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

Abstract 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.