Ionic Liquid Electrolytes for Rechargeable Aluminum Batteries

Abstract

Rechargeable aluminum battery is considered as a promising battery system used in energy storage devices, due to its abundant natural resources and high capacity. However, fabrication of this battery working at room temperature didn’t succeed until haloaluminate contained ionic liquids were used as electrolytes. Therefore, electrolytes are expected to have a great effect on performance of rechargeable aluminum battery. For ionic liquid electrolytes, anions play a major role in its electrochemical properties. Anion-effect of haloaluminate contained ionic liquids prepared with different halogenated imidazole salt and AlCl 3 /imidazolium chloride mole ratio are studied. Electrochemical window is found narrowing with reducibility of halide ion and AlCl 3 mole fraction. When used as electrolyte in rechargeable aluminum battery with V 2 O 5 nanowire cathode, AlCl 3 /[BMIM]Cl ionic liquid with the mole ration of 1.1:1 shows the best performance. The as-assembled cell exhibits a high discharge voltage platform (1 V) and capacity (288 mAh/g) at the first cycle. Concentration of Al 2 Cl 7 - is considered as a key factor in chloroaluminate ionic liquids when used as electrolyte. A slightly corrosion is found on the surface of Al metal foil immerged in acid AlCl 3 /[BMIM]Cl ionic liquids after 24 h. It means this kind of ionic liquids may help to remove the oxide film on Al metal foil. The oxide film is considered as a mainly hinder to performance of aluminum battery. Performance of battery using ionic liquid with other anions (such as BF 4 - , PF 6 - and CF 3 SO 3 - ) has not been reported, which is probably due to the dense Al 2 O 3 film formed on surface of Al anode. It prevents the oxidation of Al in discharge process of battery and causes a failure. Figure 1