The Ag electrode used as a working electrode was made of a special mixed bonded silver paste (9912-A) applied on ceramic alumina with a thickness of 25 μm. An SEM image showing the microstructure of screen-printed Ag on ceramic electrode is provided in fig. S4B. Al was electrodeposited galvanostatically at a current density of 20 mA cm−2 for 30 min from an ionic liquid mixture of 60 mole percent of AlCl3 and 40% 1-ethyl 3-methylimidazolium chloride ([EMIm]Cl; BASF) (43), ensuring Lewis acidity. An ionic liquid was dried under vacuum with intensive stirring for 12 to 24 hours at temperatures that were kept in the range of 85° to 95°C to remove residual moisture. The content of moisture in the ionic liquid was checked by Karl Fischer coulometric titration showing water content before and after drying under vacuum of 300 and 10 ppm, respectively. After drying, the ionic liquid was transferred to an argon-filled glove box (LABstar MBraun) with O2 and H2O contents below 1 ppm where electrodeposition experiments were carried out. It should be emphasized that the ionic liquid used for electrodeposition was highly hygroscopic, and therefore, some residual water content was inevitable. The current densities of −10 and −20 mAcm−2 were selected because at lower values, longer deposition times are needed, which increased the risk of contamination, whereas at the higher current densities, the achieved layers were mechanically unstable. The preparation of the bath, the cyclic voltammetry measurements, the chronopotentiometric measurements, and the electrodeposition experiments were carried out inside of a glove box filled with argon at a temperature of 85°C using a VoltaLab potentiostat, PGZ 301. A pure Al sheet (99.999%, Goodfellow) was immersed into the ionic liquid and used as anode in constant current deposition experiments. The distance between the cathode and anode was about 2 cm. The electrolyte was stirred at a constant rate of 300 rpm. The cleaning procedure of the samples after electrodeposition and removal from the glove box includes washing with acetone, rinsing with deionized water, and drying with compressed air. The thickness of the obtained Al layer was around 10 μm.