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Fluoride is better known, at least in the public eye, for its positive correlation with improved dental health than with batteries. However, there is reason to hope that one day it could do double duty and significantly increase the energy density of batteries. Fluoride was first studied in battery chemistry in the 1970s, but could only be used in solid-state batteries, which operate at much higher temperatures than conventional devices.
A breakthrough in fluoride battery chemistry could help accelerate the development of electric vehicles and enable increased adoption of renewable energies. According to a new article published in the journal science, based on work by Caltech, the Jet Propulsion Laboratory, the Honda Research Institute, and the Lawrence Berkeley National Laboratory, there is a way to build batteries with an energy density as high as 8x higher than lithium ion using a new approach that allows fluoride to work in a liquid battery at room temperature. This is a significant scientific achievement whether or not the product is commercialized. So far it was not known whether there was a battery chemistry that would allow a fluoride battery at room temperature.
“Fluoride batteries can have higher energy density, which means they may last longer – up to eight times longer than batteries used today,” said study co-author Robert Grubbs, professor of chemistry at Victor and Elizabeth Atkins of Caltech and winner from the 2005 Nobel Prize in Chemistry. “But fluoride can be difficult to work with, especially because it’s so caustic and reactive.”
An illustration of a battery. In order for batteries to generate electricity, charged atoms called ions (pink and green) move between a negative node (anode) and a positive node (cathode) with the help of a liquid electrolyte solution. Photo credit: Brett Savoie / Purdue University
Using a negatively charged anion as a charge carrier as opposed to a positively charged cation brings its own challenges. In this case, one problem was developing battery chemistry that would work at voltage levels that we actually find useful in modern electronics. In order for fluoride batteries to operate at room temperature, an electrolyte solution called bis (2,2,2-trifluoroethyl) ether, or BTFE, is required. In their test spectrum, the authors have shown that it is possible to build a rechargeable fluorine battery that works at room temperature.
It is not clear what the exact barriers to commercialization are, but there is still a lot to be done before a truly working battery can be assembled. The problem with all battery chemistries is the intrinsic difficulty of finding a solution that reliably stores energy, safely and discharges it in the desired manner, while minimizing events such as thermal runaway. The importance of a new battery chemistry with an 8-fold improvement in energy density compared to lithium-ion cannot be underestimated, but the complexity of battery construction cannot be primarily. For example, the 8-fold improvement in the energy density of fluoride is not very useful if the battery lasts a fraction as long as a lithium-ion cell (at least this type of problem would severely limit actual acceptance). Companies around the world have gone to great lengths to find new alternative battery chemistries and designs, including solid-state batteries, redox flow batteries, lithium-air batteries, and of course, lithium-ion chemistry.
Top Photo Credit: Brett Savoie / Purdue University
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