Misaligned Factory Robot May Have Sparked Chevy Bolt Battery Fires

An anonymous reader quotes a report from Ars Technica, written by Tim De Chant: 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. The automaker initially discovered the problem in batteries from one of LG's Korean plants, and it recalled cars with those cells last November. But then more Bolts caught fire, and other LG plants were ensnared in the investigation, spurring two expansions of the recall. The problem, GM said, has been traced to a torn anode tab and a folded separator. 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." "It wouldn't surprise me if both defects are caused by the same thing," he added. "I would imagine that the separator must be folded at the edge near where the anode tab is at. What I'm guessing is that at some point during the handling of the cell, before it's fully packaged, some part of the robot machine is catching. The tab is catching, the separator is catching -- something is catching very infrequently so that it hasn't been noticed, and it's causing this damage."

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