Bifunctional Atomically Dispersed Mo-N2/C Nanosheets Boost Lithium Sulfide Deposition/Decomposition for Stable Lithium-Sulfur Batteries.

The sluggish kinetics of lithium polysulfides (LiPS) transformation is recognized as the main obstacle against the practical applications of the lithium-sulfur (Li-S) battery. Inspired by molybdoenzymes in biological catalysis with stable Mo-S bonds, porous Mo-N-C nanosheets with atomically dispersed Mo-N2/C sites are developed as a S cathode to boost the LiPS adsorption and conversion for Li-S batteries. Thanks to its high intrinsic activity and the Mo-N2/C coordination structure, the rate capability and cycling stability of S/Mo-N-C are greatly improved compared with S/N-C due to the accelerated kinetics and suppressed shuttle effect. The S/Mo-N-C delivers a high reversible capacity of 743.9 mAh g-1 at 5 C rate and an extremely low capacity decay rate of 0.018% per cycle after 550 cycles at 2 C rate, outperforming most of the reported cathode materials. Density functional theory calculations suggest that the Mo-N2/C sites can bifunctionally lower the activation energy for Li2S4 to Li2S conversion and the decomposition barrier of Li2S, accounting for its inherently high activity toward LiPS transformation.