Diamond highlights damage pathways in lithium-ion batteries

Researchers from University College London (UCL), the NASA-Johnson Space Center, the U.S. Department of Energy’s National Renewable Energy Laboratory, the University of Warwick and the National Physical Laboratory have used Diamond’s I12 beamline to investigate how lithium-ion batteries behave under short-circuit conditions.

“Lithium-ion batteries are ubiquitous in today’s society and are used in a range of applications from mobile phones to electric vehicles,” explains first author, Donal Finegan, who is based at UCL. “Although rare, lithium-ion batteries can and do fail, sometimes catastrophically, and these failures often complete within 1-2 seconds and involve a lot of movement and dynamics.”

To induce failure, the team inserted a device capable of generating an internal short circuit on-demand and at a pre-determined location into commercially available Li-ion batteries. The team used the device to gain insight into cell design vulnerabilities by causing cell walls to rupture or cells to burst open. Using high-speed X-ray imaging, researchers monitored what happened to the structure of the cells in real-time, as the short circuit drove the catastrophic failure process that propagated through cells and modules.

Individual cells, as well as small cell modules, were tested at Diamond and the European Synchrotron Radiation Facility (ESRF) in France under conditions that represented a worst-case battery failure scenario. Short circuits were initiated inside the batteries at ~60 ˚C. During the failure process, cell temperatures reached in excess of 1085 ˚C.

“After visiting ESRF and processing the data, we discovered that with a little more work and additional experiments we could create a much more comprehensive study,” continues Finegan. “Fortunately we were able to get the beamtime at Diamond where we could build on the earlier work we’d done at ESRF.”

“The exceptionally high-intensity X-ray flux at Diamond provides the high-speed imaging capability necessary to capture such rapid events in real time,” adds Michael Drakopoulos, Principal Beamline Scientist on the I12: Joint Engineering, Environmental, and Processing (JEEP) beamline. “This allows our users to study, in detail, the fastest failure mechanisms of commercial cell designs, and use the results to guide design-improvements for higher performance and safe lithium ion batteries.”

From analysing the high-speed imaging frame by frame, the team looked at the effects of gas pockets forming, venting and increasing temperatures on the layers inside two distinct commercial Li-ion batteries and identified consistent failure mechanisms.

The team now plans to examine how these new insights can be used to improve the safety of commercial battery and module designs. For example, researchers will study how the rupture of the highest energy density commercial cells can be prevented and how to reduce the risk of cell-to-cell propagation.
 

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