Regulating Anionic Environment of COF@CNT Composite for Kinetics-boosted and Wide-temperature Lithium-Sulfur Batteries

Abstract

Lithium–sulfur (Li–S) batteries offer high theoretical energy density but are limited by issues such as polysulfide shuttling and poor performance across a wide temperature range. To overcome these challenges, we developed ionized COF@CNT composites and studied how their anionic centers influence polysulfide adsorption and conversion. By replacing Br⁻ in EB-COF-Br with LiTFSI and LiOTF, we tailored the COF interface to improve ion conductivity and the Li+ transference number. It demonstrated that the OTF anion was more effective in reducing charge transfer resistance and promoting lithium sulfide formation. In situ Raman spectroscopy confirmed that the COF-OTF@CNT-modified separator effectively suppressed polysulfide shuttling. Electrochemical tests showed excellent cycling stability and rate performance, with the modified cell achieving 800 cycles at 1 C with only 0.058% capacity loss per cycle, and 89.3% capacity retention after 200 cycles at 0 °C. These findings highlight chemical tuning of the COF@CNT anionic centers as a promising strategy to enhance Li–S battery performance, particularly in extreme temperature environments.