STEVE INSKEEP, HOST:
Spend some time around elementary-school-aged kids, and you will hear these two things. First, someone will say, I really want a hoverboard - you know, those things that are like scooters but without a handle. You just kind of hover above the ground. Second, you will hear this - I want a hoverboard as soon as they stop catching fire. The Consumer Product Safety Commission says it's been investigating dozens of reports of fires associated with hoverboards, fires likely caused by problems with lithium batteries. NPR's Joe Palca has been exploring new inventions as part of his series, Joe's Big Idea. And today, he has the story of a chemical engineer who invented a way to prevent lithium battery fires.
JOE PALCA, BYLINE: Lithium batteries are popular because they're lightweight and can store a lot of energy. They're used in everything from computers to jet aircraft. But lithium can be nasty. Get it hot enough, and it'll catch fire. Now, under normal operating conditions, lithium batteries are perfectly safe. But if they overheat, if, say, the battery is overcharged or develops a short circuit, then watch out.
ZHENAN BAO: The problem we're trying to solve is to come up with a very simple solution that can prevent the catastrophic failure of battery before such accident will happen.
PALCA: That's Zhenan Bao. She's a chemical engineer at Stanford University. Bao's simple solution involves a thin plastic sheet.
BAO: Looks just like a normal plastic bag, but it's black in color. And we insert this sheet of plastic inside the battery on top of the electrode.
PALCA: Batteries are essentially a sandwich - two electrodes with a substance called an electrolyte sandwiched in between. Bao's thin plastic sheet goes between the electrodes and they electrolyte, like a slice of cheese on a sandwich. There are carbon-coated nanoparticles of nickel embedded in Bao's plastic sheet. These allow the plastic to conduct electricity so the battery can operate normally. But the plastic has a remarkable property - it expands when it heats up. And when it expands, the carbon-coated nickel nanoparticles in the plastic sheet are pulled apart, and they can no longer conduct electricity. So if the battery starts to overheat...
BAO: ...The plastic will sense the temperature rise and basically stops the battery from operating.
PALCA: And when the battery stops operating, it cools down all by itself. Bao describes her research in the journal Nature Energy. Bao says others have tried similar approaches, but she says the plastic she and her colleagues have developed reacts more quickly than other plastics, making it that much safer. Joe Palca, NPR News.