As recently explained in Nature Energy, adding polymers and fireproofing to a lithium-ion battery’s current collectors makes it lighter, safer and about 20 percent more efficient.
Scientists at Stanford University and the U.S. Department of Energy have re-engineered one of the sheets of copper or aluminum foil known as current collectors, so they weigh 80 percent less and immediately quench any fires that flare-up. This technology could address two major goals of battery research: extending the driving range of electric vehicles and reducing the danger that laptops, cell phones, and other devices will burst into flames. The latter is especially important when batteries are charged super-fast, creating battery damage that can lead to fires.
The current collector has always been considered dead weight, and until now it hasn’t been successfully exploited to increase battery performance. But in this study, making the collector 80 percent lighter increased the energy density of lithium-ion batteries by 16 to 26 percent. That’s a big jump compared to the average increase of 3 percent in energy density achieved in recent years.
Researchers in the battery industry has been trying to reduce the weight of current collectors by making them thinner or more porous, but these attempts have had unwanted side effects, such as making batteries more fragile, more chemically unstable, or requiring more electrolytes, which raises the cost.
As far as the safety issue goes, “People have also tried adding fire retardant to the battery electrolyte, which is the flammable part, but you can only add so much before it becomes viscous and no longer conducts ions well.”
The design is based on a lightweight polymer called polyimide, which resists fire and stands up to the high temperatures created by fast battery charging. A fire retardant called TPP was embedded in the polymer, which was then coated on both surfaces with an ultrathin layer of copper. The copper not only does its usual job of distributing current, but it also protects the polymer and its fire retardant.
One of the big advantages of this approach is that the new collector should be easy to manufacture and be cheaper because it replaces some of the copper with an inexpensive polymer. Furthermore, scaling it up for commercial production should be very doable. The researchers have applied for a patent through Stanford, and they are contacting battery manufacturers to explore the possibilities.