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 Zn²⁺ solvation structure by displacing coordinated water to accelerate Zn²⁺ 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^-2 and 30 mAh cm^-2. This delivers an attractive cumulative plating capacity of 15 Ah cm^-2 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.