Cross-Linked Quinuclidinium-Based Membranes Achieving Exceptional Alkaline Durability in Alkaline Zinc–Iron Flow Batteries

Alkaline zinc–iron flow batteries (AZIFBs) are considered promising candidates for grid-scale energy storage due to their inherent safety, cost-effectiveness, and high energy density. However, their long-term cycling stability is largely limited by chemical and mechanical membrane degradation in strongly alkaline environments, as well as the consequent damage caused by zinc dendrites. In this study, we develop a robust alkaline membrane by the configurational design of an all-carbon phenyl backbone and N -methylquinuclidinium groups, in which the alkaline-stable cross-linking polyphenylene oxide (PPO) enhances interchain cohesion. As a result, the membrane retained both chemical and mechanical stability without structural decomposition after immersion in 4 M NaOH for 1500 h at 80 °C. Moreover, it delivers exceptional mechanical resilience to avoid zinc dendrite piercing, even working in high alkaline electrolytes under high areal capacities. The AZIFB operates stably for over 1000 h at an ultrahigh areal capacity of 200 mAh cm –2, with an average Coulombic efficiency of 96.66% and an energy efficiency of 84.86%. This work guides the design of chemically robust membranes in alkaline zinc-based flow battery systems.