Ambipolar zinc-polyiodide electrolyte for a high-energy density aqueous redox flow battery

TLDR

Redox flow batteries are attractive for energy storage but are limited by low energy density (~25 Wh l⁻¹). We report a high‑energy‑density aqueous zinc‑polyiodide flow battery. Adding ethanol forms a ligand between hydroxyl oxygen and zinc, widening the stable temperature window from –20 °C to 50 °C and reducing zinc dendrite growth, as shown by NMR, DFT, and flow tests. The battery achieves 167 Wh l⁻¹ discharge energy density with a near‑neutral 5.0 M ZnI₂ electrolyte and, due to its benign, acid‑free composition, is a promising candidate for diverse energy‑storage applications.

Abstract

Abstract Redox flow batteries are receiving wide attention for electrochemical energy storage due to their unique architecture and advantages, but progress has so far been limited by their low energy density (~25 Wh l −1 ). Here we report a high-energy density aqueous zinc-polyiodide flow battery. Using the highly soluble iodide/triiodide redox couple, a discharge energy density of 167 Wh l −1 is demonstrated with a near-neutral 5.0 M ZnI 2 electrolyte. Nuclear magnetic resonance study and density functional theory-based simulation along with flow test data indicate that the addition of an alcohol (ethanol) induces ligand formation between oxygen on the hydroxyl group and the zinc ions, which expands the stable electrolyte temperature window to from −20 to 50 °C, while ameliorating the zinc dendrite. With the high-energy density and its benign nature free from strong acids and corrosive components, zinc-polyiodide flow battery is a promising candidate for various energy storage applications.