Optimization of an Artificial Solid Electrolyte Interphase Formed on an Aluminum Anode and Its Application in Rechargeable Aqueous Aluminum Batteries

Electrochemical cells that incorporate aluminum (Al) as the active material have become increasingly popular due to the advantages of high energy density, cost-effectiveness, and superior safety features. Despite the progress made by research groups in developing rechargeable Al//MxOy (M = Mn, V, etc.) cells using an aqueous Al trifluoromethanesulfonate-based electrolyte, the reactions occurring at the Al anode are still not fully understood. In this study, we explore the artificial solid electrolyte interphase (ASEI) on the Al anode by soaking it in AlCl3/urea ionic liquid. Surprisingly, our findings reveal that the ASEI actually promotes the corrosion of Al by providing chloride anions rather than facilitating the transport of Al3+ ions during charge/discharge cycles. Importantly, the ASEI significantly enhances the cycling stability and activity of Al cells. The primary reactions occurring at the Al anode during the charge/discharge cycle were determined to be irreversible oxidation and gas evolution. Furthermore, we demonstrate the successful realization of urea-treated Al (UTAl)//AlxMnO2 cells (discharge operating voltage of ∼1.45 V and specific capacity of 280 mAh/g), providing a platform to investigate the underlying mechanisms of these cells further. Overall, our work highlights the importance of ASEI in controlling the corrosion of Al in aqueous electrolytes, emphasizing the need for the further development of electrolytic materials that facilitate the transport of Al3+ ions in rechargeable Al batteries.