Nitrogen doped yolk-shell carbon spheres as cathode host for lithium-sulfur battery

Abstract

Suppressing the shuttle effect while maintaining high sulfur content is the primary challenge for the development of lithium-sulfur (Li-S) batteries. An effective encapsulator for Li-S battery is supposed to have enough void space for sulfur accommodation and alleviation of volume expansion. Moreover, an excellent electronic conductivity is also crucial for high sulfur utilization. Thus, we designed mesoporous nitrogen doped yolk-shell carbon (NYSC) spheres as novel sulfur encapsulators. This unique structure design greatly fulfills the synergistic effect of chemisorption and physisorption for polysulfides, specially at high sulfur loading. The inner mesoporous “yolk” acts as a sulfur reservoir to entrap polysulfide species. Meanwhile, the outer “shell” serves as a physical barrier to alleviate the dissolution of polysulfides. Additionally, the doped nitrogen atom in carbon lattice can modify the electron distribution, introduce more defects and active sites for the chemisorption of polysulfides, improve the reversibility of Li2S/polysulfide/S conversion and the electronic conductivity, contributing to the enhanced electrochemical performance for Li-S batteries (a high specific capacity of 1329 mA h g−1 at 0.2 C and an extended cycle life).