Accelerating Sulfur Conversion Kinetics via CoS2-MgS Heterostructure for Lithium Sulfur Batteries

The ultra-high theoretical specific capacity of sulfur (1672 mAh g-1) has attracted researchers to intensely explore lithium-sulfur batteries. However, the shuttle effect of polysulfides and the slow conversion kinetics of sulfur have hindered its advancement. Herein, we synthesized CoS2-MgS heterostructure catalysts deposited on acetylene black nanoparticles, which were used as separator coatings to improve lithium-sulfur battery performance. Various experiments, such as XPS, Tafel curves, Li2S6 symmetric cells, Li2S deposition, and DFT calculations, identified the advantages of the CoS2-MgS heterostructure: rapid polar adsorption of CoS2 to polysulfides through oxidized partial Co2+ to Co3+ and fast lithium-ion migration in MgS. The coin cells delivered an initial discharge capacity of 573.4 mAh g-1 and cycled stably for 600 cycles at 5 C with a capacity decay rate of 0.08% per cycle; The battery retained a specific capacity of 545.5 mAh g-1 (4.3 mAh cm-2) after 100 cycles at 0.1 C with a sulfur loading of 7.87 mg cm-2. In addition, laminated pouch cells with a sulfur of 311.5 mg exhibited excellent cycle stability, maintaining 768.3 mAh g-1 (239 mAh) after 80 cycles. This work provides ideas to find novel composites that have both fast lithium-ion migration and strong polar adsorption for sulfur conversion while providing a reference for pouch battery research.