Aqueous Electrolyte With Weak Hydrogen Bonds for Four‐Electron Zinc–Iodine Battery Operates in a Wide Temperature Range

Abstract

In the pursuit of high-performance energy storage systems, four-electron zinc-iodine aqueous batteries (4eZIBs) with successive I^-/I₂/I⁺ redox couples are appealing for their potential to deliver high energy density and resource abundance. However, susceptibility of positive valence I⁺ to hydrolysis and instability of Zn plating/stripping in conventional aqueous electrolyte pose significant challenges. In response, polyethylene glycol (PEG 200) is introduced as co-solvent in 2 m ZnCl₂ aqueous solution to design a wide temperature electrolyte. Through a comprehensive investigation combining spectroscopic characterizations and theoretical simulations, it is elucidated that PEG disrupts the intrinsic strong H-bonds of water by global weak PEG-H₂O interaction, which strengthens the O─H covalent bond of water and intensifies the coordination with Zn²⁺. This synergistic effect substantially reduces water activity to restrain the I⁺ hydrolysis, facilitating I^-/I₂/I⁺ redox kinetics, mitigating I₃ ^- formation and smoothening Zn deposition. The 4eZIBs in the optimized hybrid electrolyte not only deliver superior cyclability with a low fading rate of 0.0009% per cycle over 20 000 cycles and a close-to-unit coulombic efficiency but also exhibit stable performance in a wide temperature range from 40 °C to -40 °C. This study offers valuable insights into the rational design of electrolytes for 4eZIBs.