Hydride-Enhanced Plating and Stripping of Aluminum from Triflate-based Organic Electrolytes**

Journal article, 2023

In the quest for developing rechargeable aluminum (Al) batteries, reversible Al plating in the absence of active-halide components is considered an immense challenge. For this reason, the choice of electrolyte has been primarily limited to the highly corrosive chloroaluminate systems based on aluminum trichloride (AlCl3). In this work, we demonstrate reversible room-temperature Al plating from an active-halide-free (AHF) organic electrolyte based on aluminum trifluoromethanesulfonate (Al(OTF)3) and lithium aluminum hydride (LiAlH4) in tetrahydrofuran (THF), as well as its AlCl3 counterpart. From insights obtained by Density Functional Theory (DFT) and Fourier-Transform Infrared (FTIR) spectroscopy, ionic speciation in the electrolyte is explored, and mechanisms for the underlying electrochemical processes in the trifluoromethanesulfonate (OTF−)-based electrolytes are proposed. Al plating and stripping were confirmed by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Characterizing the Al deposits from either the OTF−- or the chloride (Cl−)-based electrolytes via depth-profile X-ray Photoelectron Spectroscopy (XPS) analyses, we find that these deposits consist of metallic Al, aluminum oxide (Al2O3), and either aluminum trifluoride (AlF3) or aluminum chloride (AlxCly) contaminants arising from a reaction with the electrolyte components which occurs during the plating process.