Synergetic Covalent and Spatial Confinement of Sulfur Species by Phthalazinone-Containing Covalent Triazine Frameworks for Ultrahigh Performance of Li-S Batteries.

Lithium-sulfur (Li-S) batteries severely suffer from the shuttling of soluble polysulfides intermediates, insulation of sulfur and lithium sulfides, and volumetric expansion of sulfur electrodes, which result in the fast capacity decay and low utilization of active materials. To overcome these issues, a new type of porous phthalazinone-based covalent triazine frameworks (P-CTFs) with inherent N and O atoms has been in situ grown onto conductive reduced graphene oxide (rGO) by the sulfur-mediated cyclization of dinitrile monomers to afford the S/P-CTF@rGO hybrids. The well-designed structure endows the S/P-CTF@rGO composites with several features for enhanced Li-S batteries: (i) the nanoporous structure can spatially trap the sulfur species within the P-CTFs; (ii) the covalent binding of sulfur and polar groups of phthalazinone and triazine in P-CTFs exhibits strong chemical attachment and adsorption with polysulfides and further limits the diffusion of polysulfides; (iii) the conductive rGO and semiconductive P-CTFs help faster electronic transportation and accelerate the electrochemical process. Therefore, the S/P-CTF@rGO cathodes show greatly enhanced electrochemical performances with a high initial specific capacity of 1130 mAh g-1 at 0.5C and a good capacity retention of 81.4% after 500 cycles, indicating only 0.04% degradation per cycle.