New Cathodes for Rechargeable Aluminium-ion Batteries

S. Divya, J. Johnston, T. Nann
Victoria University of Wellington,
New Zealand

Keywords: aluminium-ion battery, ionic liquid, cathodes, chloroaluminates

Summary:

Lithium-ion batteries (LIBs) are a popular battery-choice for most applications. However, future battery demand will place increasing pressure on lithium and cobalt reserves and supply lines in the medium and long term. Moreover, the electrolyte used in LIBs is flammable, which is a safety issue that has to be managed. Any mechanical damage to the cell might result in short circuits or thermal runaway reactions, sometimes leading to an explosion! High abundance and easy accessibility of aluminium resources enable aluminium-ion batteries (AIBs), together with their electrochemical characteristics and performance, offer the opportunity to become an ideal alternative. A multivalent ion insertion is feasible, which can help in achieving higher energy density than LIBs. Non-aqueous AIBs use a non-flammable ionic liquid as their electrolyte, making them safer than LIBs in this regard. The most common electrolyte for AIBs is currently the ionic liquid 1-ethyl-3-methyl imidazolium chloride ([EMIm]Cl) mixed with aluminium trichloride (AlCl3) where a chloroaluminate ion is the active charge-carrying species, although other alternatives are under investigation. Figure 1 shows a schematic illustration of an aluminium-ion battery using pure aluminium foil as the anode and EMImCl/ AlCl3 mix as the electrolyte. Our research on AIBs is at an early stage and current work focuses mainly on cathode materials. We tested different materials as cathodes for rechargeable AIBs. We expected that two-dimensional (2D) layered materials might be suitable as active cathode materials since they display similar properties as graphite. They allow the intercalation of chloroaluminate ions and are electrically conductive. We focused on 2D layered materials such as transition metal dichalcogenides (MoX2, here X = S, Se or Te, WS2, etc.), natural carbon-based materials (activated carbon from human hair, hemp fibers), and a few nitride compounds with the aim to achieve an AIB with a superior performance over those previously reported. Our results have shown that some of the cathode materials we have developed, desirably have high stability and long cycle life, and also outperform many cathodes existing in current AIB literature.