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

Main Aim:
This project will look into the materials used in Aluminium ion and Aluminium air batteries in order to understand how they influence the power output, capacity and recharge ability.

Novelty:
In order to improve the performance of Aluminium ion and Aluminium air batteries, information is needed on the behaviour and the properties of all components including the cathode and the ion-conducting electrolyte.

In metal ion batteries typically the metal is intercalated at the cathode and the electrolyte is used to conduct metal ions or larger complexes containing these ions to the cathode. Similarly for metal air, electrolytes transfer metal ions to the cathode forming metal oxide/peroxide, as well as transferring hydroxide ions to the anode.

Electrolyte:
Electrolytes conduct both anions and cations, forming complexes that can aid or hinder ionic transfer. The electrolyte and its composition have shown large effects on capacity, power and stability as it influences the hydration shell of the type and size of the complex formed e.g. AlCl4- vs Al2Cl-7- complexes behave differently.
Aluminium is a larger ion than lithium with more valent electrons. This means that there is a large change in cathode volume to accommodate the Al3+ ion insertion. This research will look at intercalation of aluminium or anions such as chloride into cathode materials as well as the feasibility of product formation on both electrodes to distribute volume change; e.g. a fully charged cathode that is intercalated with Cl-, which will on discharge move the Cl- to the anode to form AlCl3 while Al3+ moves to the cathode to form Al intercalate. Electrolytes that will be tested include EMIM-Cl/AlCl3 among others that conduct Cl- ions.

Aluminium air batteries could be used in electric vehicles, achieving a theoretical power closer to that of gasoline powered vehicles as well as being a cheaper alternative. The used aluminium can be recycled, reducing the overall waste making the process more sustainable. A potential use for air batteries could be energy storage for renewable sources. Being secondary batteries puts them ahead of the majority of metal-air batteries which are normally non-rechargeable due to unstable electrolytes at higher potentials.

The electrolytes will include EMIM-Cl/AlCl3 which has worked in Al-air batteries but hasn't been tested with different cathodes or additives. Other electrolytes that allow the transfer of OH- ions will also be tested. Additional solvents could also be added to the electrolyte to aid in oxygen reduction/ evolution reaction reversibility.

Cathode:
Ion battery cathode materials will be tested on the basis of the intercalation of cations (aluminium) and anions (e.g. Cl-). The materials that will be studied will include MnO2 because of high power and capacity values obtained in previous research.

The air battery research will focus mainly on cathodes that enable oxygen evolution/reduction reactions and ionic electrolyte materials that are capable of conducting aluminium ions or hydroxide ions. The cathode catalysts to be studied will also include MnO2 as it worked well in ion batteries.