A High-Voltage Alkaline Zinc-Iodine Flow Battery Enabled by a Dual-Functional Electrolyte Additive Strategy

Zinc-iodine flow batteries have attracted huge attention for distributed energy storage devices owing to high inherent safety, suitable redox potential, and superior solubility. However, the zinc dendrite growth and the limited open circuit voltage significantly deteriorate zinc anode reversibility and hinder further technological advances for high-energy density zinc-iodine flow batteries. Herein, an alkaline zinc-iodine flow battery is designed with potassium sodium tartrate (PST) as an effective additive for Zn(OH)₄²⁻ anolyte, which enables a high open circuit voltage of 2.385 V and meanwhile realizes a reversible zinc plating/striping reaction. Both experimental investigation and theoretical calculation confirm that the PST interacts strongly with Zn²⁺ by replacing the OH⁻ from the Zn(OH)₄²⁻ solvation shell and thus ameliorates the kinetics of the zinc deposition reaction. Besides, PST adsorbs preferentially on the electrode surface and effectively regulates the Zn²⁺ diffusion flux, thereby minimizing the formation of zinc dendrites and avoiding the formation of dead zinc. Benefitting from PST additives, the zinc-iodine flow battery demonstrates a remarkable combination of improved power density (616 mW cm⁻²), enhanced energy density (185.18 Wh L⁻¹) as well as prolonged cycling performance at 120 mA cm⁻², which presents a new pathway to develop reliable zinc anode for high-voltage flow batteries.