Battery “kill-switch” prevents overheating and fires

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Polyethylene film embedded with nanoparticles shuts off current flow before batteries overheat

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Researches at Stanford University have developed a lithium-ion battery that automatically shuts off before it overheats, and restarts instantly once it cools down. The simple add-on to existing battery technology could help prevent battery fires in laptops and other electronic devices.

The technology functions like a kill switch, or a trip switch in a fuse box that resets on its own.

For some time researchers have been seeking solutions to the accidental fire problem associated with lithium-ion batteries, including adding flame retardants to the battery's electrolytes, all without success. The Stanford battery is the first designed to stop and start over repeated cycles of heating and cooling without diminishing performance.

The researchers started with spiky nickel nanoparticles and coated them with graphene. The particles were then embedded in a film of elastic polyethylene, which were attached to one of the battery electrodes. As long as the nanoparticles in the film are in physical contact with each other, the current can continue to flow without interruption.

When the battery heats up to 160ºF (70ºC), the polyethylene film stretches and expands like the skin of a balloon. This causes the particles to physically separate and thus stops the current from flowing, shutting down the battery. Then as soon as the temperature of the battery drops back below 160ºF, the film shrinks and the particles come back into contact with each other, allowing the current to once again start flowing.

The temperature threshold can be raised or lowered as needed by changing the number of nanoparticles on the film, or choosing a different type of polymer material.

The researchers say the approach would be easy to incorporate current battery production. "We can use exactly the same battery production line," says Zheng Chen a researcher on the project, and a post-doctoral chemical engineer at Stanford. "The addition of the film can be completed during the production of metal current collectors, which is an intrinsic separate process."

Chen adds the cost of the process would be low. "The major part of the thin film is polyethylene, which is one of the cheapest polymers," she says. "And nickel conductive particles are also commercially available at large scale. We do not have exact numbers, but are sure the cost addition will be very small.

Professor Zhenan Bao explains the new battery in the video below. The research was published this month in Nature Energy.

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