Ultralong-Life Zinc-Bromine Flow Battery with Low Polybromide Shuttle and Stable Zinc Interface

Zinc-bromine (Zn-Br) flow batteries are promising for grid-scale energy storage due to their high safety, low cost, and scalable architecture. However, their application remains constrained by cathode-side polybromide shuttle and anode-side Zn dendrite formation and hydrogen evolution reactions (HER). Here, we propose a bidomain engineering strategy that employs acetylcholine (ACh⁺) as a dual-functional electrolyte additive to simultaneously address the challenges of both sides. On the cathode side, the quaternary ammonium group of ACh⁺ complexes with polybromides upon charging to increase their molecular size, thereby effectively inhibiting the polybromide shuttle. On the anode side, the acetyl group of ACh⁺ rapidly absorbs onto the Zn surface to form a water-depleted interface, inducing uniform Zn plating/stripping with suppressed HER. Consequently, the cycling life of Zn-Br flow batteries with a single ACh⁺ additive is extended by nearly 80-fold, from 80 cycles to over 6400 cycles, demonstrating highly durable cycling stability, together with an outstanding cumulative plating capacity of 128 Ah cm^-2. This finding demonstrates that dual-function electrolyte design provides a viable pathway for grid-scale application of high-rate and long-life Zn-Br flow batteries.