Fe3C-Decorated Folic Acid-Derived Graphene-like Carbon-Modified Separator as a Polysulfide Barrier for High-Performance Lithium-Sulfur Batteries

The lithium-sulfur (Li-S) battery has been regarded as an important candidate for the next-generation energy storage system due to its high theoretical capacity (1675 mAh g−1) and high energy density (2600 Wh kg−1). However, the shuttle effect of polysulfide seriously affects the cycling stability of the Li-S battery. Here, a novel Fe3C-decorated folic acid-derived graphene-like N-doped carbon sheet (Fe3C@N-CS) was successfully prepared as the polysulfide catalyst to modify the separator of Li-S batteries. The porous layered structures can successfully capture polysulfide as a physical barrier and the encapsulated Fe3C catalyst can effectively trap and catalyze the conversion of polysulfide, thus accelerating the redox reaction kinetics. Together with the highly conductive networks, a cell with the Fe3C@N-CS-modified separator evinces superior cycling stability with 0.06% capacity decay per cycle at 1 C rate over 500 cycles and excellent specific capacity with an initial capacity of 1260 mAh g−1 at 0.2 C. Furthermore, at a high sulfur loading of 4.0 mg cm−2, the batteries also express superb cycle stability and rate performance.