Electrochemical Properties and Al Electrodeposition Characteristics of Mixed Chloride–Bromide Molten Salts

To develop molten salt electrolytes for Al electrodeposition, part of AlCl3 in the AlCl3–NaCl–KCl molten salt was replaced with AlBr3 at concentrations of 3, 6, and 9 mol%. The melting point decreased with increasing AlBr3 concentration, reaching a reduction of 20 °C at 9 mol% compared with the chloride-only molten salt. Electrodeposition of Al was conducted using the bromide-containing molten salts at a constant current density of 40 mA cm−2. During electrolysis, both the anode and cathode potentials remained constant for 5000 s. The morphology of the Al deposited on the cathode was observed, and its surface roughness was measured using a laser microscope. The measurements indicated a trend toward reduced surface roughness with increasing AlBr3 concentration. The chloride molten salts containing AlBr3 exhibited lower melting points and improved the surface morphology of the electrodeposits.