Tuning the structure and composition of graphite-phase polymeric carbon nitride/reduced graphene oxide composites towards enhanced lithium-sulfur batteries performance

Graphical abstract: C₃N₄/rGO aerogels were synthesized through hydrothermal reaction, which exhibit strong absorbtion to lithium polysulfides and enhance the longevity of sulfur electrode. Display Omitted -- Highlights: •C₃N₄/rGO aerogels with unique nanostructure were synthesized by simple solvothermal methods. •The interconnected aerogel provides both physical barrier and chemical absorption to deter the dissolution of polysulfides into the electrolyte. •It has been identified that the C₃N₄/rGO-sulfur cathode with 1:2 mass ratio of C₃N₄ and rGO (CG12) exhibited the optimized performance. -- Abstract: Lithium-sulfur (Li-S) batteries have been attractive alternatives to lithium-ion (Li-ion) batteries due to the high theoretical capacity of sulfur cathode. However, the polysulfide shuttling effect is detrimental to the long-term cycling stability. Chemically absorptive host materials provide an effective way to mitigate the dissolution of lithium polysulfide. Carbon nitride (C₃N₄) is one of the effective host materials with strong interaction with polysulfide species. The low electronic conductivity, however, is unfavorable for high sulfur utilization. In this work, we report the controlled synthesis of porous, well-interconnected C₃N₄/reduced graphene oxide (rGO) aerogels as hybrid sulfur host using a simple hydrothermal reaction followed by freeze-drying, which combines the structural merits of both highly conductive rGO networks and chemically active C₃N₄. By further tuning the structure/morphology and the ratio between C₃N₄ and rGO, we have demonstrated the C₃N₄/rGO composites with optimized 1:2 ratio of C₃N₄:rGO (termed as CG12) exhibits not only very high sulfur utilization but also excellent rate capability compared to other C₃N₄/rGO composites, pure rGO, and C₃N₄. The compositionally and structurally tailored CG12 also shows stable cycling performance over 400 cycles with a low decay rate of 0.09% per cycle.