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

Abstract

Lithium-sulfur (Li-S) batteries with high theoretical energy densities of ∼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.