Aluminum anodes can provide the US with a secondary battery for high energy density applications, such as stationary energy storage or batteries for transportation needs. Aluminum is the most abundant metal in the earth's crust and can safely been stored and exposed to standard atmospheres (unlike lithium metal), and has an energy density surpassing zinc and competitive with lithium. Since aluminum cannot be easily electrodeposited from aqueous solutions due to breakdown of water, it is important to use non-aqueous solution such as ionic liquid which are room-temperature molten salts. To develop safer batteries based on aluminum metal anodes, this work uses ionic liquids as battery electrolytes, due to their low vapor pressures, non-flammability, and high electrical conductivities.
The aluminum electrodeposition on copper current collectors from two different types of ionic liquids, 1-butyl-3-methyl imidazolium chloride and 1-ethyl-3-methyl imidazolium chloride, has been studied. Under galvanostatic electrodeposition from BMIM-chloraluminate melts, it was found that bright, adherent aluminum was obtained in the range of 0.2 - 1 mA/cm2. Above 1mA/cm2, mixed depositions results with non-adherent complexed organic material were obtained. Potentiostatic deposition resulted in bright, smooth and adherent deposits in the range of -0.05 V to -0.4 V vs Al. Beyond -0.4 V, the freshly deposited Al reacts further resulting into non-adherent complexed material.
Upon cycling in the appropriate current density range, current efficiencies of 50-70% were observed. Upon repeated cycling, this efficiency was observed to 100 cycles and beyond. Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) analysis was used to characterize the deposits. The SEM/EDX analysis indicated the deposits were pure aluminum.
These results were repeated with EMIM-based electrolyte melts, providing insight into the effect of ionic liquid cation on battery anode performance.