Investigation into Non-Aqueous Aluminium-ion Battery Electrolyte and Cathode Materials for Enhanced Power and Capacity

Abstract

Energy storage is one of the most important resources in today’s society. Developing this resource to be more efficient and sustainable is one of the biggest challenges to overcome. For decades, lithium has been at the forefront of energy storage, powering our technology from mobile phones to electric vehicles. The dwindling amount of available lithium left in the world signals that it’s time for the next battery material. Aluminium is not only substantially more abundant across the world, making it cheaper with a lower carbon footprint, but due to its trivalency it possesses a larger capacity than monovalent lithium which could result in smaller, higher capacity and more affordable batteries. This work investigated different electrolyte compositions of aluminium-ion batteries (AIB), a eutectic melt of 1-ethyl-3-methylimidazolium chloride with AlCl3 and its impact on electrochemical stability, anode and cathode performance, and battery coulombic efficiency, degradation, and capacity. The anodic limit of the electrolyte increased with increasing AlCl3 content due to formation of Al2Cl7 - species. Electrolyte degradation studies revealed electrolyte oxidation produces chlorine gas which was detected as HCl. Several carbon-based and metal oxide cathode materials were investigated for AIBs. Cathode potential, mechanism of reaction, coulombic efficiency, specific capacity, and degradation rates were recorded. Charged and discharged cathode material characterisations were carried out using XRD, STM, and Raman spectroscopic techniques. The dominant two mechanisms were found to be chloroaluminate intercalation or electro-adsorption. Cell tests were performed to study the interplay between the Al metal anode, cathodes, and varying electrolyte compositions on charge/discharge. Battery performance was assessed using key performance indicators: specific capacity, specific energy, and coulombic efficiency. Carbonbased materials displayed the greatest performance with graphite giving a specific capacity of 295 mAhg-1 with an energy density of 500 Whkg-1 . A hybrid lithium-aluminium cell using an NMC 811 positive electrode resulted in a capacity of 58 mAhg-1.