A 3D picture of the insides of an extremely overheated lithium ion battery

Exploding Li-ion batteries analysed to identify cause

Researchers have captured what happens inside overheating and exploding lithium ion batteries using sophisticated 3D imaging technology.

The researchers believe the data could help improve design and safety of the omnipresent technology used not only in smartphones and tablets, but also in electric cars and aeroplanes. The first study of its kind, the work was published in the Nature Communications journal. 

"We combined high-energy synchrotron X-rays and thermal 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,” said Donal Finegan, a PhD student at University College London (UCL) and lead author of the study, produced jointly by  UCL, Imperial College London, the European Synchrotron Radiation Facility (ESRF) and the UK National Physics Laboratory.

“We needed exceptionally high-speed imaging to capture 'thermal runaway', 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 flux and high-speed imaging detector," Finegan explained.

The team looked at the effects of gas pockets forming, venting and increasing temperatures on the layers inside commercially available lithium ion batteries with and without internal support as they exposed them to temperatures above 250 degrees Celsius.

The accuracy of the imaging equipment allowed the researchers to observe how the damage evolves in real time and how it can spread to neighbouring batteries.

While batteries with internal support remained largely intact up until the initiation of the thermal runaway when their copper core melted at temperatures around 1000 degrees Celsius, batteries without internal support exploded, ejecting their contents.

"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,” said Paul Shearing from UCL Chemical Engineering. “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.”

Improving the safety features of lithium ion batteries is crucial as these devices have caused concern in the past over their flammability. Multiple aerospace firms as well as aviation bodies have said transporting lithium ion batteries on passenger planes could cause safety hazards and thus should be prohibited.

Previously available data on the damage inside the batteries came only from X-ray and computer tomography inspections conducted after an incident. Alternatively, the researchers were able to monitor changes inside the batteries in regular operating conditions.

The team now plans to study what happens with a larger sample size of batteries. In particular, they will investigate what specific changes at the microscopic level can cause widespread battery failure.

 

Video from the Li-ion battery experiment:

 

 

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