Aqueous Electrolyte with Weak Hydrogen Bonds for Four-Electron Zinc-Iodine Battery Operates in a Wide Temperature Range.

In the pursuit of high-performance energy storage systems, four-electron zinc-iodine aqueous batteries (4eZIBs) with successive I - /I 2 /I + redox couples are appealing for their potential to deliver high energy density and resource abundance. However, the susceptibility of positive valence I + to hydrolysis and the instability of Zn plating/stripping in conventional aqueous electrolyte pose significant challenges. In response, we introduce polyethylene glycol (PEG 200) as a co-solvent in 2 m ZnCl 2 aqueous solution to design a wide temperature electrolyte. Through a comprehensive investigation combining spectroscopic characterizations and theoretical simulations, we elucidate that PEG disrupts the intrinsic strong H-bonds of water by global weak PEG-H 2 O interaction, which strengthens the O-H covalent bond of water and intensifies the coordination with Zn 2+ . This synergistic effect substantially reduces water activity to restrain the I + hydrolysis, facilitating I - /I 2 /I + redox kinetics, mitigating I 3 - 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 20000 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. This article is protected by copyright. All rights reserved.