Regulated Hydrated Eutectic Electrolyte Enhancing Interfacial Chemical Stability for Highly Reversible Aqueous Aluminum‐Ion Battery with a Wide Temperature Range of −20 to 60 °C

Abstract The development of aqueous aluminum‐ion batteries (AAIBs) is impeded by pronounced side reactions and hydrogen evolution reaction (HER). Here, an eutectic electrolyte named HEE30 (with an optimal molar ratio of 1:8:1:30 for Al(OTf)3, glycerol (Gly), sodium beta‐glycerophosphate pentahydrate (SG), and H2O) to significantly enhance the reversibility of AAIBs across a wide temperature range from −20 to 60 °C is designed. The combination of molecular dynamics simulations and operando synchrotron Fourier‐transform infrared spectroscopy reveals that the unique eutectic network significantly enhances the hydrogen bonding between Gly and H2O, reduces the solvation interaction of Al3+ with active H2O, thereby lowering the freezing point, extending electrochemical windows and suppressing HER. The X‐ray photoelectron spectroscopy (XPS) and X‐ray diffraction (XRD) tests demonstrate that HEE30 is capable of forming a solid electrolyte interface layer consisting of organic and inorganic components, which effectively inhibits corrosion. Additionally, operando synchrotron XRD and ex situ XPS are employed to investigate the changes in lattice peak width and position of the Prussian white cathode, as well as the reversible storage mechanism during cycling This quantitative design offer immediate advantages for the rational development of low‐cost and safe energy storage batteries, specifically tailored for wide‐temperature operation and durable cycling.