Ion channel-gated covalent organic framework membrane for sustainable lithium–sulfur batteries

Lithium-sulfur (Li-S) batteries hold promise as a compelling alternative to current state-of-the-art Li-ion batteries due to their high theoretical capacity, low cost and the natural abundance of sulfur. However, the practical realization of Li-S batteries has been plagued by the longstanding trade-off issue between polysulfide shuttle suppression and Li⁺ transport. Here, we report an ion channel-gated covalent organic framework (COF) as an ionic diode membrane strategy to address this conflicting requirement. By tuning the chemical structure of tethered anions, the resulting COF features 1D anionic channels with optimized charge delocalization and pore size. The bulky anions enhance Li⁺ dissociation and conduction while effectively repelling polysulfides dissolved from S cathodes. Additionally, the COF ionic diode mitigates self-discharge and inhibits parasitic reactions. Consequently, Li-S cells assembled with the COF ionic diode improve charge/discharge capacities and cycle life under constrained operating conditions.