Video UK boffins have taken a close-up of what happens with Li-ion batteries when they get hot under the collar, and it's
However, the University College London boffins say most analysis of battery fires has focussed on working what happened after the fact, using X-ray CT scans to take static images and compare those to batteries operating normally.
It's surely much more fun to use a big science machine – in this case the European Synchrotron – to capture real-time images, and that's what the UCL team, the National Physical Laboratory and Imperial College London have done.
Their images capture the process of thermal runaway as-it-happens, the UCL release says.
The study combined high-energy synchrotron X-ray images and thermal images, explains doctoral student Donal Finegan of UCL Chemical Engineering, “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”.
The quarry was the moment of thermal runaway, the moment when the battery goes from being “a bit warm” to “oh hell, my pants are on fire!”
Or, to be more scientific: when the batteries break down exothermically, they generate a lot of heat. Since that heat can't escape, the battery suffers a catastrophic failure.
What the boffins spotted included pockets of gas forming and venting inside the battery. They also found that with the right internal support, a battery can remain relatively intact in the runaway process – up until around 1,000°C when the copper melted.
“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”, the university says.
The work has been published in Nature Communications (in full here).
As Finegan explains in the video below, “we tried to simulate a range of abuse conditions, from moderate temperatures up to trying to simulate a fire”. And who wouldn't love to have the chance to try and reproduce that experiment? ®