Researchers led by chemist Joseph DeSimone at the University of North Carolina at Chapel Hill, in collaboration with Nitash P. Balsara at UC Berkeley, have identified a new class of nonflammable electrolytes based on functionalized perfluoropolyethers (PFPEs) for lithium-ion batteries. In a paper published in the Proceedings of the National Academy of Sciences (PNAS), the team reports that these electrolytes exhibit thermal stability beyond 200 °C and a very high transference number of at least 0.91 (more than double that of conventional electrolytes).
Li/LiNi1/3Co1/3Mn1/3O2 cells made with this electrolyte showed good performance in galvanostatic cycling, confirming the potential as rechargeable lithium batteries with enhanced safety and longevity.
Commercial Lithium-ion batteries usually contain an electrolyte that is dissolved in flammable organic solvents; damage to the battery from a variety of causes can result in fire, sometimes with catastrophic effect. A number of efforts are being made to develop non-flammable electrolyte alternatives (e.g., earlier post.)
In the past, researchers have identified alternative nonflammable electrolytes for use in lithium-ion batteries, but these alternatives compromised the performance of the batteries, the researchers said.
In addition to being nonflammable, PFPE exhibits very interesting properties such as its ion transport. That makes this electrolyte stand apart from previous discoveries.—Dominica Wong, lead author
The study may represent a significant step toward a lithium-ion battery with improved safety and pave the way for the development of new electrolytes that can address the persisting challenges of current battery technologies, the authors suggest.
There is a big demand for these [Li-ion] batteries and a huge demand to make them safer. 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.—Prof. Joseph DeSimone
The discovery began when DeSimone realized 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.
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. If successful, a commercial battery can also be used in extremely cold environments, such as for aerospace and deep sea naval operations.
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.—Dominca Wong
Dominica H. C. Wong, Jacob L. Thelen, Yanbao Fu, Didier Devaux, Ashish A. Pandya, Vincent S. Battaglia, Nitash P. Balsara, and Joseph M. DeSimone (2014) “Nonflammable perfluoropolyether-based electrolytes for lithium batteries,” PNAS doi: 10.1073/pnas.1314615111