Pyrrolic‐Nitrogen Chemistry in 1‐(2‐hydroxyethyl)imidazole Electrolyte Additives toward a 50,000‐Cycle‐Life Aqueous Zinc‐Iodine Battery

Abstract

Rechargeable aqueous zinc iodine (Zn-I₂) batteries offer benefits such as low cost and high safety. Nevertheless, their commercial application is hindered by hydrogen evolution reaction (HER) and polyiodide shuttle, which result in a short lifespan. In this study, 1-(2-hydroxyethyl)imidazole (HEI) organic molecules featuring pyrrole-N groups are introduced as dually-functional electrolyte additives to simultaneously stabilize Zn anode and confine polyiodide through ion-dipole interactions. The pyrrole-N groups in HEI can preserve the interfacial pH equilibrium at Zn anode by reversibly capturing H⁺ ions and dynamically neutralizing OH^- ions, thereby suppressing the HER. Notably, the H₂ evolution rate at the Zn anode is reduced to a mere 2.20 μmol h^-1 cm^-2. Furthermore, the pyrrole-N moieties in HEI effectively curtail the polyiodide shuttle at I₂ cathode, which show adsorption energies of -0.174 eV for I₂, -0.521 eV for I₃ ^-, and -0.768 eV for I^-, as indicated by density functional theory calculations. Electrochemical testing demonstrates that the Zn//Zn symmetric cell maintains stable cycling for up to 4,200 hours at 1 mA cm^-2. Most strikingly, at a high I₂ mass loading of 9.7 mg cm^-2, the Zn-I₂ battery achieves an extraordinary cycle life of 50,000 cycles.