Covalent Organic Frameworks for Lithium-Sulfur Batteries: Multifunctionality, Catalytic Mechanisms, and In Situ Characterization.

Lithium-sulfur batteries (LSBs) are promising next-generation energy storage systems due to their high theoretical energy density and cost-effectiveness. However, challenges such as polysulfide shuttle, sluggish redox kinetics, and electrode instability hinder their practical applications. Covalent organic frameworks (COFs), featuring high porosity, tunable functionality, and structural regularity, have emerged as versatile materials to address these issues. This review systematically summarizes recent advances in COF-based strategies for LSBs, including their multifunctional roles as sulfur hosts, separators/interlayers, and catalytic additives. The predominant catalytic mechanisms associated with COFs are further elucidated, with specific focus being placed on electrostatic field catalysis, supramolecular channel catalysis, redox-mediated catalysis, and metal-coordination catalysis. While conventional characterization techniques have been extensively described in previous reviews, particular emphasis is placed on the application of in situ characterization techniques, such as Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction (XRD), which offer mechanistic insights into COF-catalyzed polysulfide conversion. This review aims to provide a comprehensive understanding of the structure-function-performance relationship of COFs and guide the rational design of next-generation COF-based materials for high-performance LSBs.