Enabling a Robust Long-Life Zinc-Iodine Flow Battery by Stabilizing the Zinc Anode in a Halide-Rich Electrolyte.

The growing demand for grid-scale energy storage calls for safe and low-cost solutions, for which zinc-iodine flow batteries (ZIFBs) are highly promising. However, their practical application is critically hindered by two issues: accumulation of insoluble solid iodine at the cathode and zinc dendrite growth at the anode. While halide-rich electrolyte can address the former, the anode instabilities remain a major obstacle. Here, a holistic solution is presented by introducing a dual-function additive, glucosamine sulfate (GS), into a halide-rich electrolyte. GS reconfigures the Zn solvation structure by displacing coordinated water to accelerate Zn deposition kinetics, while preferentially adsorbing on the anode surface to form a water-poor layer that inhibits parasitic side reactions and guides uniform, crystallographically-oriented deposition along the Zn (002) crystal plane. As a result, a ZIFB with a zero-excess zinc anode and anolyte demonstrates robust durability, surpassing 500 cycles at 40 mA cm and 30 mAh cm. This delivers an attractive cumulative plating capacity of 15 Ah cm with a near-theoretical Coulombic efficiency of 99.6% and a high energy efficiency of 81.9%. This electrolyte engineering strategy, which stabilizes the anode within an advanced cathode chemistry, paves the way for highly durable and practical high-energy flow batteries.