Synergy of O2 Permeance and H2O Resistance by PIM‐Enhanced PDMS Composite Membranes for “Closed‐Type” Aprotic Li‐Air Batteries

Abstract Aprotic Li‐O₂ batteries exhibit ultra‐high energy density through the redox reaction of O₂. However, their open‐structure design makes them prone to water infiltration and electrolyte leakage. Traditionally, dense and thick oxygen‐permeable membranes (OPMs) are employed to prevent H₂O intrusion, but this approach limits O₂ permeance and constrains charge current densities. To address the trade‐off between O₂ permeance and H₂O resistance, a novel double‐laminated film (DLF) is proposed as an OPM. This innovative design integrates a thin polydimethylsiloxane (PDMS) layer, known for its excellent H₂O resistance, onto a polymer of intrinsic microporosity (PIM‐1) substrate, which offers high O₂ permeability. The resulting thin composite OPM (<40 µm) enables Li‐air batteries to operate continuously for 90 cycles (180 h) in ambient air with a relative humidity of 50 ± 5% at 1000 mA g⁻¹, owing to the synergistic effects of the OPM's exceptional O₂ permeance (6881 Barrer, 215 GPU) and its effective mitigation of H₂O intrusion. The selective transport of O₂ and H₂O is facilitated by the hydrophobic apertures of the PDMS and PIM‐1 layers, which exploit their kinetic differences. This work highlights the potential of high‐free‐volume, microporous polymers, and DLF architectures for advancing OPMs in aprotic Li‐air battery applications.