Understanding the Reversible Electrodeposition of Al in Low-Cost Room Temperature Molten Salts

Al-based batteries are considered an attractive alternative to Li metal due the use of Al as anode with lower cost, reactivity and larger abundance compared Li. Despite aforementioned attributes, few electrolytes permit reversible electrodeposition at room temperature. Thus, for last 30 years, expensive imidazolium-based ionic liquids have dominated field. Even though extensive research has been conducted on liquids, a systematic study that sheds light structural requirements, physicochemical transport properties required enable high reversibility not conducted. Here, we investigated two ammonium-based systems show comparable Coulombic efficiencies up 99.1% over 1000 cycles (1 mAh/cm 2 , 4 mA/cm ). We reveal in ammonium- imidazolium- based is achieved when critical ratio solvation species (AlCl - Cl 7 ) obtained, where Lewis’s acidity beneficial interfacial reactions continuously etch O 3 resistive layer uniform current distribution attained anode. Insights were obtained via construction phase diagrams, 27 quantitative NMR, considerations, chemical analyses, electrochemical measurements. The findings yield molecular-level understanding room-temperature molten salts five times cheaper than commonly used electrolytes. fundamental gained structural, can guide engineering approaches other electrolyte batteries. Furthermore, development low-cost, high-rate capability long-term stability accelerate high-capacity cathodes leading higher energy densities relevant electric vehicles.