Ion-Regulating Membranes with Surface-Enriched Charge Networks Enabling Stable Zinc-Manganese Flow Batteries

Zinc-based flow batteries are promising for sustainable energy storage owing to their high energy density and eco-friendliness. When coupling with Mn²⁺/MnO₂ posolyte, the zinc-manganese flow batteries promise an ultra-low electrolyte cost (0.0039 $ Ah^-1). However, their practical application is limited by low areal capacity (<20 mAh cm^-2) and poor lifespan (<100 cycles with accumulated capacity < 2000 mAh cm^-2), associated with proton crossover and zinc dendrite formation. To address the two bottlenecks, an ion-regulating membrane with surface-enriched positive charges of Zn²⁺ crosslinked networks is proposed. The enriched-charged networks amplify H⁺ retention (60% elevated proton transport barrier to 0.104 eV) via imposing charge-enhanced dehydration barriers and nitrogen-groups synergism, leveraging the higher ionic potential of protons to discriminate the conduction ions (K⁺). Simultaneously, the surface charges electrostatically guide the uniform distribution of near-electrode zinc ions for zinc-oriented growth without dendrites. The synergistic strategy achieves a near-neutral zinc-manganese flow system with a record accumulated capacity of 6510 mAh cm^-2 (>200 cycles) at 30 mA cm^-2, high areal capacity of 100 mAh cm^-2 (130.1 mWh cm^-2) at 20 mA cm^-2, representing one of the most stable zinc-manganese flow batteries reported. This study provides an effective membrane design strategy for low-cost and high-energy-density zinc-based flow batteries.