Effect of Operating Temperature and Additives to Chloroaluminate Ionic Liquid Electrolyte on Current Efficiency and Surface Morphology of Al Electrodeposit (Supporting Information)

To investigate the feasibility of the electrorefining process for aluminum (Al) upgrade recycling, Al electrodeposition employing an ionic liquid consisting of anhydrous aluminum chloride (AlCl₃) and 1-ethyl-3-methylimidazolium chloride (EMIC) was conducted. The effects of the operating temperature on the current efficiency, specific energy consumption, deposit properties, and deposition rate were investigated using the AlCl₃-EMIC bath containing 1,10-phenanthroline anhydride (OP) as an additive at the current density of 100 mA cm⁻². A constant-current electrodeposition showed that the specific energy consumption decreased to 5605 kWh t⁻¹ at 80 °C with increasing the operating temperature in the OP-added bath and the current efficiency was over 90 % at the operating temperatures of 60–80 °C, but decreased to below 90 % at 90–100 °C. The cross-sectional ultra-low accelerating voltage scanning electron microscope (ULV-SEM) images showed the smoothness of the deposit obtained from the OP-added bath at 70 °C, but not at 90 °C. The XRD patterns of the Al deposits obtained from the OP-added bath showed a preferential orientation to the {100} plane at 60–80 °C, but almost no preferential orientation at 90–100 °C. It has been revealed that the improvement in the specific energy consumption requires an increase in the operating temperature, and that the surface roughness of the Al deposit must be improved by preferentially orienting the {100} plane in the texture to prevent any Al deposit from dropping out in order to improve the current efficiency at the cathode, which implies Al recovery.