superior capacities and superb rate capabilities for future sodium-ion batteries.