Synergistic Effects of Electrolyte Additives in a Dual‐Salt System for High‐Performance Four Electron Aqueous Zinc–Iodine Batteries Across a Wide Temperature Range

Four-electron aqueous zinc-iodine batteries (4eAZIBs) with the successful I^-/I⁰/I⁺ redox couples have emerged as a promising alternative for large-scale energy storage due to their high energy density. However, the practical application of these batteries, particularly in harsh environments, is hindered by the poor reversibility of Zn plating/stripping processes and the instability of I⁺ species in conventional aqueous electrolytes. Here, we design a multi-component hybrid electrolyte composed of Zn(ClO₄)₂, ZnCl₂, glycerol (Gly), and polyvinyl alcohol (PVA) to enable highly reversible operation of 4eAZIBs across a wide temperature range. Theoretical calculations, molecular dynamics simulations, and spectral analyses reveal that Gly and PVA synergistically modify the intrinsic hydrogen bond network and effectively reduce the content of active water molecules, thereby enhancing the plating/stripping behavior of Zn²⁺, suppressing the hydrolysis of I⁺, and lowering the freezing point of the electrolyte. Moreover, the PVA-containing dual-salt system reduces the Gibbs free energy of the I^-/I⁰/I⁺ reaction, facilitating enhanced stability of the 4eAZIBs even under low chloride concentrations. Consequently, the Zn||I₂ full cells using this system exhibit a remarkable lifespan of 15 000 cycles with a capacity attenuation of 0.15% per hundred cycles, and along with excellent performance over a wide temperature range from -50 to 40 °C.