Synergistic effect of Co3Fe7 alloy and N-doped hollow carbon spheres with high activity and stability for high-performance lithium-sulfur batteries

Abstract Lithium-sulfur (Li-S) batteries have attracted extensive attention as a promising next-generation electrochemical energy storage technology, owing to their high energy density and low material cost. However, issues such as severe polarization and poor cycle stability caused by shuttle effect and slow sulfur redox kinetics limit their practical applications. Here, Co3Fe7 alloy embedded into nitrogen-doped hollow carbon sphere composite (CoFe/NHCS) was synthesized as an electrocatalyst for Li-S batteries. The Co3Fe7 alloy demonstrates a strong chemisorption and superior electrocatalytic conversion towards polysulfides, while the nitrogen-doped carbon hollow spheres promote Li+/electron transfer and physically suppress polysulfides shuttling. Their synergistic effect therefore could both accelerate the polysulfides redox conversion and inhibit the polysulfides loss. As a consequence, the Li-S batteries assembled with CoFe/NHCS-modified separators exhibit a superior rate capacity (1029 mAh/g at 2 C) and excellent cycling stability (644 mAh/g at 1 C after 500 cycles). Furthermore, even at a high sulfur loading of 6.7 mg/cm2, a high areal capacity of 5.58 mAh/g is achieved, which is retained at 4.45 mAh/cm2 after 100 cycles. In addition, the CoFe/NHCS possesses an excellent stability in both physical structures and chemical properties over extended cycles, demonstrating its great potential for high-performance and long-cycle-life Li-S batteries.