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Why Are Those Chevy Bolt Batteries Catching Fire? Here’s One Theory

An expert explains what may have caused those Chevy Bolt battery fires.

When the batteries used in the Chevy Bolt first started catching fire, General Motors and its battery supplier, LG Chem, first attributed the problem to a defect in the way the pouch cells used in the Bolt were manufactured at one factory in Korea. But now the problem has been found to involve battery cells manufactured at other facilities. Furthermore, the software fix GM thought it had created didn’t solve the problem.

Chevrolet has recalled every Bolt ever made, including 2022 models. It is also placing the blame for the problem squarely on the shoulders of  LG Chem, which is now called LG Energy Solution. The issue does not impact the Ultium battery cells that will power GM’s upcoming EV offerings, including the Cadillac Lyriq and Hummer. Those batteries will be made at two factories jointly owned by GM and LGES.

While that partnership is solid, GM has notified LGES that it expects to be reimbursed the $1 billion it says the Bolt battery recall will cost. LG is in line to receive $2 billion in compensation from SK Innovation as a result of a trade dispute between the two companies that was resolved earlier this year. Maybe SKI should just forward the checks to GM until the LGES obligation to GM is satisfied?

GM has offered few details about its investigation into the battery fires, but has issued a terse statement that talks about a torn anode tab and a folded separator. ArsTechnica wanted to understand more about those issues so it contacted Greg Less, technical director of the University of Michigan Battery Lab. Less calls the situation a “perfect storm” that brings together several unrelated issues in a way that creates a problem no one could have foreseen.

The Bolt’s battery packs are made up of pouch 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 says, 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 says.

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 says, “you have a short, and it’s all downhill from there.”

We aren’t engineers here at CleanTechnica, (although many of our readers are), but we have been following the electric car field since the first Teslas hit the road a decade ago and know that one of the issues in battery fires to date involves dendrites — sharp protrusions that form inside conventional battery cells and pierce the separator, leading to a short circuit. Short circuits lead to overheating which can cause the electrolyte to ignite. Once one cell ignites, adjacent cells overheat and the process self-propagates until all the cells in a battery pack are involved.

The torn anode tab and folded separator are not the same as the dendrite problem, but the results are identical. “It wouldn’t surprise me if both defects are caused by the same thing,” Less says. “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.”

Keep in mind that battery cell production is not a slow, deliberative process. Elon Musk has referred to battery cells coming of the assembly line at the Gigafactory in Nevada as being like bullets firing from a machine gun. There is no time to examine each one for defects. Quality control measures randomly sample a few cells, but it’s possible for defects to pass unnoticed down the production line.

“It can’t be happening on every cell, or QC would have caught it,” Less says. “QC is usually pretty slow. You can’t look at every cell and keep the process cost-effective, I wouldn’t imagine.” One way to inspect for proper alignment of a battery’s layers is to X-ray each cell. Another is to manually tear the battery apart. Obviously that latter process is a non-starter in a production environment in which speed is a priority.

If the manufacturing defect in the Bolt batteries occurred infrequently, it’s unlikely that GM or LG could ever know the true extent of the problem without examining every pack. Recalling every Bolt may have been the only option available.

“It’s not one of these mystery cell failures, where you’re like, ‘We don’t know — something bad happened,’” Less says. “Sometimes the cell exploded, and there’s nothing left for me to take a look to figure out why.” In GM’s case, “it sounds to me like they were able to tear down some packs and find this defect with enough frequency that they’re like, ‘This is a real problem, and we need to do a recall,’ Less explains.

On the face of it, GM and LGES are facing a embarrassing situation that could stain their reputations, although Less says both are doing the right thing by stepping up and taking ownership of the problem. GM has not always been proactive about addressing safety issues, such as faulty ignition switches that could fail and lock the steering column while driving. The other issue is that here at the beginning of the EV revolution, the enemies of electric cars are hungry for any tidbit they can find that will raise fear, uncertainty, and doubt among prospective electric car purchasers, thus slowing the transition away from gasoline- and diesel-powered vehicles.

GM has not said definitely what it intends to do to fix the battery fire issue, and if you own a Chevy Bolt, you are in limbo until this gets sorted out. Your loan and lease payments still have to be made each month even though the resale and trade-in value of your car has been diminished. You are in a similar position to drivers who owned a diesel-powered Volkswagen when the emissions cheating scandal broke in 2015. When we know more, we will share it with you.

This will all get sorted out, eventually. But until it does, Chevy Bolt owners are going to be severely disadvantaged and angry, not that anyone can blame them. GM and LGES have a steep hill to climb to make this right.

 
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Written By

Steve writes about the interface between technology and sustainability from his homes in Florida and Connecticut or anywhere else the Singularity may lead him. You can follow him on Twitter but not on any social media platforms run by evil overlords like Facebook.

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