Last week GM announced that it recalled more than 73,000 Chevy Bolt EVs due to battery fire risks. The automaker took action after reports of several fire incidents with Bolt EVs.
After the initial investigation, it turns out the real issue was with the car’s battery cells. Therefore, GM blamed the battery supplier LG Chem for making faulty batteries.
GM said the fires are being caused due to a torn anode tab and a folded separator. However, nothing more than this was revealed at the time. The automaker has not explained why or how the torn anode tab and folded separator are causing the fire.
Now, with the help of Mr. Greg Less, the technical director of the University of Michigan’s Battery Lab, Ars Technical has tried to explain the cause behind the fire.
What Caused Chevy Bolt Battery Fires?
According to Mr. Less, Bolt’s battery packs are made up of pouch cell types that contain layers of cathode, anode, and separator, floating in liquid electrolytes. All of this setup is encased in a flexible polymer pouch.
Greg said the torn anode would create a projection that brings it closer to the cathode, which is okay if the separator is where it’s supposed to be. Separators prevent anode and cathode from touching each other.
However, in Bolt’s battery case, the separator is not where it should be. There are two problems here that are jointly leading to fires. Greg said a torn anode alone would not have caused it because the separator would prevent it from touching.
However, the separator here is folded, which removes the gap due to which there is a high chance that Anode and Cathode bridge the gap and come in contact. If it happens, then this would cause a short; less said, “you have a short, and it’s all downhill from there.”
Furthermore, Mr. Greg Less commented, “I would imagine that the separator must be folded at the edge near where the anode tab is at. I’m guessing that some part of the robot machine is catching up at some point during the handling of the cell before it’s fully packaged. The tab is catching, and the separator is catching—something is catching very infrequently so that it hasn’t been noticed, and it’s causing this damage.”
Since this kind of defect happens infrequently, it’s tough for the Quality Control team to trace it during testing. Therefore it was tough for GM or LG to ever know about this flaw. Recalling their electric cars was the only option.
However, Greg praised GM and LG for finding out the defect in batteries early. He said it’s because it’s challenging to point out such defects.
It seems GM is facing quite a lot of problems at an early stage. It might be better because both GM and LG will learn a lot from it. It’ll eventually help them make better products.