Research into a practical application for aluminium in rechargeable batteries is starting to bear fruit, with scientists having built a functional aluminium-ion prototype. Although a young technology, it is hoped that the use of aluminium in rechargeable batteries could be the next step in the commercial and industrial sectors.
The two current drawbacks of the aluminium cell when compared to its lithium-ion counterpart are increased expansion and contraction of the reactive material, which represents a significant challenge for even the most experienced battery pack manufacturer; and a comparative lack of power.
Batteries of the Future?
The research team at Stanford University paired an aluminium anode with a positive cathode made of graphite in a successful test battery. The thin layers of atoms in graphite makes it an ideal material for this purpose. During discharge, aluminium travels from the anode, reacting in ionic form at the cathode. When the battery recharges this process is reversed, with metallic aluminium returning to the cell’s negative anode.
The salt solution chosen as the battery’s electrolyte is more stable at room temperature than that of typical lithium-ion cells. This solution is also adept at getting in between the flat sheets of atoms inside the graphite cathode to produce a potent reaction. The combination of aluminium, graphite and salt electrolyte results in a battery that is safe, inexpensive to produce and performs both charge and discharge at good rates over more than 7,500 complete cycles.
Image credits: Royal Society of Chemistry
However, this collection of materials have drawbacks that must be addressed if the aluminium-ion battery is to have a future. Ungainly expansion and contraction of the cell occurs when ions are forced between the many slender sheets of graphite in the cathode.
Such rapid reactions, though essential for the battery’s high rate of charge, are a headache for a battery pack manufacturer in creating a pack that can accommodate a fluctuating cell size.
Additionally, although the aluminium-ion cell can fully recharge in under a minute and fares well in comparison with its lithium counterpart on safety and durability, the prototype is only able to deliver two volts of power, around fifty per cent of a lithium-ion battery’s typical output.
To increase the aluminium-ion cell’s output it is likely that the cathode material would have to be altered, with the possible loss of some or all of the prototype’s advantages over lithium-ion, such as durability, safety and an enviable recharge rate.