- Every Chevrolet Bolt EV and Bolt EUV that GM has made is under recall because their batteries could be defective and cause a fire.
- What is it about the batteries—lithium-ion cells sourced from LG Energy Solutions and made on two different continents—that could have led to this?
- Car and Driver talked to a battery engineer who gave us the full explanation. Plus, we give Bolt owners a checklist of what to do and how to get more information from Chevrolet.
General Motors has planned a full suite of electric vehicles launching over the next five years. So the ongoing recall of Chevrolet Bolt EV batteries—for which replacements can’t even start until GM works out what went wrong—threatens to cast a pall over the fall debut of the 2022 GMC Hummer EV pickup and next spring’s launch of the 2023 Cadillac Lyriq.
The recall has become a slow-motion catastrophe since it started last November. That was when GM identified 50,930 Bolt EVs from model years 2017 through 2019 that might have defective cells. That number later grew to 68,700 vehicles. In July, it recalled the same cars again after its engineers identified two potential defects that could, in rare cases, be present in the same cell.
Then it got worse: On August 20, out of “an excess of caution,” GM added all 63,680 Bolt EV and EUV models from the 2020 model year through the present day, along with a further 9340 Bolts from the 2019 model year that hadn’t been previously recalled.
The new Bolt EUV model was just being delivered to dealers; activities around that launch are now suspended. Meanwhile, Chevrolet had lowered Bolt prices considerably for 2022, recasting the car as an affordable entry-level EV complementing the upcoming luxury GMC and Cadillac models.
The total recall now numbers 141,000 electric vehicles over six model years, every Bolt the company has built since sales began in December 2016. No schedules have been given for any cell replacements. Roughly a dozen fires in Bolt EVs have been publicly identified. To date, no injuries or deaths are attributed to the problem.
But Bolt EV owners are confused, even as many continue to use their cars while parking and charging them outside. More troubling, the recall and the prospect of Bolt fires has spread. Bolts are apparently banned from one outdoor parking lot in San Francisco, for instance, where a sign cited “public safety” as the reason.
Still, there’s little reason for public panic or widespread bans on EVs. “Yes, we’ve seen some battery fires, but the numbers are small, and they need to be put into perspective,” Sam Abuelsamid, lead auto analyst for Guidehouse Insights, told NBC News.
Not Just Korean Cells
The Bolt’s lithium-ion cells were provided by GM’s longtime battery supplier LG Energy Solutions (the battery arm of giant Korean manufacturer LG). For several months, the carmaker believed the affected cells were limited to those produced in LG’s plant in Ochang, Korea. Those cells were used only in 2017–2019 Bolt models.
Then in July, it said: “After further investigation into the manufacturing processes at LG and disassembling battery packs, GM discovered manufacturing defects in certain battery cells produced at LG manufacturing facilities beyond the Ochang, Korea, plant.” That means LG’s U.S. plant in Holland, Michigan, which supplied cells for the 2020–2022 Bolt line, was also affected.
So what went wrong?
GM says it has identified two different manufacturing defects.
Two Defects
One is a torn anode tab, the piece of the negative electrode that allows the cell to be wired into a group of cells, called a module, and then into full battery pack. The other is a folded separator, the thin sheet of material (typically a nonwoven polymer) that separates the anode and cathode.
In rare cases, GM said, the two defects may be present in the same cell, increasing the chance of a fire within affected cells, which can then spread through the module. GM told Bloomberg its modules are “passive propagation resistant,” meaning that fires in one module should not spread to adjacent modules. Nonetheless, a fire within even part of the battery pack remains a serious event, one that can damage a vehicle substantially.
Since GM has declined to comment beyond the wording in its August 20 press statement, we asked Haresh Kamath, who designed battery cells for spacecraft at Lockheed Martin, to give us his take on what GM’s statements meant. He’s presently the director of distributed energy resources and energy storage at the Electric Power Research Institute (EPRI), the R&D arm of the U.S. electric utility industry.
A main principle of all device design, Kamath said, is to avoid single points of failure. He suggests that neither of the faults named by GM by itself leads to a cell failure. “Each of these things is not a big deal” individually, he said. But, in the very rare case that they both occur within the same cell, the combination of the two can create a point of failure—but not one either LG or GM likely thought to test for.
How could the companies only have become aware of the combined faults now, after 141,000 Bolts were built and sold over five years?
Defect Rates and Specific Use Conditions
Kamath suggests two possible sets of circumstances that could have produced the combination of flaws that apparently led to short circuits in one or more cells, and subsequent fires.
First, some unrecognized defect in the manufacturing process may have caused one flaw to occur at a higher rate than projected—even though, by itself, that flaw would not have led to a short circuit. A purely hypothetical example of the resulting math would be a projected rate of one flaw occurring in every 1 million cells that was actually far higher: say once in every 10,000 cells.
Other battery experts have offered reasons for how and why the flawed cells may have been produced. One suggestion: a misaligned robot on a cell production line.
Second, some combination of specific vehicle uses may be required for the pair of faults to produce a serious short within the cell. Those may be operating conditions—does the driver use full acceleration often, drawing maximum current from the cells?—and other factors including ambient temperatures, charging rates, and whether the battery packs are routinely charged to full capacity and then depleted almost to zero percent.
Those variable use conditions combine to produce a different pattern of heating and cooling for virtually every Bolt EV pack. Perhaps, Kamath said, only some sets of repeated use conditions exacerbated the pair of manufacturing flaws—one of which may have occurred at a considerably higher rate than expected—to the point where the cell’s expansion and contraction caused a short.
Both GM and LG clearly have scores of battery engineers devoting far more than 40-hour weeks to trying to answer these questions—often a tough task in a battery pack from a burned car.
What Now?
While GM has committed to replacing affected battery modules, it says it won’t do so until it’s confident it has identified the root causes of the defects. It believes they lie in the manufacturing process, but it hasn’t ruled out design defects. Meanwhile, all Bolt production has been suspended, and new Bolt models are not available to buy.
Added together, the three recalls are expected to cost GM about $1.8 billion. The company took an $800 million charge this year, and it has said it will pursue reimbursement from LG for $1 billion in additional costs related to the expanded recall and future fixes.
The more cells and modules GM ascertains need to be replaced, the greater the concern over availability of suitable cells. Full replacement of all 141,000 battery packs would require sourcing roughly 8.4 gigawatt-hours of new cells from LG—cells that GM likely has not planned for.
While GM and LG are separately building two joint-venture cell plants to fabricate GM’s next-generation Ultium cells—to be used in more than a dozen EVs starting production late this year—those cells have a different chemistry, use a different battery-management system, and are even a different size than the Bolt cells. GM is unlikely to explore the possibility of using them in Bolts.
It is unclear whether manufacturing defects in the LG cells delivered to GM affect other cells it provided to other carmakers. Earlier this year, Hyundai recalled 82,000 of its own electric cars, which used LG Chem cells that the Korean carmaker said posed a fire risk. The cost of roughly $900 million was split between LG and Hyundai. There was also a recent recall for LG residential battery-storage systems purchased from 2017 to 2019.
This week, the Detroit News reported that the National Highway Traffic Safety Administration (NHTSA) has asked LG Energy Solutions whether any other electric cars that use its cells have been affected by the same problems.
What Should Bolt Owners Do?
In August 2021, GM advised that until replacement modules can be installed, owners of all Bolts should:
(1) Set their vehicle to a 90 percent state of charge limitation using Target Charge Level mode. GM asks customers who are unable to successfully make these changes, or do not feel comfortable doing so, to visit their dealer to have these adjustments completed;
(2) Charge their vehicle more frequently and avoid depleting their battery below approximately 70 miles of remaining range, where possible; and
(3) Park their vehicles outside immediately after charging and not leave vehicles charging indoors overnight.
Bolt EV customers can visit Chevrolet’s Bolt recall site, call the Chevrolet EV Concierge at 833–EVCHEVY, or contact their preferred Chevrolet EV dealer.
Some early research for this story was done for an earlier summary of the Bolt EV battery recall prepared by the author for the Electric Power Research Institute (EPRI).
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Source: Motor - aranddriver.com
