Enhancing the catalytic conversion of polysulfides utilizing a covalent organic framework–carbon nanotube interlayer

Abstract

Lithium–sulfur (Li–S) batteries, characterized by their exceptionally high theoretical energy density of 2600 Wh kg⁻¹, encounter significant challenges related to polysulfide shuttling and slow redox kinetics. Covalent organic frameworks (COFs) have demonstrated potential in addressing these challenges; however, traditional synthesis methods are often hindered by inefficiencies and limitations in scalability. In this study, we introduce a triazine-based COF–carbon nanotube (CTF–CNT) composite separator, synthesized via a scalable vacuum-assisted strong-acid polymerization technique. The AA-stacked CTF structure, enriched with nitrogen-active sites, establishes an electrostatic catalytic field that effectively confines polysulfides and enhances their conversion kinetics. Coupled with the improved conductivity provided by CNTs, the composite separator exhibits dual functionality: (1) superior lithium-ion transport (t_Li⁺ = 0.60, σ_Li⁺ = 5.16 × 10⁻⁴ S cm⁻¹) and (2) efficient polysulfide adsorption through chemical-electrocatalytic coupling. Under practical conditions, with a sulfur loading of 5 mg cm⁻² and an electrolyte volume of 10 μL mg⁻¹, CTF–CNT cells achieve a capacity of 599 mA h g⁻¹ after 100 cycles at 0.5C, with minimal polarization (ΔE = 281 mV). In situ Raman spectroscopy indicates full reversibility of sulfur redox reactions, whereas symmetric cell experiments exhibit stable lithium plating and stripping over a duration of 1400 hours. This study introduces a scalable materials design framework for high-energy batteries, effectively addressing shuttle suppression, kinetic enhancement, and the inhibition of lithium dendrite formation.