Encapsulating Co₉S₈ nanocrystals into CNT-reinforced N-doped carbon nanofibers as a chainmail-like electrocatalyst for advanced Li-S batteries with high sulfur loading

Li-S batteries have been regarded as one promising candidate for next-generation energy storage systems, however, their practical implementations are severely hindered by the intractable polysulfides shuttle (PSS) effect and retarded conversion kinetics. Herein, a flexible electrode consisting of Co₉S₈ nanocrystals and CNTs encapsulated inside porous N-doped carbon nanofibers (NCF) (CNT@NC/Co₉S₈) was developed by electrospinning followed by in-situ sulfurization. The carbon nanofibers and embedded CNTs build a highly conductive network, while the Co₉S₈ and N dopant provide more polar sites for LiPSs confinement. This self-supported flexible electrode with a sulfur loading of 12.5 mg cm⁻² exhibits a high initial discharge capacity (1207.7 mAh g⁻¹ at 0.1C), excellent rate capability (831.2 mAh g⁻¹ at 4.0C) and cycling stability (765.5 mAh g⁻¹ with a capacity retention of 78.1% after 1000 cycles at 2.0C). Moreover, when the sulfur loading increases to 20 and 30 mg cm⁻², high capacities of 869.2 and 706.6 mAh g⁻¹can still be obtained at 0.1C after 100 cycles, respectively. Theoretical analysis suggests that the sulfur cathode built on CNT@NC/Co₉S₈ is electrocatalytically active towards LiPSs redox with enhanced conversion dynamics, thus mitigating the detrimental PSS effect.