A novel sulfonated polyimide membranes inserting flexible decane chain and rigid triptycene-based crosslinked network for vanadium redox flow batteries

To address the trade-off between proton conductivity and vanadium ion permeability in sulfonated polyimide (SPI) membranes, we introduce a novel flexible decane chain and rigid triptycene-based crosslinked SPI (SPI-DH) with rigid twisted groups and amine-functionalized networks. Incorporating flexible decane chains not only enhances the membrane-forming ability but also remarkably reduces the likelihood of nucleophilic attacks by water on the imide bonds, thereby strengthening the membrane's hydrolytic stability. The rigid structure increases chain spacing and hydrophilic-hydrophobic phase separation, while amine groups conduct protons by forming hydrogen bonds with sulfonate groups and construct crosslinked networks to suppress vanadium ion permeation. SPI-DH-60 exhibits a high proton conductivity of 0.101 S cm −1 and an ion selectivity of 7.32 × 10 4 S min cm −3 , achieving a high energy efficiency of 80.39 % at 160 mA cm −2 and over 400 cycles. These results demonstrate its potential for vanadium redox flow batteries (VRFBs). The study employs a flexible decane chain and a rigid triptycene-based crosslinked network to optimize the membrane's microstructure and chemical composition. It reveals the remarkable effectiveness of the SPI-DH membrane in enhancing proton conductivity and reducing vanadium ion permeability, thereby improving the overall performance of all-vanadium redox flow batteries and providing strong support for new energy storage applications. • High-performance membrane for vanadium redox flow batteries. • Designed novel sulfonated PI (SPI-DH) with flexible decane and rigid triptycene. • Low area resistance, excellent ion selectivity. • High efficiencies, ultralow self-discharge rate and superior cycling stability.