When a lithium-ion battery begins to overheat, it can get caught up in a vicious cycle known as thermal runaway—causing it to explode and catch fire. Now, researchers have imaged what happens inside and out the battery to understand the process.

A team from University College London used high energy synchrotron X-rays and thermal imaging to analyze batteries while they underwent extreme heating. They found that a battery with internal shielding remained largely intact until thermal runaway occurred, at which point its internal copper structure began to melt—indicating temperatures had reach around 1000 degrees C. When the team tested a battery without any internal shielding, the core quickly collapsed just before thermal runaway. Then the cell exploded, its seams bursting and contents being ejected.

That’s generally a bad thing—especially for anything in the immediate vicinity. The results are published in Nature Communications. Dr Paul Shearing, one of the researchers, explained to Phys.Org:

“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. Hopefully from using our method, the design of safety features of batteries can be evaluated and improved.”

The next step for the team is to develop their techniques in attempt to get a closer look at what happens to the cell during thermal runaway. [Nature Communications via PhysOrg]