Lithium-ion batteries are extremely popular because they are lightweight and pack a lot of power.
But when they overheat, they can catch fire. This has been a problem in airplanes, cars and now the popular gift item, "hoverboards." The Consumer Product Safety Commission says it's investigating 37 reports of fires associated with hoverboards.
Stanford University chemical engineer Zhenan Bao says she and her colleagues think they have "a very simple solution" that can prevent the catastrophic failure of batteries.
To understand how Bao's solution works, you have to understand a bit about batteries.
Batteries are essentially a sandwich: two electrodes with a substance called an electrolyte sandwiched between them. A chemical reaction inside the battery causes electrons to collect at one electrode. When you attach an electrical device to the battery, the electrons produce a current that powers the device.
Bao developed a plastic sheet that can be placed between an electrode and the electrolyte like a slice of cheese on a sandwich.
"Looks just like a normal plastic bag, but it's black in color," Bao says.
There are carbon-coated nanoparticles of nickel embedded in Bao's plastic sheet that allow the plastic to conduct electricity.
Under normal circumstances, the plastic sheet won't affect the battery's operation.
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 are pulled apart so they can no longer conduct electricity.
If the battery starts to overheat, "the plastic will sense the temperature rise and basically stops the battery from operating," Bao says. Once the battery shuts off, 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 film she and her colleagues developed reacts more quickly than other plastics.
Another feature of her plastic sheet is that when it cools down, the battery that shuts off can conduct electricity and start operating again. Of course, a battery with a tendency to overheat is probably a battery that you want to recycle.
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