Smartphones and laptops of the future may not need to be charged for weeks, thanks to fluoride-based batteries which can last up to eight times longer than those in use today. Researchers, including those from California Institute of Technology and NASA’s Jet Propulsion Laboratory (JPL), found a new way of making rechargeable batteries based on fluoride, the negatively charged form of fluorine.
A study, appearing in the journal Science, looked into alternative batteries that go beyond the current lithium-ion versions popular today. “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,” said Robert Grubbs, a professor at Caltech. “But fluoride can be challenging to work with, in particular because it’s so corrosive and reactive,” Grubbs said. In the 1970s, researchers attempted to create rechargeable fluoride batteries using solid components, but solid-state batteries work only at high temperatures, making them impractical for everyday use.
The new study figured out how to make the fluoride batteries work using liquid components – and liquid batteries easily work at room temperature. “We are still in the early stages of development, but this is the first rechargeable fluoride battery that works at room temperature,” said Simon Jones, a chemist at JPL. Batteries drive electrical currents by shuttling charged atoms – or ions – between a positive and negative electrode. This shuttling process proceeds more easily at room temperature when liquids are involved.
In the case of lithium-ion batteries, lithium is shuttled between the electrodes with the help of a liquid solution, or electrolyte. While lithium ions are positive (called cations), the fluoride ions used in the new study bear a negative charge (and are called anions). There are both challenges and advantages to working with anions in batteries, researchers said. “For a battery that lasts longer, you need to move a greater number of charges. Moving multiply charged metal cations is difficult, but a similar result can be achieved by moving several singly charged anions, which travel with comparative ease,” said Jones.
“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,” he said. The key to making the fluoride batteries work in a liquid rather than a solid state turned out to be an electrolyte liquid called bis (2,2,2-trifluoroethyl) ether, or BTFE, researchers said. This solvent is what helps keep the fluoride ion stable so that it can shuttle electrons back and forth in the battery, they said.