Most of our devices nowadays use lithium-ion batteries. Their development is a technological marvel, but now that they are common we focus more on the negative than the positive. And the biggest negative is the need to recharge them at least daily. Now imagine a battery that would only need to be recharged once a week.
That dream is closer to reality now thanks to researchers from various institutions. Their focus has been on fluoride, which can pack a lot more charge in. Now, they have managed to build the first rechargeable fluoride liquid battery that works at room temperature. The breakthrough is reported in the journal Science.
Previous research has struggled with fluoride for several reasons. In the 1970s, solid-state fluoride batteries were developed but they require temperatures so high that they can’t be used in everyday devices. Still, the promise was exciting enough for scientists to keep investigating them.
“Fluoride batteries can have a higher energy density, which means that they may last longer – up to eight times longer than batteries in use today,” co-author Professor Robert Grubbs, Caltech chemist and a winner of the 2005 Nobel Prize in Chemistry, said in a statement. “But fluoride can be challenging to work with, in particular because it’s so corrosive and reactive.”
Batteries work by moving a certain number of charged atoms in a particular direction, accumulating energy and then releasing it as those charges move between electrodes in a liquid solution known as an electrolyte. Lithium ions are positive and known as cations, the fluoride ions are negative and known as anions.
Lead author of the study, Victoria Davis, who is now studying at the University of North Carolina, was able to find a good solvent to use with fluoride. This electrolyte is known as bis(2,2,2-trifluoroethyl)ether, or BTFE, and has successfully managed to keep fluoride ions stable, leading to the successful prototype.
“For a battery that lasts longer, you need to move a greater number of charges,” co-author Simon Jones, from the Jet Propulsion Laboratory. “Moving multiple charged metal cations is difficult, but a similar result can be achieved by moving several singly charged anions, which travel with comparative ease. The challenges with this scheme are making the system work at useable voltages. In this new study, we demonstrate that anions are indeed worthy of attention in battery science since we show that fluoride can work at high enough voltages.”
The team has also employed simulations to tweak the electrolyte and improve both performance and stability. It’s still early days but fluoride batteries could soon become commonplace.