Tin sulfide modified separator as an efficient polysulfide trapper for stable cycling performance in Li-S batteries

Lithium-sulfur batteries (Li-S) are considered the most promising systems for next-generation energy storage devices due to their high theoretical energy density and relatively low cost. However, the practical applications of Li-S batteries are hindered by the poor electronic conductivity of sulfur and capacity degradation resulting from the shuttle effect of lithium polysulfides (LiPSs). Herein, we demonstrate use of a tin-sulfide (SnS₂) modified separator to facilitate the redox reaction involving LiPS intermediates and realize improved electrochemical performance in a Li-S battery. Density functional theory (DFT) calculations revealed that SnS₂ exhibits a strong affinity with LiPSs and induces a rapid conversion of trapped polysulfides. As a result, Li-S batteries with a SnS₂-modified separator exhibited an enhanced specific capacity of 1300 mA h g^-1 at 0.2C (corresponding to a high areal capacity of 4.03 mA h cm^-2), which was maintained at 1040 mA h g^-1 after 150 cycles. Furthermore, an excellent rate capability is achieved with a capacity of 700 mA h g^-1 (2.17 mA h cm^-2) at 5C. Additionally, the modified separator exhibited excellent cycling performance up to 500 cycles at 2C, with a low capacity decay rate of 0.0710% per cycle. The excellent performance of the sulfur electrode is mainly attributed to the incorporation of the SnS₂ coating layer on the separator, which effectively confines polysulfides via both chemical and physical interaction and rapidly improves lithium ion diffusion. Moreover, the SnS₂ coating layer greatly improves sulfur utilization and efficiently accelerates the kinetic conversion of trapped polysulfides.