Aluminium metal batteries are a compelling post-lithium technology to diversify the battery market. In addition to its high theoretical capacity, aluminium is the most abundant metal in the earth’s crust and its processing is well established, leading to low cost and promising recyclability. Aluminium graphite dual-ion batteries (AGDIBs) were first developed in 2015 and have since gained attention for their affordable graphite electrodes, non-flammable ionic liquid electrolytes, and high power density. The AGDIB utilises an aluminium chloride room-temperature ionic liquid to allow de-/intercalation of AlCl₄^- anions into the graphitic carbon cathode and electrodeposition/stripping of aluminium from Al₂C₇^- anions at the metallic aluminium anode. However, a significant challenge to this configuration is limited understanding of the stability of cell components in the corrosive electrolyte. Particularly little is known about the fundamental processes of corrosion and interphase formation at the anode-electrolyte interface and their effects on aluminium electrodeposition.  

Building on promising studies of graphite cathode and chloroaluminate electrolyte materials, this work aims to further fundamental understanding of the device by in situ and ex situ studies of the anode surface during battery operation. 2-electrode full cell configurations were galvanostatically cycled to different potentials and disassembled anodes were washed in dimethyl carbonate for ex situ analysis. A systematic study of the anode morphology by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and atomic force microscopy (AFM) revealed the growth of concentric ring features as a result of side-reactions causing heterogeneous corrosion and electrodeposition. Solid electrolyte interphase formation on these porous features was then studied using X-ray photoelectron spectroscopy (XPS) and cross-sectional transmission electron microscopy (TEM) to reveal significant insertion of chlorine and some incorporation of iron species into the existing native oxide layer. This phenomenon was further studied by operando Near Edge X-ray Absorption Fine Structure spectroscopy (NEXAFS) in a custom cell to achieve realistic testing conditions.

This work shows that the anode-electrolyte interface is more complex than often assumed, with heterogeneous deposition impacting cell stability, as well as solid electrolyte interphase formation affecting diffusion for deposition and corrosion. Better understanding of these phenomena is key for targeted modifications of the system to improve the electrolyte and protect the anode surface to enable longer shelf and cycle life of aluminium batteries.