Transport Numbers of Ions in the Low-Temperature Aluminum Chloride–Triethylamine Hydrochloride Ionic Liquid

Aluminum-ion batteries using the chloroaluminate ionic liquid based on triethylamine hydrochloride (Et3NHCl) as an electrolyte have a high commercial potential, since this electrolyte is cheap and makes it possible to retain all main advantages of this type batteries, such as a high charge/discharge rate, a high Coulomb efficiency, and a high capacitance. However, insufficient attention is given to the transport properties of this electrolyte. The transport numbers of $${\text{E}}{{\text{t}}_{\text{3}}}{\text{N}}{{\text{H}}^ + }$$ , $${\text{AlCl}}_4^ - $$ , and $${\text{A}}{{\text{l}}_2}{\text{Cl}}_7^ - $$ ions were measured by the modified Hittorf method at 373 K in the wide concentration range of AlCl3 molar fractions from 0.50 to 0.66. The external and internal transport numbers of the $${\text{E}}{{\text{t}}_3}{\text{N}}{{\text{H}}^ + }$$ cation are independent of the ion composition in the system and are equal to 0.46 ± 0.06 and 0.98 ± 0.05, respectively. The external transport numbers of the $${\text{AlCl}}_4^ - $$ and $${\text{A}}{{\text{l}}_2}{\text{Cl}}_7^ - $$ anions change according to their molar ratio in the electrolyte, but the sum of the transport numbers of the anions is independent of the electrolyte composition being 0.54 ± 0.06. The conductivities of the basic ILs have been determined for the first time in the concentration range from 0.41 to 0.50. The conductivity of the basic ILs is shown to increase with increasing aluminum chloride content.