Nano-flower spherical SnS2 combined with a special lithium storage mechanism as a multifunctional separator for lithium-sulfur batteries contributes to ultra-high initial discharge specific capacity

The critical factors that limit the electrochemical performance of lithium-sulfur (Li-S) batteries are mainly the “shuttle effect” of polysulfides and the slow redox reaction between lithium polysulfides (LiPSs). Herein, a nano-sphere-type material self-assembled from tin disulfide nanosheets is designed and applied to the Li-S cell separator in this work. The SnS2@PP modified separator not only acts as a dual restriction for LiPSs by chemisorption and physical barrier. At the same time, it improves the catalytic activity of the redox reaction between LiPSs. The SnS2 has extremely high electrochemical activity. There, a portion of the lithium ions can be inserted into SnS2 to form LixSnS2 and contribute to the capacity during the first discharge of the battery. In addition, LixSnS2 possesses a high degree of stability, and it does not undergo further de-alloying reactions even at the high potential of the Li-S cell. The benefit is that the steady-state LixSnS2 acts as a lithium-containing substance. It can form special Li+ channels on the surface of the separator, thus greatly improving the efficiency of Li+ transport. The results showed that the SnS2@PP-based cell exhibited extremely high initial discharge specific capacity (1477 mAh g−1 at 0.1 C) and excellent rate performance (631 mAh g−1 at 5 C). Even after 1000 cycles at 2 C, the cell exhibited a low decay rate of 0.06% per cycle on average. In addition, the superior electrochemical performance was obtained even with a high sulfur loading of 5.1 mg cm−2 and low electrolyte of E/S = 8 µL mg−1.