A team from the University of College London (UCL) has tracked what happens when lithium-ion batteries overheat and explode.

The team used high-energy synchrotron X-rays and thermal imaging to see what happens both inside and outside of the batteries when they are exposed to extreme heat. (view video here)

A Li-ion battery as seen using thermal imaging to map changes in internal and external structure and temperatures. Source: UCL“We needed exceptionally high speed imaging to capture 'thermal runaway'—where the battery overheats and can ignite," says study leader Donal Finegan, a UCL chemical engineering graduate. “This was achieved at the ESRF (European Synchrotron Radiation Facility) beamline ID15A where 3D images can be captured in fractions of a second—thanks to the high photon flux and high speed imaging detector”.

The study, published in Nature Communication, shows how internal structural damage to batteries happens in real-time and indicates how it can spread to neighboring batteries. The researchers say this type of work is important because they can better understand how to improve battery design and make them safer to use and transport.

The team exposed the battery shells to temperatures in excess of 250° C and looked at the effects of gas pockets forming, venting and increasing temperatures on the layers inside two commercial lithium-ion batteries.

“Although we only studied two commercial batteries, our results show how useful our method is in tracking battery damage in 3D and in real-time," says Paul Shearing, one of the researchers. “The destruction we saw is very unlikely to happen under normal conditions as we pushed the batteries a long way to make them fail by exposing them to conditions well outside the recommended safe operating window."