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

Abstract

AbstractMore 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.