SnS 2 -functionalized separator for stable room-temperature sodium-sulfur batteries

Abstract Despite their potential, the practical commercialization of room-temperature sodium-sulfur (RT-Na-S) batteries is hindered by poor sulfur conversion rates and the persistent shuttling of soluble polysulfides. In the present work, sheet-like SnS 2 was synthesized by a solvothermal route and vacuum-filtered onto both sides of Celgard 2500 to build a separator coating with a mass loading of about 0.2 mg/cm 2 . The electrochemical behavior of the SnS 2 -functionalized separator was investigated using ACC@S cathodes with a sulfur loading of around 1 mg/cm 2 through Na 2 S 6 adsorption, cyclic voltammetry (CV), rate testing, and long-term cycling. The Na 2 S 6 solution becomes obviously decolorized after contacting SnS 2 , confirming strong polysulfide affinity. Selected CV profiles recorded between 0.1 and 0.5 mV/s demonstrate increasing peak currents alongside highly consistent redox behaviors, indicating reversible sulfur chemistry with acceptable polarization. Under a low current density of 0.1 C, the cell delivers a specific capacity of 1228.5 mAh/g at the third cycle, maintaining 772.1 mAh/g following 200 continuous cycles. Furthermore, rate performance evaluated between 0.1 and 2.0 C demonstrate mean capacities of 1227.6, 1087.4, 937.8, 781.2, and 570.6 mAh/g, respectively. Notably, decreasing the C-rate back to 0.1 C yields a recovered high capacity of 1142.5 mAh/g. After 1000 cycles, when operated under a current density of 1 C, the cell successfully retains a stable capacity of 214.2 mAh/g. These results show that SnS 2 -functionalized separators are a promising route for regulating the polysulfide behavior of RT-Na-S batteries.