Tailoring poly(m-phenylene isophthalamide) separator via isopropanol-induced phase separation for high-performance lithium‑sulfur batteries

Lithium‑sulfur batteries are promising energy storage systems but remain limited by the poor thermal stability and severe polysulfide shuttle effect associated with conventional polyolefin separators. Herein, a porous poly(m-phenylene isophthalamide) (PMIA) separator was fabricated via an isopropanol (IPA)-induced phase separation strategy to regulate pore structure and ion transport behavior, in which polyvinylpyrrolidone (PVP) served as a bifunctional additive for pore formation and physical crosslinking regulation. Compared with rapid water-induced phase separation, the delayed demixing process induced by IPA promoted the formation of a uniform sponge-like porous architecture with improved pore connectivity and electrolyte affinity. Benefiting from the interconnected nanoporous framework, polar amide groups, and the synergistic effect of PVP-regulated pore structure, the optimized PMIA separator exhibited enhanced ionic conductivity, increased Li + transference number, strong polysulfide adsorption capability, and excellent thermal dimensional stability. Consequently, the assembled lithium‑sulfur batteries delivered improved rate capability and stable long-term cycling performance, maintaining a reversible capacity of 540 mAh g −1 after 200 cycles at 0.2C and 420 mAh g −1 after 300 cycles at 1C. This work provides an effective strategy for constructing thermally stable aramid separators for safe and high-performance lithium‑sulfur batteries.