Ion Selective Covalent Organic Framework Enabling Enhanced Electrochemical Performance of Lithium–Sulfur Batteries

Ion selective separators with the capability of conducting lithium ion and blocking polysulfides are critical and highly desired for high-performance lithium–sulfur (Li–S) batteries. Herein, we fabricate an ion selective film of covalent organic framework (denoted as TpPa-SO₃Li) onto the commercial Celgard separator. The aligned nanochannels and continuous negatively charged sites in the TpPa-SO₃Li layer can effectively facilitate the lithium ion conduction and meanwhile significantly suppress the diffusion of polysulfides via the electrostatic interaction. Consequently, the TpPa-SO₃Li layer exhibits excellent ion selectivity with an extremely high lithium ion transference number of 0.88. When using this novel functional layer, the Li–S batteries with a high sulfur loading of 5.4 mg cm^–2 can acquire a high initial capacity of 822.9 mA h g^–1 and high retention rate of 78% after 100 cycles at 0.2 C. This work provides new insights into developing high-performance Li–S batteries via ion selective separator strategy.