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Flame Retardant in Lithium-ion Batteries Could Quench Fires

Additive could extinguish flames in less than half a second

2 min read
Liu et al./Science Advances
Liu et al./Science Advances

A powerful flame retardant added to lithium-ion batteries that only gets released when the devices get too hot could help keep them from catching on fire, a new study finds.

When lithium-ion batteries overheat, they can burn through clothing, burst into flames and even explode. Such "thermal runaways" have led some engineers to explore the creation of lithium-ion batteries with their own fire alarms or chemical additives that can prevent short circuits.

Researchers previously tried adding flame retardants directly into the batteries’ electrolytes, which connect the electrodes of the energy storage devices. However, these approaches significantly reduced battery performance.

Now researchers have designed a lithium-ion battery in which the separator, the component that keeps the battery's positive and negative electrodes apart, contains a cheap, powerful, and commonly used flame retardant known as triphenyl phosphate.

During normal battery operation, the flame retardant stays encapsulated within plastic fibers. If the separator gets hotter than 150 degrees C, the plastic melts, releasing the flame retardant. In experiments, the chemical completely quenched flaming electrolyte in 0.4 seconds. The scientists detailed their findings online in the 13 January edition of the journal Science Advances.

How flame retardant can stop lithium-ion battery fire.Illustration: Liu et al./Science

“Using our ‘smart’ separators, battery electrochemical performance will not be affected by the flame retardant under normal conditions," says study senior author Yi Cui, a materials scientist at Stanford University in California. “However, once there is a potential thermal runaway, the flame retardant will be activated and nip the fire or explosion in the bud.”

Future research can explore how well this separator responds to electrical abuse such as overcharging or discharging too deeply, or physical abuse such as crushing or penetration, Cui says. “We believe our safe separator should find broad applications, considering that more and more fires and explosions of lithium-ion batteries have been reported recently.”

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The Transistor at 75

The past, present, and future of the modern world’s most important invention

2 min read
A photo of a birthday cake with 75 written on it.
Lisa Sheehan

Seventy-five years is a long time. It’s so long that most of us don’t remember a time before the transistor, and long enough for many engineers to have devoted entire careers to its use and development. In honor of this most important of technological achievements, this issue’s package of articles explores the transistor’s historical journey and potential future.

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