Substituent Effect of Imidazolium Ionic Liquid: A Potential Strategy for High Coulombic Efficiency Al Battery

The chemical structure-effect relationship between imidazolium ion liquid and the properties of electrolyte or Al battery is first completely revealed. First, it is proved that there indeed exsits an interaction between imidazolium cation and chloroaluminate anions (active ions, Al2Cl7- and AlCl4-), blocking their reaction in the anode or positive electrode. Second, by introducing the substituent effect, which could enhance the steric hindrance and change the detailed electronic distribution of imidazolium cations, the intermolecular force between imidazolium cations and chloroaluminate anions is effectively weakened. As a result, the electrodeposition achievement, electrodeposition/electrostripping reversibility of aluminum, and intercalation/deintercalation capacity of AlCl4- in the positive electrode are significantly improved. Therefore, the as-assembled battery with AlCl3/[MPIM]Cl electrolyte shows an similar to 100% CE. This work provides a potential approach on how to enhance the performance of Al battery by designing the ionic liquid structure