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

Abstract 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 0.1 C), excellent rate capability (831.2 mAh g-1 at 4.0 C) and cycling stability (765.5 mAh g-1 with a capacity retention of 78.1 % after 1000 cycles at 2.0 C). Moreover, when the sulfur loading increases to 20 and 30 mg cm-2, high capacities of 869.2 and 706.6 mAh g-1 can still be obtained at 0.1 C 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.