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, 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 & horbar;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-/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 20 000 cycles and a close-to-unit coulombic efficiency but also exhibit stable performance in a wide temperature range from 40 degrees C to -40 degrees C. This study offers valuable insights into the rational design of electrolytes for 4eZIBs.