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How a liquid that acts like a solid could prevent plane fires

Recent car crashes and airline fires have made it abundantly clear: Lithium-ion batteries, which power most portable devices and electric vehicles, are dangerous. If crushed and twisted, the porous plastic membrane that separates the electrodes inside can instantly shred and cause a short circuit, igniting the battery’s highly flammable lithium electrolyte.

Now, taking a page from children's author Dr. Seuss, chemist Gabriel Veith and colleagues at Oak Ridge National Laboratory in Tennessee may have found a solution: oobleck. The liquid mixture of cornstarch and water (which gets its name from a classic American children's book) acts like a solid if hit with sufficient force. While mixing up some oobleck for his children, Veith got an idea worthy of a cat in a hat with a vat: Replace the cornstarch with silica and mix it into the electrolyte of a lithium-ion battery to produce a variation that transforms from flammable fluid to inert solid when impacted. In chemical terms, it’s called a shear thickening fluid.

The trick was finding the right kind of silica. Other labs had tried irregularly shaped and rod-shaped silica particles, but, as they described earlier this year in Applied Materials & Interfaces, Veith’s team turned to a decades-old technique called the Stöber process to produce perfectly round nanoparticles of silica—often used to deliver medicine inside human cells. Such round particles are able to organize themselves into stronger barriers—and they’re easier to produce, Veith says. “You don’t have to reinvent the battery processing line because it’s compatible with present manufacturing technology.”

But the new goo couldn’t be injected into a battery like a normal liquid electrolyte, because the mere act of squirting turned it solid. Veith’s team found a workaround by prepositioning the silica particles within the plastic separation membrane and then injecting the liquid electrolyte afterward. Not only did his “oobleck” turn solid when impacted, it was also easier to manufacture and stronger than previously tested varieties.

Like all shear-thickening fluids, though, the Oak Ridge oobleck—patented under the name Safe Impact Resistant Electrolyte—turns back into a liquid a few seconds after impact and can still allow a fiery reaction between electrodes. Veith’s team is working on a version that turns into a brick and stays that way. He notes it could be used in military jackets that transform from wearable batteries to life-saving armor when struck by bullets. After regulatory review, the Oak Ridge team expects its technology will be implemented in batteries within a few years, starting with the least “risk averse” applications. Thing One and Thing Two would be proud.