Ternary Ionic Liquid Analogues as Electrolytes for Ambient and Low-Temperature Rechargeable Aluminum Batteries

Rechargeable aluminum (Al) metal batteries are enticing for the coming generation of electrochemical energy storage systems due to the earth abundance, high energy density, inherent safety, and recyclability of Al metal. However, few electrolytes can reversibly electrodeposit Al metal, especially at low temperatures. In this study, Al electroplating and stripping were investigated from 25 °C to -40 °C in mixtures of aluminum chloride (AlCl₃), 1-ethyl-3-methyl-imidazolium chloride ([EMIm]Cl), and urea. The ternary ionic liquid analogue (ILA) consisting of AlCl₃-urea-[EMIm]Cl in a molar ratio of 1.3:0.25:0.75 enabled reversible Al electrodeposition at temperatures as low as -40 °C while exhibiting the highest current density and the lowest overpotential among all of the electrolyte mixtures at 25 °C, including the AlCl₃-[EMIm]Cl binary mixture. The ILA electrolyte was further tested in a rechargeable Al-graphite battery system down to -40 °C. The addition of urea to AlCl₃-[EMIm]Cl binary mixtures can improve the Al electrodeposition, extend the liquid temperature window, and reduce the cost.