Single-atom Fe and N co-doped graphene for lithium-sulfur batteries: a density functional theory study

Abstract

Shuttle effect caused by the dissolution and diffusion of lithium polysulfides (Li2Sn) in electrolytes is the main reason that hinders the application of lithium-sulfur batteries. The introduction of anchoring materials to adsorb Li2Sn is an effective way to overcome this problem and achieve long-term cycling stability. In this work, a systematical density functional theory study of single-atom Fe and N co-doped graphene (FeNx (x = 1, 2, 3, 4)) is conducted to elaborate the anchoring mechanism. We investigate the adsorption of Li2Sn on FeNx and study the detailed interaction and electronic structure. It is proved that there is strong interaction between FeNx and Li2Sn, which will inhibit the dissolution and diffusion of Li2Sn (n = 4, 6, 8) and is beneficial to the uniform nucleation of Li2S and Li2S2. In addition, the stability of FeNx can be improved by increasing the number of N coordination. Finally, the adsorption energy can be adjusted by doping concentration of atoms. Hence, our work reveals in detail the mechanism how FeNx improve the performance of lithium-sulfur batteries. It is of guiding significance to the screening and design of anchoring materials in the future.