Non-flammable electrode replacement discovered for lithium ion batteries
leThe discovery could help rebuild consumer confidence in lithium-ion battery technology which has been subjected to a good deal of negative publicity following a series of high profile safety mishaps including lithium battery fires on Boeing 787 Dreamliners and Tesla Model S vehicles. The UK’s specialist aviation safety regulator, the Civil Aviation Authority (CAA), has recently expressed concerns "that the huge growth in people carrying lithium batteries on aircraft poses a growing fire risk".
The researchers realized that perfluoropolyether (PFPE), a material they had been researching for the Office of Naval Research to prevent marine life from sticking to the bottom of ships, had a similar chemical structure to a polymeric electrolyte commonly studied for lithium-ion batteries. PFPE is a polymer that has been in use for long time as a heavy-duty lubricant to keep gears in industrial machinery running smoothly.
The work, published in the Feb. 10 issue of the Proceedings of the National Academy of Sciences, paves the way for developing a new generation lithium-ion battery that doesn’t spontaneously combust at high temperatures.
"There is a big demand for these batteries and a huge demand to make them safer," explained DeSimone, Chancellor’s Eminent Professor of Chemistry in UNC’s College of Arts and Sciences and the William R. Kenan Jr. Distinguished Professor of Chemical Engineering at N.C. State University and of Chemistry at UNC. "Researchers have been looking to replace this electrolyte for years, but nobody had ever thought to use this material called perfluoropolyether, or PFPE, as the main electrolyte material in lithium-ion batteries before."
Today’s lithium-ion batteries power everything from mobile devices – phones, tablets and laptops – to jumbo airliners and plug-in electric cars, but an inherently flammable liquid is used as the electrolyte. Lithium ions shuttle through this liquid from one electrode to the other when the battery is being charged. But when the batteries are overcharged, the electrolyte can catch fire and the batteries can spontaneously combust.
Spontaneous combustion is not so much a problem with mobile devices, which are small and replaced frequently, explained Dominica Wong, a graduate student in DeSimone’s lab who spearheaded the project. But when the batteries are scaled up for use in electric cars or planes, their flammability problems are magnified and the consequences can be catastrophic. In the past, researchers have identified alternative nonflammable electrolytes for use in lithium-ion batteries, but these alternatives compromised the properties of the lithium ions.
"In addition to being nonflammable, PFPE exhibits very interesting properties such as its ion transport," said Wong. "That makes this electrolyte stand apart from previous discoveries. When we discovered that we could dissolve lithium salt in this polymer, that’s when we decided to roll with it. Most polymers don’t mix with salts, but this one did and it was nonflammable. It was an unexpected result."
Collaborator Nitash Balsara, faculty senior scientist at Lawrence Berkeley National Laboratory and professor of chemical and biomolecular engineering at the University of California, Berkeley, and his team were then tasked with studying lithium-ion transport within the electrolyte and found compatible electrodes to assemble a battery.
The research team plans to focus on optimizing electrolyte conductivity and improving battery cycling characteristics, which are necessary before the new material can be scaled up for use in commercial batteries. If a commercial battery can be developed also be used in extremely cold environments, such as for aerospace and deep sea naval operations.
Illustration by Melanie Busbee, UNC University Relations
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