Abstract
Lithium-ion batteries are currently the dominating battery technology in the market, but the increased demand for batteries [1] combined with the safety requirements, materials availability and sustainability evaluations, makes it important to investigate new battery approaches. Aluminium-Carbon (Al-C) batteries are suggested as candidates using cheap, safe and more abundant electrode materials, but do introduce new challenges. In an Al-C battery, the aluminium has the role as the anode and carbon as the cathode; during charging anions intercalate into the carbon structure, while the aluminium deposit on the anode [2]. Research have focused on the electrolytes [3], and several types of carbon cathode materials have also been investigated [4]. The aluminium anode has been given less attention, despite issues like presence of an insulating oxide film, dendrite formation, volume expansion, and self-corrosion [5]. Both surface treatment and alloying could change positively the surface properties of the aluminium anode [6]. An established non-aqueous electrolyte that is shown to function well for Al-C batteries is based on a mixture of AlCl 3 dissolved in 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl), typically in molar composition 1:1 to 2:1 AlCl 3 :[EMIm]Cl. In this work, two different compositions of this ionic liquid electrolyte have been investigated, with molar ratio 1.3:1 and 2:1, with a goal of understanding the differences with respect to the negative aluminium electrode in an Al-C battery. Two types of electrodeposition experiments have been conducted. In the first setup, the aluminium deposition occurred on constant current density on Al or Mo wires using a 3-electrode setup. In the second setup, a battery type PAT-Cell (EL-CELL®) with an Al reference ring was used in a symmetric setup to cycle aluminium electrodes of different alloy quality for a minimum of 50 times or 100 hours. The current density used was in the 0.1-0.5 mA/cm 2 range, with a given capacity in the range of 0.1-1 mAh/cm 2 . Aluminium wires and electrodes were cleaned using dimethyl carbonate before investing them using Scanning Electrode Microscopy. The 1.3:1 ratio appeared stable under all conditions, giving repeatable and almost non-changing potential measurements for both deposition and dissolution for 50 cycles, with only a small increase in potential values using 0.1 and 0.5 mA/cm 2 . The 2:1 electrolyte behaved somewhat differently when using high current density, the initial cycles typically varying a lot prior to the potential stabilization, and a large difference in potential when varying the current density was also observed. Additionally, under certain conditions using an aluminium purity of 99 %, additional signals on both deposition and dissolution were measured after the initial cycles using the 2:1 electrolyte, indicating additional electrochemical reactions (see associated figure). This could be caused by the presence of Fe, an impurity confirmed by SEM-EDS for this aluminium purity, which may dissolve and deposit after a certain amount of time. Although the 2:1 electrolyte appeared to be harsher on the proposed aluminium reaction with higher potentials and possible new reactions, independently of the parameters chosen the reactions occurring on the aluminium electrodes appeared to stabilize over time, indicating a good applicability in the proposed Al-C battery. Acknowledgements This project has received funding from The Research Council of Norway: Contract number 331964. Partners in the project are NTNU, SINTEF, Vianode, Beyonder and Equinor ASA. References [1] B. Jones et al.(2023) The World Economy 46 2-26 [2] M-C. Lin et al. (2015) Nature 520, 324-328 [3] K.V. Kravchyk & M.V. Kovalenko (2020), Communications Chemistry 3, 120 [4] Y.Ru et al. (2019), J. Mater. Chem. A 7, 14391-14418 [5] M. Jiang et al. (2022), Adv. Mater . 34, 2102026 [6] G.Razaz et al. (2024) ACS Appl. Mater. Interfaces , 16, 65725−65736 Figure 1