Isothermal sulfur condensation into carbon nanotube/nitrogen-doped graphene composite for high performance lithium-sulfur batteries

Nitrogen-doped graphene (NG) is a promising material for fabricating high-performance lithium-sulfur batteries. Here a facile hydrothermal method was used to synthesize the NG and then the composite of NG and SWCNT (NG/SWCNT) was obtained by mixing with single-walled carbon nanotubes (SWCNT) via a simple ultrasonic method. Finally, the NG/SWCNT-sulfur composite (NG/SWCNT-S) is synthesized via an isothermal method that enables rapid vapor infiltration of sulfur into carbon nanotubes. The resulting sulfur-containing cathode shows a good capacity performance, reaching high initial capacities of 1199.6 mAh g(-1) at 0.1 C and 725.2 mAh g(-1) at 1 C. The optimized electrochemical performance can be attributed to the NG addition which leads to an effective improvement of sulfur utilization and seizing polysulfides during cycling. Moreover, we show that the vapor infiltration method based on the thermodynamics of capillary condensation on nanoscale surfaces offers a new idea for assembling cathode, compared to the traditional melt infiltration method.