Accelerating sulfur conversion kinetics via CoS2–MgS heterostructure for lithium sulfur batteries†

The ultra-high theoretical specific capacity of sulfur (1672 mA h 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 the performance of lithium–sulfur batteries. 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 partial oxidation of Co²⁺ to Co³⁺ and fast lithium-ion migration in MgS. The coin cells delivered an initial discharge capacity of 573.4 mA h g⁻¹ and cycled stably for 600 cycles at 5C with a capacity decay rate of 0.08% per cycle. The battery retained a specific capacity of 545.5 mA h g⁻¹ (4.3 mA h cm⁻²) after 100 cycles at 0.1C with a sulfur loading of 7.87 mg cm⁻². In addition, laminated pouch cells with a sulfur content of 311.5 mg exhibited excellent cycle stability, maintaining 768.3 mA h g⁻¹ (239 mA h) after 80 cycles. This work provides ideas for finding novel composites that have both fast lithium-ion migration and strong polar adsorption for sulfur conversion while providing a reference for pouch battery research.