Imagine not having to charge your phone or laptop for weeks. That is the dream of researchers looking into alternative batteries that go beyond the current lithium-ion versions popular today. Now, in a new study appearing in the journal Science, Chemists at several institutions, including Caltech and the Jet Propulsion Laboratory, which is managed by Caltech for NASA, as well as the Honda Research Institute and Lawrence Berkeley National Laboratory, have a new generation of rechargeable batteries based on fluoride, the negatively charged form, or anion, of the element fluorine.
"Study study co-author Robert Grubbs, Caltech's Victor and Elizabeth Atkins Professor of Chemistry and a winner of the 2005 Nobel Prize in Chemistry. "But fluoride can be challenging to work with, in particular because it's so corrosive and reactive."
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. In the new study, the authors report to the last figure.
"We are still in the early stages of development," says Simon Jones, a chemist at JPL and a corresponding author of the new study.
Batteries drive electrical currents by shuttling charged atoms – or ions – between a positive and negative electrode. This shuttling process proceeds more easily at room temperatures when liquids are involved. In the case of lithium batteries, lithium is shuttled between the electrodes with the help of a liquid solution, or electrolyte.
"Says co-author Thomas Miller, professor of chemistry at Caltech. "You go back and forth between storing the energy and using it."
While lithium ions are positive (called cations), the fluoride ions used in the new study. There are both challenges and benefits to working with batteries.
"For a battery that lasts longer," says Jones, "You can move to greater number of charges." who does research at JPL on power sources needed for spacecraft. "The challenges with this scheme are making the system work at useable voltages." In this new study, we show that we are actually worthy of attention in battery science since we show that fluoride can work at high enough voltages. "
Liquid to liquid electrolyte (2.2.2-trifluoroethyl) ether, or BTFE. This solvent is what keeps the fluoride ion stable so that it can shuttle electrons back and forth in the battery. Jones says his intern at the time, Victoria Davis, who is now studying at the University of North Carolina. While Jones did not have much hope it would succeed, the team decided to try it anyway.
At that point, Jones turned to Miller to understand why the solution worked. Miller and his group ran computer simulations of the reaction and figured out which aspects of BTFE were stabilizing the fluoride. The team was able to tweak the BTFE solution, modifying it with additives to improve its performance and stability.
"We're unlocking a new way of making longer-lasting batteries," says Jones. "Fluoride is making a comeback in batteries."
Materials provided by California Institute of Technology. Original written by Whitney Clavin. Notes: Content may be edited for style and length.