Physicochemical Characterization of AlCl₃–1-Ethyl-3-methylimidazolium Chloride Ionic Liquid Electrolytes for Aluminum Rechargeable Batteries

Abstract

Al-ion batteries technology is receiving growing attention thanks to the high natural abundance of aluminum and to the high energy density that can be obtained with a three-electron redox process. In this work, the physicochemical properties of the room temperature ionic liquid composed of aluminum chloride and 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl) were systematically investigated by varying the molar ratio AlCl3/[EMIm]Cl in the range 1.1–1.7. The combined use of multinuclear (27Al, 13C, 1H) NMR, electrochemical impedance spectroscopy, and thermal analysis allowed us to shed light on the structure–properties relationships of this complex system, also resolving some controversial conclusions of previous literature. We showed that the 1.2 molar ratio is the best compromise between high ionic conductivity and the use of the highly toxic AlCl3. This electrolyte was tested in a standard Al-ion cell and gave promising results even at very high current densities (i > 200 mA g–1).