Functional fluorinated COF layers for enhanced Li+ transport and suppressed polysulfide shuttle in Li–S batteries

To achieve the practical application of high energy density lithium–sulfur (Li–S) batteries, it is essential not only to enhance lithium-ion (Li + ) transport but also to effectively suppress the lithium polysulfides (LiPSs) shuttle effect, which remains challenge for the conventional commercial separators. In this study, a fluorinated covalent organic framework (Tp-TFAB COF) material with high selective permeability was employed to modify separators for Li–S batteries. The fluorinated Tp-TFAB COF layer can effectively enhance Li + conduction while providing electrostatic shielding against LiPSs, which were also confirmed by density functional theory calculations. As a result, Li–S batteries with Tp-TFAB/PP-modified separators retained 79.4 % of their initial capacity after 800 cycles at a 0.5C rate, with a low capacity decay of 0.026 % per cycle. Even at a high sulfur loading (7.3 mg cm −2 ), the batteries exhibited an impressive areal capacity of 5.83 mAh cm −2 . This work highlights the selective functionality of the fluorinated COFs nanoscopic channels, demonstrating its potential for applications in energy storage and beyond.