Co<sub>4</sub>S<sub>3</sub>/Co<sub>9</sub>S<sub>8</sub>@rGO as catalyst to enhance the redox kinetics of polysulfide conversion for Li−S batteries

The diligent design and engineering of catalytic conversion catalysts for lithium polysulfides (LiPSs) are considered as a crucial strategy to suppress the migration of high soluble long-chain LiPSs and enhance the electrochemical reaction kinetics of LiPSs. In this work, we developed heterostructured Co4S3/Co9S8 with nano-size structure on reduced graphene oxide (Co4S3/Co9S8@rGO) through a simple hydrothermal method and thermal treatment. Benefiting from its high conductivity and abundant reaction sites, the Co4S3/Co9S8@rGO heterostructure exhibits superior LiPSs adsorption capabilities (particularly for Li2S4 and Li2S2 species), high redox kinetics and enhanced Li2S nucleation dynamics. The results of the lithium ions diffusion coefficients (DLi+) and the Tafel plots tests of S@Co4S3/Co9S8@rGO electrode with Co4S3/Co9S8@rGO interlayer confirmed the faster Li+/e− transfer properties, occurring at the electrode/electrolyte interfaces. Facilitating electron transport and high-catalytic-activity, the S@Co4S3/Co9S8@rGO cathode with interlayer exhibits a high capacity of 1346.13 mAh·g−1 at 0.1C and demonstrates exceptional durability through over 1000 cycles at 2C with a capacity decay of 0.038% per cycle. At a high sulfur loading of 2.99 mg·cm−2, the electrode still delivered a high initial discharge capacity 1168.16 mAh·g−1 and even under lean electrolyte (E/S: 4 μL·mg−1), the electrodes still demonstrate a high discharge capacity of 843.31 mAh·g−1 at 0.2C (2.83 mg·cm−2).