Non-flammable lithium-ion batteries may be the outcome of research on a material preventing marine life sticking to ships.
A team led by chemist Professor Joseph DeSimone at the University of North Carolina (UNC), USA, have identified a surprising replacement for the only inherently flammable component of today's lithium-ion batteries: the electrolyte.
But the researchers say their discovery, detailed in journal The Proceedings of the National Academy of Sciences yesterday, 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," said DeSimone. "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."
Lithium-ion batteries’ high energy density and low loss of charge mean they are often the first choice to power everything from phones, tablets and laptops to jumbo airliners and plug-in electric cars, but an inherently flammable liquid is used as the electrolyte – a lithium salt in an organic solvent.
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, explains 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."
PFPE is a polymer that has long been used as a heavy-duty lubricant to keep gears in industrial machinery running smoothly that DeSimone had been researching for the Office of Naval Research to prevent marine life from sticking to the bottom of ships.
The discovery began when DeSimone realized that PFPE had a similar chemical structure to a polymeric electrolyte commonly studied for lithium-ion batteries.
"When we discovered that we could dissolve lithium salt in this polymer, that's when we decided to roll with it," said Wong. "Most polymers don't mix with salts, but this one did and it was non-flammable. 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 assembly a battery.
Going forward, the team will 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, said Wong.
If successful, a commercial battery can also be used in extremely cold environments, such as for aerospace and deep sea naval operations.
"This is a really good starting point for us to go in a lot of different directions and bridge the gap between academic research and industrial scale-up," said Wong. "But the best part was the interdisciplinary collaboration; having the opportunity to work on scientific problems with researchers with different backgrounds and expertise."