The CoFeNC@NC Catalyst with Numerous Surface Cracks Bidirectionally Catalyzes the Conversion of Polysulfides to Accelerate the Reaction Kinetics of Lithium–Sulfur Batteries

More and more attention has been paid to lithium–sulfur (Li─S) batteries due to their high energy density and low cost. However, the intractable “shuttle effect” and the low conductivity of S and its reaction product, Li2S, compromise battery performance. To address the inherent challenges, a hollow composite catalyst as a separator coating material is designed, in which CoFe alloy is embedded in a carbon skeleton (CoFeNC@NC). In the hybrid structure, the carbon layer can endow the batteries with high electrical conductivity, while the CoFe alloy can effectively bidirectionally catalyze the conversion between lithium polysulfides (LiPSs) and Li2S, accelerating the reaction kinetics and reducing the dissolution of LiPSs. Furthermore, the distinctive hollow structure with a cracked surface can facilitate the exposure of a more accessible catalytically active site and enhance Li+ diffusion. Benefiting from the synergistic effects, Li─S batteries with a CoFeNC@NC catalyst achieve a high sulfur utilization (1250.8 mAh g−1 at 0.2 C), superior rate performance (756 mAh g−1 at 2 C), and excellent cycling stability (an ultralow capacity fading of 0.054% per cycle at 1 C for 1000 cycles). Even at a sulfur loading of 5.3 mg cm−2, a high area capacity of 4.05 mAh cm−2 can still be achieved after 100 cycles, demonstrating its potential practicality. The CoFeNC@NC complex is composed of CoFe alloy and highly conductive carbon material, with multiple functions that enhance the conductivity of lithium–sulfur batteries while also effectively adsorbing lithium polysulfides and facilitating their rapid conversion. Furthermore, the unique hollow structure with abundant surface cracks ensures effective interaction between the CoFe alloy and lithium polysulfide.