Demand for lithium batteries is growing as we are increasingly leaning towards products that use cleaner forms of energy, such as electric vehicles. However, the materials used in these batteries come with their own set of environmental problems.
Lithium mining can cause toxic chemicals to leak into the surrounding area, leading to air, water and soil contamination, all of which can be hugely detrimental to the local ecosystems. Cobalt, another product used in conventional batteries, can take a high toll on the health of those who mine it and the environment.
But attempts to create a more environmentally-friendly alternative have not always been successful. Previous designs that use aluminum for the negative electrode (the anode) have used graphite for the positive electrode (the cathode). The problem with this, the researchers say, is that graphite has too low an energy content to make viable batteries. To put it bluntly, they are just not efficient enough to be of any interest to consumers.
To overcome this particular dilemma, researchers from Chalmers University of Technology, in Sweden, and the National Institute of Chemistry, in Slovenia, have replaced the graphite cathode with one made of an organic, carbon-based molecule—called anthraquinone. This allows for the storage of positive charge-carriers from the electrolyte (i.e. a liquid or gel that contains ions) carried by the battery and thus, a higher energy density.
“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 Niklas Lindahl, a researcher from Chalmers.
But the team are still hoping to do one better and plan to work out ways to improve the electrolyte.
“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,” Lindahl added.
The batteries come with the added economic benefit of lower production costs than the lithium batteries we use today.
“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,” explained 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.”
So, should we expect lithium batteries to be binned in favor of aluminum any time in the near future?
“Of course, we hope that they can,” said Johansson. “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.”
