Understanding aluminium graphite dual-ion batteries: anode-electrolyte interface evolution Anastasia Teck 1 , Huw Shiel 2 , Ifan E.L. Stephens 2 , Mary Ryan 2 , Magda Titirici 1 1 Department of Chemical Engineering, Imperial College London, UK, 2 Department of Materials, Imperial College London, UK Aluminium is a compelling material for post-lithium battery technologies due to its high abundance, low cost, and high theoretical capacity. However, while the trivalent charge of Al 3+ could provide competitive high energy and power densities, its high charge density has significantly limited the number of suitable electrode materials. The aluminium graphite dual-ion battery (AGDIB) relies on an aluminium chloride-based electrolyte which allows de-/intercalation of AlCl 4 - anions into a graphitic carbon cathode, as well as electrodeposition/stripping of aluminium from Al 2 Cl 7 - on a metallic aluminium anode. A major challenge with this cell configuration is the corrosivity of the electrolyte and progress is held back by a lack of fundamental understanding of the stability of all cell components. In particular, little is known about the processes of corrosion, oxide dissolution, and dendrite formation on the anode surface. Motivated by a range of promising results on graphite cathodes and ionic liquid electrolytes, this work aims to further understanding of the device by studying the anode-electrolyte interface. 2-electrode full-cell and 3-electrode half-cell configurations were electrochemically cycled and disassembled for ex-situ analysis. Detailed surface characterisation was then carried out using time of flight secondary ion mass spectrometry (ToF-SIMS) and x-ray photoelectron spectroscopy (XPS), complemented by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), to probe the surface morphology and composition of the native oxide layer. While full-cell post-mortem analysis shows significant corrosion, depth profiling after few cycles indicates notable changes to the native oxide. Both chlorine, from the electrolyte, and iron, from certain cell casings, were found to incorporate into this interphase layer. This work reveals that the evolution of the anode-electrolyte interface is more complex than previously thought, and how careful consideration of device architecture can play a significant role in optimising anode stability to improve device performance.
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© The Author(s), 2021
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