Achieving a Quasi-Solid-State Conversion of Polysulfides via Building High Efficiency Heterostructure for Room Temperature Na-S Batteries

The practical application of room temperature sodium-sulfur (RT Na-S) batteries are prevented by the sulfur insulation, the severe shuttling effect of high-order sodium polysulfides (Na2Sn, 4 <= n <= 8), and the sluggish reaction kinetics. Therefore, designing an ideal host material to suppress the polysulfides shuttle process and accelerate the redox reactions of soluble NaPSs to Na2S2/Na2S is of paramount importance for RT Na-S batteries. Here, a quasi-solid-state transformation of NaPSs is realized by building high efficiency MoC-W2C heterostructure in freestanding multichannel carbon nanofibers via electrospinning and calcination methods (MoC-W2C-MCNFs). The multichannel carbon nanofibers are interlinked micro-mesoporous structures that can accommodate volume change of electrode materials and confine the entire redox process of NaPSs (restraining the polysulfides shuttle process). Meanwhile, the MoC-W2C heterostructure with abundant heterointerfaces can facilitate electron/ion transport and accelerate conversion of NaPSs. Consequently, the S/MoC-W2C-MCNFs cathode delivers a high capacity of 640 mAh g-1 after 500 cycles at 0.2 A g-1 and an excellent reversible performance of 200 mAh g-1 after ultralong 3500 cycles at 4 A g-1. What's more, the heterostructure catalytic mechanism (a quasi-solid-state transformation) is proposed and confirmed in carbonate electrolyte by combining experimentally and theoretically. The MoC-W2C heterostructures embedded in freestanding multichannel carbon nanofibers prepared by simple electrospinning technique conveys superior performance when used as free-standing paper anode of room-temperature sodium-sulfur batteries. Meanwhile, a quasi-solid-state transformation mechanism is proposed and confirmed by combining experimentally and theoretically. image