Aluminium batteries have emerged as a promising post-lithium energy storage technology that are crucial in tackling the climate crisis. Their high power density (3000W/kg) as well as the high abundance and low cost of aluminium metal make aluminium graphite dual-ion batteries (AGDIBs) an ideal candidate for grid scale storage [1]. Furthermore, the maturity of aluminium processing presents the opportunity for efficient end-of-life recycling [2].

Consisting of an aluminium metal anode, a graphitic carbon cathode and an ionic liquid electrolyte, AGDIBs operate by electrodeposition/dissolution of aluminium at the anode and intercalation/deintercalation of chloroaluminate anions at the cathode during charge/discharge [3]. However, AGDIB development is held back by a lack of fundamental understanding, particularly of the processes at the electrode-electrolyte interfaces. The acidic electrolyte, while non-flammable, poses challenges of corrosion affecting all cell components [4-5] and the processes of corrosion, passivation and dendrite formation at the anode surface are not yet well understood. Specifically, the possible dissolution of native aluminium oxide on the anode is highly contested and limited data is available on the effects of the evolution of this passivating layer on cell performance [6-8].

Motivated by promising work on an optimised graphene nanoplatelet cathode and AlCl₃-trimethylamine hydrochloride electrolyte [9], this work aims to complete understanding of the device by studying the aluminium anode surface and the impact of device configuration. Assembly procedures were explored with a focus on corrosion, material composition, and pressure, revealing the importance of aluminium purity and the limitations of molybdenum in inhibiting corrosion. Detailed surface characterisation was used to investigate anode-electrolyte interface evolution. Time of flight secondary ion mass spectrometry (ToF-SIMS) and x-ray photoelectron spectroscopy (XPS), complimented by optical microscopy and scanning electron microscopy (SEM), were used to probe the composition of an oxide layer and indicate that chlorine and iron are incorporated into the oxide during cycling. Depth profiling was used to deconvolute how the presence of different compounds impacts the formation of other species in this interphase layer.

This work reveals that the evolution of the anode-electrolyte interface is more complex than previously assumed, and how careful consideration of device architecture can play a significant role in optimising this crucial phenomenon and improve device performance.