Ann Arbor-based Elegus Technologies expects to begin production of a new battery technology that company officials say will prevent the kind of fires that grounded a Boeing 787 airline in 2013.
Under development by Nicholas Kotov at the University of Michigan, the battery’s membrane is made with nanofibers extracted from Kevlar, the tough material in bulletproof vests. Kotov says Kevlar’s heat resistance could also lead to safer batteries as the membrane stands a better chance of surviving a fire than most membranes currently in use.
“Unlike other ultra strong materials such as carbon nanotubes, Kevlar is an insulator,” says Kotov, a professor of engineering. “This property is perfect for separators that need to prevent shorting between two electrodes.”
He says 30 companies have requested samples of the material and production could start next year.
Lithium-ion batteries work by shuttling lithium ions from one electrode to the other. This creates a charge imbalance, and since electrons can’t go through the membrane between the electrodes, they go through a circuit instead.
But if the holes in the membrane are too big, the lithium atoms can build upon themselves, forming fern-like structures that can poke through the membrane. If they reach the other electrode, the electrons have a path within the battery, shorting out the circuit. This is how the battery fires on the Boeing 787 are thought to have started Kotov says.
While the widths of pores in other membranes are a few hundred nanometers, or a few hundred-thousandths of a centimeter, the pores in the membrane developed by Kotov are 15 to 20 nanometers across. They are large enough to let individual lithium ions pass, but small enough to block anything larger.
“The special feature of this material is we can make it very thin, so we can get more energy into the same battery cell size, or we can shrink the cell size,” says Dan VanderLey, an engineer who helped found Elegus through U-M’s Master of Entrepreneurship program. “We’ve seen a lot of interest from people looking to make thinner products.”
The team is currently looking for ways to improve the flow of loose lithium ions so that batteries can charge and release their energy more quickly, Kotov says.