Mixed-Halide Inorganic Molten Salts with Moderately Lower Melting Points for Aluminum Electrodeposition

Chloroaluminate inorganic molten salts are promising Al electrolytes for use in rechargeable batteries, electroplating, and refining because of their low cost, high ionic conductivity, and excellent electrochemical stability. However, their high melting points limit their practical applications. Herein, we report a design strategy to lower the liquidus temperature via partial halide substitution, replacing chloride with bromide, in AlX 3 -NaX (X = Cl or Br) molten salts. The pseudo-binary AlCl 3 -NaBr system exhibited a eutectic temperature of ∼93 °C, which is 15 °C lower than that of the conventional AlCl 3 -NaCl system. Further reduction to 76 °C was achieved in the pseudoternary AlCl 3 -AlBr 3 -NaBr system. Raman spectroscopy and quantum-chemical calculations revealed the formation of mixed-halide Al species, including [AlCl 4– n Br n ] − and [Al 2 Cl 7– m Br m ] −, whose distribution and vibrational signatures were correlated with the bulk halide composition. Although bromide incorporation reduced the ionic conductivity, efficient and reversible Al electrodeposition was achieved at 80–100 °C. These findings highlight the potential of mixed-halide chloroaluminate systems as low-temperature all-inorganic electrolytes. The integration of halide and cation diversity provides a tunable platform for electrolyte design for energy-related Al electrochemical technologies.