Weakly Solvating Hydrated Eutectic Electrolyte for High-Performance Aluminum-Ion Batteries with Wide Temperature Range

Aqueous aluminum-ion batteries have emerged as a promising alternative to lithium-ion batteries due to their high theoretical capacity, enhanced safety, and low cost. However, their practical application is still hindered by inhomogeneous aluminum deposition, hydrogen evolution reaction, and corrosion during cycling, especially under extreme temperatures and high load conditions. In this study, a hydrated eutectic electrolyte composed of Al(ClO₄)₃·9H₂O and methyl carbamate in a 1:4 molar ratio was designed to improve the stability of aqueous aluminum ion batteries across a wide temperature range. The optimized electrolyte forms a water-deficient, weakly solvated structure, [Al³⁺(MC)₂(H₂O)₂(ClO₄^–)₂]⁺, which kinetically promotes a homogeneous aluminum deposition/stripping behavior. In addition, this electrolyte facilitates the formation of a dense, anion-rich solid electrolyte interface layer on the aluminum anode surface, maintaining long-term anode stability. The Al//Al symmetric cell demonstrated stable cycling for 600 h at a current density of 0.2 mA cm^–2, while the Al//polyaniline (PANI) full battery maintained a specific capacity of 117.7 mAh g^–1 (based on the mass of PANI) after 1100 cycles at 1 A g^–1. Remarkably, this electrolyte also demonstrated excellent cycling stability over a wide temperature range from −15 to 50 °C, offering valuable design principles for aluminum-ion battery applications in large-scale energy storage systems.