Porphyrin-based covalent organic framework/graphene composite separator synergistically enhances the adsorption and catalysis of lithium polysulfides

Abstract

Lithium–sulfur batteries are considered a prime candidate for next-generation energy storage owing to their ultrahigh theoretical energy density of 2600 Wh kg⁻¹. However, the shuttle effect of soluble lithium polysulfides (LiPSs) leads to rapid loss of active materials and severe capacity decay. Herein, we synthesized a porphyrin-based covalent organic framework/graphene composite separator (H₂Por-TPE-COF@GO) via a Schiff base condensation reaction on amine-functionalized graphene, achieving covalent bonding between the covalent organic framework and graphene. Benefiting from the ordered microporosity of the COF and the high conductivity and mechanical flexibility of graphene, the composite separator synergistically enhances physical blocking of LiPSs. At a current density of 1C, the cell delivers an initial capacity of 763 mAh g⁻¹ and retains 604 mAh g⁻¹ after 500 cycles (70% retention), significantly outperforming pure COF and physical mixture controls. This work provides a new strategy for in situ coupling of crystalline porous polymers with two-dimensional conductive substrates, offering important insights for the commercialization of high-energy, and long-life lithium–sulfur batteries.