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3D View of Melting Li-ion Batteries Helps Improve Safety

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_82618688_thermalEngineers from University College London put lithium-ion batteries to the most challenging of tests in order to find ways to improve safety.

When it comes to energy storage, lithium-ion (Li-ion) batteries are currently the leaders by miles. We all have them around us, or even on us, for the majority of the day, probably without even thinking that anything could go wrong. Mobile phones, cameras, digital watches, laptops- all powered by small Li-ion batteries.

On this small scale of things, people are more concerned about running out of charge than about safety, but when it comes to powering larger items like electric cars, airplanes, or storing energy from renewable energy power plans, the priorities drastically change.

Considering the significant number of scary accidents, when batteries powering EVs catch fire, no wonder engineers around the world are now taking the issue much more seriously. Many are trying to find ways to understand what exactly goes inside these energy storage devices that can cause deterioration, serious damage, or explosion.  But while some are looking for practical solutions, others are going way beyond the conventional means in order to test the limits of the precious Li-ion power-storage.

In the latest issue of Nature Communications, a team of engineers from University College London published the results from their detailed study on finding the reason behind failure and explosion of Li-ion batteries due to overheating. This is the first time anyone produces a 3D view of batteries exposed to extremely high temperatures. The team used both a thermal camera and a synchrotron X-ray to follow the process of arising and spreading of faults that ultimately end in an explosion.

The aim was to simulate the worst case scenario and expose the batteries to extreme conditions, which are very unlikely to occur in day-to-day life. With that, the guys were hoping to understand precisely what goes on inside the energy storage devices and hopefully gather enough knowledge that can later be applied in designing the ultimate safety features.

They used two batteries for the experiment. One of them has a cylindrical support built into its core, while the other one does not. The two batteries were exposed to a temperature of 250 degrees C within a particle accelerator, which rotates and produces X-rays. Thanks to this instrument, the team was able to observe the deterioration of the batteries from all angles and inside all layers. The X-rays showed them the gradual breakdown and melting of the inside layers, while the thermal camera gave them a live footage of the warming up leading to an explosion.

The team was able to follow closely the process of “thermal runaway”, where chain reaction is triggered due to exposure to an extremely high temperature. They found out that under the same conditions, the battery without a cylindrical support experienced thermal runaway much sooner than the one with the support (161 seconds versus 217 seconds). The team, however, was much more intrigued by the actual process of thermal runaway, as no one has ever been able to follow it from start to end so closely and in so much detail.

The guys are now looking into placing the batteries under other extreme conditions, such as electrical overload. They are convinced that their method allows much better tests that could lead to much safer energy storage in the future.

Image (c) Nature Communications

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