Architecting Redox-Active Framework Interfaces for Synergistic Sulfur Adsorption and Catalysis in Lithium–Sulfur Batteries

The rational design of redox-mediating framework architectures offers a powerful strategy to overcome the polysulfide shuttling and sluggish conversion kinetics that limit lithium–sulfur (Li–S) batteries. Here, we report a new covalent organic framework, TUS-44, constructed from tetrathiafulvalene (TTF)-based 4,4',4'',4'''-([2,2'-bi(1,3-dithiolylidene)]-4,4',5,5'-tetrayl)tetraaniline and benzo[18]crown-6-derived 4,4′,4′′,4′′′-(6,7,9,10,17,18,20,21-octahydrodibenzo[b,k][1,4,7,10,13,16]hexaoxacyclooctadecine-2,3,13,14-tetrayl) tetrabenzaldehyde linkers. The resulting imine-linked, π-conjugated framework integrates sulfur-rich redox centers and electron-delocalized backbones, establishing site-specific Li–S coordination and dynamic charge mediation. When coupled with conductive graphene to form an interfacial TUS-44@G architecture, the hybrid layer functions as a redox-active chemisorptive interface that governs the equilibrium of soluble polysulfides, promotes bidirectional electron transfer, and stabilizes intermediate species throughout cycling. This synergistic chemical–electronic coupling yields remarkable electrochemical performance: a high reversible capacity of 1455.7 mA h g⁻1 at 0.2 A g⁻1, excellent rate capability of 773 mA h g⁻1 at 10 A g⁻1, and outstanding durability with 0.034% capacity fading per cycle over 1000 cycles at 5 A g⁻1. A Li–S pouch cell incorporating TUS-44@G further delivers an outstanding initial energy density of ~674 Wh kg⁻1 at 0.05 A g⁻1 (sulfur loading 44.558 mg), underscoring the practical potential of architecting redox-catalytic framework interfaces for high-energy, durable Li–S batteries.