Dangerous, overheating batteries to become a thing of the past

11 January 2016
By Jack Loughran
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Previous technology used to prevent batteries from overheating has left them unusable unlike the new polymer

Previous technology used to prevent batteries from overheating has left them unusable unlike the new polymer

A lithium-ion battery that automatically shuts down before it overheats has been developed by Stanford University researchers.

Lithium-ion batteries are typically used in modern smartphones and tablets, as well as larger devices such as laptops and electric cars.

On rare occasions, batches of malfunctioning batteries have been known to catch fire inside user’s bags or pockets which represents a significant health hazard.

In 2013, shares in Tesla Motors plummeted after one of its Model S vehicles burst into flames due to an issue with its battery.

The researchers have developed a polymer to overcome this problem which stops conducting electricity at high temperatures and immediately resumes once heat has dissipated.

“With the ever-increasing capacity of current batteries, the risk of them catching fire has become higher and higher,” said Stanford professor Zhenan Bao.

"People have tried different strategies to solve the problem of accidental fires in lithium-ion batteries."

"We've designed the first battery that can be shut down and revived over repeated heating and cooling cycles without compromising performance."

Several techniques have been used to prevent battery fires in the past, such as adding flame retardants to the electrolyte.

The problem with these solutions is that once they are used, the battery becomes useless and needs to be replaced unlike this new solution, which allows it to continue to function normally once it has cooled down.

The polymer used contains ‘spiky particles’ that conduct electricity when touching but separate when heated, preventing current from flowing.

When the researchers heated the battery with the polymer above 70°C, the material quickly expanded and it shut down. Yet when the temperature dropped back down to normal operating levels the polymer shrank, bringing the particles back into contact and the battery started generating electricity again.

"We can even tune the temperature higher or lower depending on how many particles we put in or what type of polymer materials we choose," said Bao. "For example, we might want the battery to shut down at 50°C or 100°C."

"Compared with previous approaches, our design provides a reliable, fast, reversible strategy that can achieve both high battery performance and improved safety," said Stanford engineer Yi Cui who has also been working on the project. "This strategy holds great promise for practical battery applications."

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