Chemists have identified a surprising replacement for the only inherently flammable component of today’s lithium-ion batteries: the electrolyte.
The work, published in 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. The discovery also has the potential to renew consumer confidence in a technology that has attracted significant concern — namely, after recent lithium battery fires in Boeing 787 Dreamliners and Tesla Model S vehicles.
“There is a big demand for these batteries and a huge demand to make them safer,” said Joseph DeSimone at the University of North Carolina at Chapel Hill. “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.”
In the past, researchers have identified alternative non-flammable electrolytes for use in lithium-ion batteries, but these alternatives compromised the properties of the lithium ions. “In addition to being non-flammable, PFPE exhibits very interesting properties such as its ion transport,” said Dominica Wong, a graduate student in DeSimone’s lab who spearheaded the project. “That makes this electrolyte stand apart from previous discoveries.”
The discovery began when DeSimone realised that PFPE, a material that he 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 nothing new; it’s a polymer that has long been used as a heavy-duty lubricant to keep gears in industrial machinery running smoothly.
“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 optimising electrolyte conductivity and improving battery cycling characteristics, which are necessary before the new material can be scaled up for use in commercial batteries, explains Wong. If successful, a commercial battery can also be used in extremely cold environments, such as for aerospace and deep sea naval operations.