Electrostatic polarity-regulated, vinylene-linked cationic covalent organic frameworks as an ionic sieve membrane for long-cyclable lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have garnered attention as a promising alternative to commercial Li-ion batteries owing to their high theoretical energy density and the natural abundance of sulfur. However, the uncontrolled dendrite growth of Li metal anodes and shuttle effect of polysulfides have plagued their practical application. To address these issues, here, we present electrostatic polarity-regulated, vinylene-linked cationic covalent organic frameworks (COFs) as a class of ionic sieve membranes. The electrostatic polarity of the COFs was controlled by varying the counter anions adjacent to the cationic framework. The higher electrostatic polarity achieved with a bulkier anion, combined with the one-dimensional nanochannels of the COFs, suppressed polysulfide crossover, while facilitating Li+ conduction, demonstrating the viability of the ionic sieving effect of the membrane. Consequently, the Li-S cell fabricated with the COF-based ionic sieve membrane exhibited a low capacity degradation of 0.041 % per cycle over 1000 cycles at a fast current rate of 1 C.