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.