Lithium-ion batteries are integral part of today‘s world. They power our mobile phones, laptops, cars and even planes. However, even though it is quite rare for them to fail and cause damage, sometimes they burst into flames. On very rare occasions explosion can even injure people, who are, for example, talking on the phones or holding laptop on their lap. Now scientists from University College London for the first time ever were able to track exploding Lithium-ion batteries in real-time using sophisticated 3D imaging technology.
Understanding and preventing explosions of lithium-ion batteries is very important, because hundreds of millions of them are manufactured and transported each year. Despite overheating and fire being relatively rare, three airlines already announced that they will not carry bulk shipments of lithium-ion batteries in their cargo planes, because of the potential danger. New study shines a new light on the issue and shows how internal structural damage evolves in real-time how this can spread to neighbouring batteries.
Previously, X-ray computed tomography has only been used to analyse battery failing mechanisms after the failure already happened. It only provided static images and could also be used to monitor changes to batteries under normal operating conditions. Now scientists combined high energy synchrotron X-rays and thermal imaging to monitor changes to the internal structure and external temperature. They studied two types of Li-ion batteries, exposing them to extremely high temperatures. They also used high speed imaging to capture the moment then the battery overheats and can ignite.
The researchers observed the effects of gas pockets forming, venting and increasing temperatures on the layers inside two distinct commercial Li-ion batteries. They were exposed to the heat as excessing 250 degrees Celsius. The battery with an internal support remained largely intact, until the initiation of thermal runaway. Then the copper material inside the cell melted indicating temperatures up to approximately 1000 degrees C. The heat spread from inside to the outside of the battery causing thermal runaway.
The battery without an internal support structure did much worse. It exploded causing the entire cap of the battery to detach and its contents to eject. Even before the thermal runaway the core of the battery collapsed, which increases risk of severe internal short circuits and damage to neighbouring objects. Or, in worse cases, people can be injured, who are using devices with such faulty Li-ion batteries.
Despite the explosions and failures of these batteries, scientists want to stress that this was done in order to monitor internal processes of the failure of the Li-ion batteries. It is unlikely to happen in normal conditions. One of the authors of the study, Dr Paul Shearing, said that they “pushed the batteries a long way to make them fail by exposing them to conditions well outside the recommended safe operating window”. Therefore, it should not discourage people of using these batteries.
Now scientists want to study what happens with a larger sample size of batteries and in particular, they will investigate what changes at a microscopic level cause widespread battery failure. These researches should not only help to understand internal processes of batteries failing better, but can also help to find ways to improve safety. Lithium-ion batteries are very important nowadays and we should expect them to be as safe as possible.