Could a new concept replace lithium-ion batteries?

An aluminium battery with twice the energy density as previous versions, and potential for large-scale applications such as storage of solar and wind energy, is being developed by researchers from Chalmers University of Technology, Sweden, and the National Institute of Chemistry, Slovenia. Compared with today’s lithium-ion batteries, the new concept could result in markedly lower production costs and environmental impacts.

The most energy-dense batteries currently available contain lithium. But lithium is expensive, and it is expected to become even more so, with growing demand leading to scarcity. Furthermore, lithium-ion batteries often contain cobalt, which is mined under dangerous working conditions and can fuel conflicts in the countries where it is extracted. Studies at Chalmers are aiming to develop more sustainable energy storage alternatives.

“The material costs and environmental impacts that we envisage from our new concept are much lower than what we see today, making them feasible for large-scale usage, such as solar cell parks or storage of wind energy, for example,” said Patrik Johansson, Professor at the Department of Physics at Chalmers.

“Additionally, our new battery concept has twice the energy density compared with the aluminium batteries that are ‘state of the art’ today.”

Previous designs for aluminium batteries have used aluminium as the anode (the negative electrode) — and graphite as the cathode (the positive electrode). But graphite provides too low an energy content to create battery cells with enough performance to be useful.

In the new concept, graphite has been replaced by an organic, nanostructured cathode made of the carbon-based molecule anthraquinone, which has been extensively developed by Jan Bitenc of the National Institute of Chemistry in Slovenia. The results are published in the journal Energy Storage Materials.

An organic molecule in the cathode material enables storage of positive charge-carriers from the electrolyte — the solution in which ions move between the electrodes — which makes higher energy density possible.

“Because the new cathode material makes it possible to use a more appropriate charge-carrier, the batteries can make better usage of aluminium’s potential,” said Chalmers researcher Niklas Lindahl.

“Now, we are continuing the work by looking for an even better electrolyte. The current version contains chlorine — we want to get rid of that.”

Aluminium batteries are currently not commercially available — even in the research world they are relatively new. The question is, could aluminium batteries eventually replace lithium-ion batteries?

“Of course, we hope that they can,” Johansson said. “But above all, they can be complementary, ensuring that lithium-ion batteries are only used where strictly necessary.

“So far, aluminium batteries are only half as energy dense as lithium-ion batteries, but our long-term goal is to achieve the same energy density.

“There remains work to do with the electrolyte, and with developing better charging mechanisms, but aluminium is in principle a significantly better charge carrier than lithium, since it is multivalent — which means every ion ‘compensates’ for several electrons. Furthermore, the batteries have the potential to be significantly less environmentally harmful,” he said.

Image caption: The battery concept consists of an anode and cathode made of aluminium and an anthraquinone-based organic material. Image credit: © Yen Strandqvist/Chalmers University of Technology.