Modeling of Aluminium Deposition from Chloroaluminate Ionic Liquids

A finite-element model of the electrodeposition of aluminium from chloroaluminate ionic liquids is introduced. The purpose of this model is to give an explanation for the reasonable current densities that can be achieved in chloroaluminate ionic liquids despite the fact that the electrochemically active Al2Cl7- complexes are transformed into inactive AlCl4- complexes during the electrodeposition of aluminium. The obtainable current density in the electrodeposition from chloroaluminate ionic liquids strongly depends on the chemical rate constants for establishing the equilibrium Al2Cl7- + Cl- <--> 2AlCl4-. A high current (up to 3000 A m−2) was found for both high and low rate constants whereas a minimum current (200 A m−2) was found for intermediate rate constants due to kinetics and thermodynamics. The model is compared to experiments conducted in the ionic liquid AlCl3-[C2mim]Cl (60/40 mol%) where [C2mim]Cl is 1-ethyl-3-methylimidazolium chloride.