What happens when lithium-ion batteries overheat and explode has been tracked inside and out for the first time by a UCL-led team using sophisticated 3D imaging. Understanding how Li-ion batteries fail and potentially cause a dangerous chain reaction of events is important for improving their design to make them safer to use and transport, say the scientists behind the study.

 

Hundreds of millions of these rechargeable batteries are manufactured and transported each year as they are integral to modern living, powering mobile phones, laptops, cars and planes. Although battery failure is rare, earlier this year, three airlines announced they will no longer carry bulk shipments of lithium-ion batteries in their cargo¹ planes after the US Federal Aviation Administration tests found overheating batteries could cause major fires.

 

The study by UCL, ESRF The European Synchrotron, Imperial College London and the National Physical Laboratory, published in Nature Communications today, shows for the first time how internal structural² damage to batteries evolves in real-time, and provides an indication of how this can spread to neighbouring batteries.

 

First author, UCL PhD student Donal Finegan (UCL Chemical Engineering), said: "We combined high energy synchrotron X-rays and thermal³ imaging to map changes to the internal structure and external temperature of two types of Li-ion batteries as we exposed them to extreme levels of heat. We needed exceptionally high speed imaging to capture 'thermal runaway⁴' -- where the battery overheats and can ignite. This was achieved at the ESRF beamline ID15A where 3D images can be captured in fractions of a second thanks to the very high photon flux⁵ and high speed imaging detector⁶."

 

Previously⁷, X-ray computed⁸ tomography (CT) had only been used to analyse battery failure mechanisms⁹ post-mortem with static images and to monitor changes to batteries under normal operating conditions.

 

The team looked at the effects of gas pockets forming, venting¹⁰ and increasing temperatures on the layers inside two distinct commercial Li-ion batteries as they exposed the battery shells to temperatures in excess of 250 degrees C.

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