Overheated lithium batteries can be detected by X-ray.

Overheated lithium batteries can be detected by X-ray.

Overheated lithium batteries can be detected by X-ray.

Overheated lithium-ion batteries can be x-rayed to reveal safer batteries.

The so-called thermal runaway phenomenon is that when the lithium-ion battery is overheated, the package will burn through, suddenly burn, or even explode. Although the odds are slim, engineers have ample opportunity to explore how to prevent possible fires.

Scientists at University College London have used a synchrotron radiation facility to scan overheated lithium-ion batteries for the first time, hoping to improve their planning and safety. Particle accelerators produce X-ray images with higher resolution than conventional X-ray machines. Their findings were published in the April 28 issue of the journal Nature Communications.

The scientists first heated two fully charged commercial lithium-ion batteries (above 250 degrees Celsius) with a hot air gun, then imaged them with X-rays at a 1250 frame rate, and then combined thermal imaging to study them. They finally investigated the rapid destruction of the internal structure of lithium-ion batteries before the thermal runaway.

They found that both batteries had thermal and electrochemical reactions and that air bubbles formed inside the batteries could cause the batteries to deform. Inside the battery, highly conductive parts come into contact with each other, causing a short circuit. After that, the pressure inside the battery rises rapidly, and when the lid is opened, oxygen enters, further exacerbating the loss of heat. It may be that the battery is covered, the enclosed space is favorable for a thermal response, and the hot and molten material is ejected from the battery holes. In the second case, the internal temperature can even exceed 1085 degrees Celsius with molten copper.

Under extreme conditions, high charge-discharge rates, overcharge, and undercharge can lead to catastrophic failure of lithium-ion batteries. The researchers believe this could be verified in future analyses. They also advocate for puncture and smash testing to help develop safer battery programs.

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