Frogspawn inspired hollow Fe3C@N-C as an efficient sulfur host for high-rate lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries with high theoretical energy densities of similar to 2600 W h kg(-1) have been recognized as a promising energy storage device. However, the practical application of Li-S batteries is still limited by the cycle stability and rate capability, which is highly relied on the well-designed cathode material. Inspired by the unique structure of frogspawn in Nature, a hollow Fe3C@N-C with frogspawn-like architecture was successfully constructed as a highly efficient sulfur host in this paper. Derived from a Prussian blue self-template, Fe3C@N-C possesses a metal-like Fe3C spawn core and the high conductivity of an N-doped carbon shell. This unique structure enables a large surface area, fast e(-)/Li+ transport, as well as a large hollow space for the volumetric expansion of the sulfur cathode. Moreover, with the N-doped carbon shell and the polar Fe3C core, the trapping and catalytic conversion of intermediate polysulfides are also facilitated. The strongly coupled interaction of polar Fe3C and polysulfides is confirmed by both theoretical calculations and electrochemical performance. Specifically, the Fe3C@N-C/S electrode presents a high capacity of 1351 mA h g(-1) at 0.1C with the Fe3C@N-C as an integrated sulfur host. In particular, the rate capability and cycling stability of the Fe3C@N-C/S electrode is outstanding. It displays a high capacity of 792 mA h g(-1) at 5C and a low capacity decay rate of 0.08% per cycle at 0.5C after 400 cycles. This work opens a convenient and economical avenue to design a frogspawn-like hollow metal carbide/carbon as an efficient sulfur host for advanced Li-S batteries.