National Physical Laboratory

Tracking exploding lithium-ion batteries in real-time

Researchers at the National Physical Laboratory (NPL), UCL, the European Synchrotron Radiation Facility (ESRF) and Imperial College London have shown for the first time how heat-induced damage to lithium-ion (Li-ion) batteries evolves in real-time and leads to failure.

Battery showing thermal runaway during thermal abuse tests (Credit: Donal Finegan, UCL)
Battery showing thermal runaway during thermal
abuse tests (Credit: Donal Finegan, NPL/UCL)

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 Li-ion batteries in their cargo planes after US Federal Aviation Administration tests found that overheating batteries could cause major fires.

The thermal response of a battery is one of the most important characteristics to understand when assessing the safety of its design. Undesirable increases in temperature can occur within a battery due to the presence of an external heat source, such as the failure of a neighbouring battery. Depending on the design, critical temperatures exist above which heat generation exceeds dissipation, triggering 'thermal runaway' which can lead to ignition. 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.

The UCL-led study, published in the journal Nature Communications, used high-speed synchrotron X-ray computed tomography and radiography, together with thermal imaging, to track changes to the internal structure and external temperature of Li-ion batteries as they were exposed to extreme levels of heat.

The researchers used the high-frequency imaging capability provided by the beamline at ESRF to track for the first time the rapid internal structural deformation leading up to and during thermal runaway. This new approach allowed the team to look at the effects of gas pockets forming, venting 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 ºC.

The battery with an internal support remained largely intact up until the initiation of thermal runaway, at which point the copper material inside the cell melted indicating temperatures up to around 1000 ºC. This heat spread from the inside to the outside of the battery causing thermal runaway. In contrast, the battery without an internal support exploded causing the entire cap of the battery to detach and its contents to eject. Prior to thermal runaway, the tightly packed core collapsed, increasing the risk of severe internal short circuits and damage to neighbouring objects.

These results enhance our understanding of the most dangerous failure mechanism of such devices and highlight the impact of engineering design on the performance and safety of commercial Li-ion batteries. Use of the techniques developed could lead to major improvements in the design of Li-ion batteries and their safety features. The team now plan to study a larger sample size of batteries and the changes at a microscopic level which cause widespread battery failure.

Lead author Donal Finegan received the inaugural Sheelagh Campbell Award from the Royal Society of Chemistry in recognition of this work. The award was established to recognise excellence in postgraduate research in the field of electrochemistry. Donal's CASE studentship is jointly funded by NPL and UCL on in situ diagnostics for lithium ion batteries.

This work was carried out as part of a strategic partnership between UCL, Imperial and NPL in the area of in-situ diagnostics for electrochemical energy conversion devices, which has seen NPL co-fund a number of PhD studentships and postdoctoral research fellows in recent years. This collaboration has clear benefits to NPL in generating complementary funding from the Engineering and Physical Sciences Research Council (EPSRC) for metrology-focused research, accessing world class research facilities and building strong networks for future opportunities.

Find out more about NPL's work on Electrochemistry

For more information, contact Gareth Hinds

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Last Updated: 26 Apr 2017
Created: 29 Apr 2015

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