An ion sieving conjugated microporous thermoset ultrathin membrane for high-performance Li-S battery

Lithium-sulfur (Li-S) battery is an attractive candidate for next-generation energy storage devices due to its high theoretical energy density, but its practical applications are hindered by polysulfides shuttling and lithium dendrite growth. In this study, a solution-processable conjugated microporous thermoset (CMT) was used as an ultrathin ion sieving layer on a commercial PP separator. The CMT layer is as thin as ∼200 nm and possesses continuous sub-nanochannels. Molecular dynamic simulations show that the nanoporous polymeric network allows Li-ion passage while blocking polysulfides shuttling between the electrodes based on size-exclusive effects. In addition, the CMT layer acts as a buffer zone for the uniform distribution of Li ions on the surface of the Li anode to suppress the growth of lithium dendrites. As a result, Li-S battery employing the CMT-modified polypropylene separator achieves a high initial capacity of 849.6 mAh g⁻¹ with an ultralow attenuation rate of 0.037% per cycle over 1000 cycles at 1 C, as well as a capacity of 619.0 mAh g⁻¹ at an ultrahigh current density of 10 C. Remarkably, it exhibits a capacity of 727.8 mAh g⁻¹ with ∼ 77% capacity retention over 500 cycles lifespan at a high current density of 5C, showing great potential for practical high-performance Li-S batteries.