Modulating Solvation Structure and Desolvation Dynamics of Hydrate Eutectic Electrolytes for Cost-Effectiveness, Ultralong Cyclability, and High Reversibility of Zn–Al Alloy Anode

Aqueous aluminum-ion batteries (AAIBs) hold significant promise for scalable grid energy storage because aluminum (Al) anodes offer advantages such as abundant reserves in the earth’s crust, low cost, high capacity, and environmental friendliness. However, the widespread adoption of AAIBs is currently limited by aluminum trifluoromethanesulfonate (Al(TOF)3) salt-based aqueous electrolytes, which are both expensive and environmentally problematic. To address this limitation, we introduce a novel hydrated eutectic electrolyte (HEE) composed of hydrated aluminum sulfate (Al2(SO4)3 · 18H2O) as the solute and ethylene glycol (EG) as the solvent, notably costing approximately 1/15th the price of Al(TOF)3. This HEE leverages strong coordination between EG molecules and Al3+ ions, facilitated by hydrogen bonding and solvation effects, to promote more uniform aluminum deposition and suppress dendrite formation on zinc substrates compared to conventional aqueous Al2(SO4)3 electrolytes. Consequently, the formation of anionic/cationic complex species reduces interfacial impedance, enabling a highly reversible aluminum plating/stripping process characterized by low overpotentials (∼130 mV) and an extended cycle life of up to 2000 h. Furthermore, when incorporated into a full cell using a Zn–Al anode and a phosphorus-doped V2O5 (P–V2O5) cathode, this HEE demonstrates excellent rate capability and cycling stability. This work provides new opportunities for constructing high-performance and low-cost AAIBs for practical applications.