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Batteries that put out their own fires

February 2017

How do you stop a phone from bursting into flames? Put a tiny fire extinguisher in the battery.

Although the energy densities of batteries continue to increase, safety problems (for example, fires and explosions) associated with the use of highly flammable liquid organic electrolytes remain a big issue, significantly hindering further practical applications of the next generation of high-energy batteries.

Lithium-ion batteries are used in portable devices because they are lightweight and efficient, but when they short circuit, their liquid components can vaporise and catch fire.

One way to prevent this is to add a fire-retardant chemical to the battery’s electrolyte liquid – but this hinders its performance.

To get around this, Yi Cui at Stanford University in California and his team have enclosed the fire-retardant in a thin polymer capsule. It is only released into the electrolyte if the battery overheats and the polymer shell melts. When tested in burning battery liquid, the capsules extinguished the blaze in less than half a second.

The team have fabricated a novel “smart” nonwoven electrospun separator with thermal-triggered flame-retardant properties for lithium-ion batteries. The encapsulation of a flame retardant inside a protective polymer shell has prevented direct dissolution of the retardant agent into the electrolyte, which would otherwise have negative effects on battery performance. During thermal runaway of the lithium-ion battery, the protective polymer shell would melt, triggered by the increased temperature, and the flame retardant would be released, thus effectively suppressing the combustion of the highly flammable electrolytes.

This could make lithium batteries safer for use in electric vehicles and aircraft, says Cui.

Electrospun core-shell microfiber separator with thermal-triggered flame-retardant properties for lithium-ion batteries
Liu, Kai; Liu, Wei; Qiu, Yongcai; Kong, Biao; Sun, Yongming; Chen, Zheng; Zhuo, Denys; Lin, Dingchang, Cui, Yi

Brief summary in New Scientist, 21 January 2017, p. 19 headed “Batteries that put out their own fires”

Full article: http://dx.doi.org/10.1126/sciadv.1601978

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