Duplex core-shell Co@Co9S8@NSC nanocrystals for high-performance lithium-sulfur battery through synergistic capture-catalysis-conversion of polysulfide

The slow redox kinetics and shuttle effect of polysulfides are primary challenges that hinder the further application of lithium-sulfur batteries (LSBs) due to the poor conductivity of sulfur and low sulfur utilization. Separator modification through synergistic capture-catalysis-conversion of polysulfides proves to be an effective approach to address these challenges. In this paper, we successfully design and prepare double shell core-shell Co@Co 9 S 8 @NSC nanocrystals encapsulated in sulfur- and nitrogen-co-doped carbon nanotubes (Co@Co 9 S 8 @NSC) as a separator modifier for LSBs. The modified layer (Co@Co 9 S 8 @NSC//PP) exhibits excellent adsorption-catalytic properties, effectively immobilizing soluble lithium polysulfides (LiPSs) and promoting their electrochemical conversion, thereby enhancing lithium ion (Li + ) transport and facilitating a homogeneous lithium deposition process. When we utilize the Co@Co 9 S 8 core-shell structure to coat the polypropylene (PP) separator, the results demonstrate that the modified separator achieves a high reversible capacity of 591 mAh g −1 after 500 cycles at 1 C and reaches a reversible capacity of 442 mAh g −1 after 1000 cycles at 2 C, accompanied by a low capacity decay rate of only 0.05 % per cycle. The Li/Li symmetric batteries, which have Co@Co 9 S 8 @NSC-coated separators, exhibit long lifetimes exceeding 800 h at current densities of 2 mA cm −2 and 2 mAh cm −2 , along with a low voltage hysteresis of approximately 55 mV. This provides enhanced lithium stripping/plating stability compared to Li/Li symmetric batteries with pure PP separators. This study presents a novel approach to interlayer construction to achieve high sulfur utilization in long-life LSBs by accelerating the redox kinetics of LiPS and mitigating the shuttle effect.