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

Shuttle effect caused by the dissolution and diffusion of lithium polysulfides (Li₂S_n) in electrolytes is the main reason that hinders the application of lithium-sulfur batteries. The introduction of anchoring materials to adsorb Li₂S_n 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 (FeN_x (x = 1, 2, 3, 4)) is conducted to elaborate the anchoring mechanism. We investigate the adsorption of Li₂S_n on FeN_x and study the detailed interaction and electronic structure. It is proved that there is strong interaction between FeN_x and Li₂S_n, which will inhibit the dissolution and diffusion of Li₂S_n (n = 4, 6, 8) and is beneficial to the uniform nucleation of Li₂S and Li₂S₂. In addition, the stability of FeN_x 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 FeN_x improve the performance of lithium-sulfur batteries. It is of guiding significance to the screening and design of anchoring materials in the future.