Amine-Based Chloroaluminate Ionic Liquids as Electrolytes for Aluminium Batteries: A Synthesis and Evaluation Study

Abstract

Amine-based chloroaluminate electrolytes were developed and assessed in this initial feasibility study, the first investigation of this family for aluminium batteries. Primary, secondary, and tertiary amines with different aliphatic chain lengths were evaluated as precursors. Electrochemical performance was measured by potentiometry, real time viscosity changes were probed with a quartz crystal resonator, and aluminium deposit morphology was characterised by optical and atomic force microscopy. Two systems emerged as promising. Triethylamine/AlCl₃ remained solid without additives up to 313 K. Under polarisation, quartz crystal resonator measurements showed a sharp, reversible decrease in effective viscosity near the electrode, consistent with a localised potential induced solid to liquid transition reported in ionic liquids, and an associated increase in ionic transport. Dodecylamine, AlCl₃ displayed an electrochemical stability window of approximately 1.5 V, comparable to electrolytes already explored for charge storage devices. Both electrolytes exhibited high Faradaic efficiency and redox reversibility, and produced smooth, uniform aluminium deposits. The distinctive features observed here motivate mechanistic studies, long term stability testing, and a systematic survey of amines to develop an optimal solid-state aluminium electrolyte for future devices.