A theoretical study of the NbS monolayer as a promising anchoring material for lithium-sulfur batteries.

Developing efficient cathode materials with good conductivity to restrain the shuttle effect and promote the reaction kinetics has been a key scientific issue for the development of lithium-sulfur (Li-S) batteries. Here, by means of first-principles computations, we demonstrate that the NbS monolayer is a promising cathode anchoring material for Li-S batteries. It has a metallic feature that improves the conductivity of sulfur and lithium polysulfides (LiPSs) and promotes the electron transfer ability. The discharge products LiPSs are strongly anchored on the NbS monolayer without structural distortion, which effectively alleviates the shuttle effect. Remarkably, the reductions of sulfur to soluble LiPSs are spontaneous exothermic reactions while the subsequent reductions to insoluble LiPSs are endothermic reactions with low Gibbs free energy barriers (0.09-0.18 eV) and reaction activation barriers (0.83-0.93 eV), ensuring the rapid discharge process. In addition, the barriers of LiS decomposition and Li atom diffusion are only 0.64 and 0.18 eV, respectively, which improve the reaction kinetics in the charging process and the cycling life of batteries. These results suggest that the NbS monolayer can be utilized as a promising anchoring material for Li-S batteries to achieve high reversible capacity and conversion efficiency.