Ultra-thin Fe3C nanosheets promote the adsorption and conversion of polysulfides in lithium-sulfur batteries

Rational design of hierarchical porous materials with comprehensive properties, e.g. good conductivity, fine dispersibility for sulfur, strong adsorption and catalytic abilities to polysulfides (LiPSs), is urgently needed for the practical application of lithium-sulfur batteries (Li-S batteries). Here, based on density functional theory (DFT) computational results and the design concept of efficient, low-cost and environmental friendliness, we report an ultra-thin (~ 1 nm) Fe3C nanosheets growing on mesoporous carbon (Fe3C-MC) with large specific surface area of 686.9 m2 g-1 and pore volume of 6.52 cm3 g-1. Meanwhile, the formation mechanism of two-dimensional Fe3C is revealed according to DFT results. In the Fe3C-MC composite, the mesoporous carbon constructs a conductive network for dispersion of sulfur species, while Fe3C nanosheets play a key role in electronic transmission, LiPSs adsorption and conversion in Li-S batteries. As a result, the Fe3C-MC composite delivers a high initial capacity of 1530 mA h g-1 at 0.1 C, and a capacity of 699 mA h g-1 after 100 cycles at 0.5 C at a super-high sulfur loading of 9.0 mg cm-2, meaning a specific area capacity of 6.291 mA h cm-2. Such sulfur host is expected to accelerate the practical applications of Li-S batteries benefiting from the low-cost and large-scale process.