The study, published in Nature Communications today, was carried out by UCL, ESRF (European Synchrotron Radiation Facility), Imperial College London and the National Physical Laboratory, and shows for the first time how internal structural damage to batteries evolves in real-time, and how this can spread to neighbouring batteries.
The group used a combination of 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 they were exposed them to extreme levels of heat.
The high-speed imaging made possible by the European Synchrotron, which can capture 3D images in fractions of a second, and enabled the team to capture ‘thermal runaway’: the point at which the battery overheats and can ignite.
The team looked 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 degrees C.
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 ~1000 degrees C. 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.
Corresponding author, Dr Paul Shearing (UCL Chemical Engineering), said: “Although we only studied two commercial batteries,
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. This was crucial for us to better understand how battery failure initiates and spreads.
“Our results show how useful our method is in tracking battery damage in 3D and in real-time,” said UCL’s Dr Paul Shearing, one of the study’s authors. “Hopefully from using our method, the design of safety features of batteries can be evaluated and improved.”
Hundreds of millions of these rechargeable batteries are manufactured and transported each year and although battery failure is rare, earlier this year, three airlines announced they will no longer carry bulk shipments of lithium-ion batteries in cargo aircraft after US Federal Aviation Administration tests found overheating batteries could cause major fires
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