Hierarchical, nitrogenous hollow carbon spheres filled with porous carbon nanosheets for use as efficient sulfur hosts for lithium-sulfur batteries

Hollow carbon materials modified by nitrogen are ideal sulfur hosts owing to their high conductivity, large specific surface area, physical confinement and nitrogen polar sites and have been adopted in sulfur cathodes to design high performance lithium-sulfur batteries (LSBs). However, non-hierarchical nitrogenous hollow carbon cannot guarantee sufficient contact between sulfur and carbon materials, leading to the slow reaction rate of sulfur and inadequate adsorption of LPS, both of which should occur on the surfaces of the carbon material only. Therefore, it ishighly necessary to synthesize hierarchical hollow nitrogenous carbon via a facile method that is neither difficult nor complex. Herein, we propose a novel method to fabricate nitrogenous hollow carbon spheres filled with porous carbon nanosheets (NHCS-PCS) and prove that using these hierarchical NHCS-PCS as a sulfur host for LSBs is more efficient than using traditional nitrogenous hollow carbon spheres (NHCS). NHCS-PCS with a hierarchical structure can 1) ensure sufficient contact between sulfur and carbon, which occurs as a result of the dispersed distribution of sulfur in the filled porous carbon nanosheets, thus promoting the reaction of sulfur and adequate adsorption of LPS, simultaneously; 2) provide a sufficient number of adsorption sites and enhance the physical entrapment for LPS, because the NHCS-PCS have a higher content of nitrogen and larger specific surface area than the NHCS. Because of these benefits, the NHCS-PCS/sulfur composite cathode exhibits a high sulfur utilization, resulting in a high discharge capacity of 1516 mAh/g at 0.1 C, fast reaction kinetics (1169, 960 and 626 mAh/g at 0.2, 0.5 and 1 C, respectively) and a stable long-term cycling performance (86.5% capacity retention after 250 cycles at 0.5 C, which is equivalent to a decay of 0.054% per cycle). Our work provides a facile method of preparing hollow and hierarchical carbon, which is a promising sulfur host for LSBs.