Lithium ion batteries are used in a wide range of applications and technologies. As it happens; if you are reading my blog on a smartphone, laptop or tablet, you are probably holding one right now. From mobile phones to electric cars, Li-ion batteries are all around us, but how do we make sure they are safe?
As I have remarked previously in my blog ‘Bulletproof batteries‘, there are significant safety issues associated with Li-ion batteries. In 2013, a problem with overheating batteries forced airlines to ground their Boeing 787 ‘Dreamliner’ aircraft, after reports of batteries bursting into flames.
The use of Li-ion batteries is becoming more wide-spread. So we need to gain a better understanding of the hazards and risks associated with their use.
That’s why a research group led by chemical engineers from University College London (UCL) UK, with the European Synchrotron (ESRF), Imperial College London and the National Physical Laboratory, have been working to figure out what happens to Li-ion batteries when they overheat and explode.
Li-ion battery design and safety performance can be improved through a better understanding of what happens when they fail.
Paul Shearing, a senior lecturer in chemical engineering at UCL and winner of the 2014 IChemE Young Chemical Engineer in Academia Award, said: “We walk around with Li-ion batteries in our pockets every single day and by and large, nothing goes wrong.”
“We’re very positive about these batteries. But we’re also conscious of the fact that as we move from iPhones and digital cameras and laptops, to things like aerospace batteries and aeronautical batteries and electric vehicles – these batteries are operating in more and more demanding conditions.”
Using sophisticated 3D imaging, the team captured in real time the chain reaction of events that resulted in damage to the batteries’ internal structure. They also investigated the mechanisms through which the damage spreads to adjacent cells.
The study was led by chemical engineering PhD student, Donal Finegan, who said: “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.
“We needed exceptionally high speed imaging to capture ‘thermal runaway’ – where the battery overheats and can ignite. This was achieved at the ESRF’s ID15A beamline where 3D images can be captured in fractions of a second thanks to the very high photon flux and high speed imaging detector.”
Paul and Donal describe their research in this YouTube clip:
The team exposed two batteries to temperatures in excess of 250°C. This enabled them to examine the effects of gas pocket formation, venting and temperature increases that resulted in a thermal runaway chain reaction.
Batteries with internal safety features fared better, remaining intact until thermal runaway occurred at temperatures up to 1000°C. However, batteries without internal support exploded before thermal runaway occurred. Some battery cores collapsed, significantly increasing the risk of severe internal short circuits.
Paul said: “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. The destruction we saw is very unlikely to happen under normal conditions because we pushed the batteries a long way to make them fail by exposing them to conditions well outside the recommended safe operating window.
“It was crucial for us to better understand how battery failure initiates and spreads. Hopefully by using our method, the design and safety features of batteries can be evaluated and improved.”
The team published their findings in the journal, Nature Communications: ‘In-operando high-speed tomography of lithium-ion batteries during thermal runaway‘.
They plan to investigate even more batteries and will also analyse battery failure at a microscopic level.
Next time you, or a loved one, boards a Boeing 787, your journey will be even safer thanks to the work of chemical engineers like Paul and Donal. I look forward to seeing how their research develops.
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