Scientists at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have reengineered one of the heaviest battery components—sheets of copper or aluminum foil known as current collectors—so they weigh 80% less and immediately quench any fires that flare up.
“The current collector has always been considered dead weight, and until now it hasn’t been successfully exploited to increase battery performance,” said Yi Cui, a professor at SLAC and Stanford and investigator with the Stanford Institute for Materials and Energy Sciences (SIMES) who led the research.
“But in our study, making the collector 80% lighter increased the energy density of lithium-ion batteries— how much energy they can store in a given weight— by 16-26%. That’s a big jump compared to the average 3% increase achieved in recent years.”
The two current collectors account for 15-50% of the weight of lithium batteries. Reducing battery weight and flammability could have a big impact on recycling, which is currently hampered by expensive, class-9 shipping restrictions.
The new current collectors are based on a lightweight polymer called polyimide, which is fire resistant and withstands the high temperatures created by fast battery charging. A fire retardant— triphenyl phosphate, or TPP— was embedded in the polymer, which was then coated on both surfaces with an ultrathin layer of copper. The copper would not only do its usual job of distributing current, but also protect the polymer and fire retardant.
Yusheng Ye, a postdoctoral researcher in Cui’s lab, said that when pouch batteries made with today’s commercial current collectors were exposed to an open flame from a lighter, they caught fire and burned vigorously until the entire electrolyte burned away. But in batteries with the new flame-retardant collectors, the fire never really got going, producing very weak flames that went out within a few seconds, and did not flare up again even when the scientists tried to relight it.
One of the big advantages of this approach is that the new collector should be easy to manufacture and also cheaper, because it replaces some of the copper with an inexpensive polymer. So scaling it up for commercial production, Cui said, “should be very doable.” The researchers have applied for a patent through Stanford, and Cui said they would be contacting battery manufacturers to explore the possibilities.