Misaligned factory robot may have sparked Chevy Bolt battery fires

GM announced last Friday that it was recalling every Chevrolet Bolt it had ever made, including the new electric utility vehicle model that debuted this year. After a string of fires affected Bolt models, the company traced the problem to two simultaneously occurring defects in the cars’ LG Chem-made batteries.

That’s all GM has said so far. It hasn’t said how widespread the defects are, nor has it said how, exactly, the fires started. But in what little information has been released, and in the timing of GM’s recalls, there are clues. To decipher them, Ars spoke with Greg Less, technical director of the University of Michigan’s Battery Lab.

“What we’re looking at is a perfect storm,” Less said. The Bolt’s battery packs are made up of pouch-type cells, which are essentially layers of cathodes, anodes, and separators that are flooded with liquid electrolyte and encased in a flexible polymer pouch. The torn anode tab, he said, would create a projection in what should be an otherwise flat battery. The projection brings the anode closer to the cathode. “And that would probably be OK if the separator was where it was supposed to be,” he said.

But in problematic Bolt batteries, the separator wasn’t where it was supposed to be. Separators are placed between the anode and cathode to prevent the two electrodes from touching. A torn tab wouldn’t necessarily be an issue on its own because the separator would prevent any projection from bridging the anode-cathode gap. In cells with a folded separator, though, the gap would be missing from at least part of the battery. If the anode bridges the gap, Less said, “you have a short, and it’s all downhill from there.”

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