Fluorinated,\nSulfur-Rich, Covalent Triazine Frameworks for Enhanced Confinement\nof Polysulfides in Lithium–Sulfur Batteries

Abstract

Lithium–sulfur\nbattery represents a promising class of energy storage technology\nowing to its high theoretical energy density and low cost. However,\nthe insulating nature, shuttling of soluble polysulfides and volumetric\nexpansion of sulfur electrodes seriously give rise to the rapid capacity\nfading and low utilization. In this work, these issues are significantly\nalleviated by both physically and chemically restricting sulfur species\nin fluorinated porous triazine-based frameworks (FCTF-S). One-step\ntrimerization of perfluorinated aromatic nitrile monomers with elemental\nsulfur allows the simultaneous formation of fluorinated triazine-based\nframeworks, covalent attachment of sulfur and its homogeneous distribution\nwithin the pores. The incorporation of electronegative fluorine in\nframeworks provides a strong anchoring effect to suppress the dissolution\nand accelerate the conversion of polysulfides. Together with covalent\nchemical binding and physical nanopore-confinement effects, the FCTF-S\ndemonstrates superior electrochemical performances, as compared to\nthose of the sulfur-rich covalent triazine-based framework without\nfluorine (CTF-S) and porous carbon delivering only physical confinement.\nOur approach demonstrates the potential of regulating lithium–sulfur\nbattery performances at a molecular scale promoted by the porous organic\npolymers with a flexible design.