GM Confirms Cause of Bolt Battery Fires, Rolls out New Monitoring Software

The software will initially limit Bolt customers to charge their cars to 80% SOC. As confidence in the software increases, GM will raise the SOC limit.

September 21, 2021

Lindsay Brooke

A folded cell separator and torn anode occurring simultaneously in the same battery cell has been confirmed as the root cause of 13 recorded Chevrolet Bolt EV battery fires. (Chevrolet)

One of GM’s top battery experts has confirmed that the root cause of 13 Chevrolet Bolt EV battery fires, which caused GM to recall every Bolt sold since 2017, is related to a cell-manufacturing issue rather than cell architecture or design, as the company had previously estimated.

“We’re very confident that this is a manufacturing defect that occurs during the assembly of the cell and the pack,” asserted Tim Grewe, GM’s general director of electrification strategy and cell engineering, during a media call on Sept. 20. “We have numerous customers with 300,000-400,000 miles on their vehicles [proving that] when these cells are properly manufactured they are durable, have very long life and are very stable.

Grewe said the manufacturing defect found within battery supplier LG Energy Solution’s manufacturing processes at its highly-automated Holland, Michigan, battery plant and Hazel Park, Michigan, pack assembly facility, has caused battery-cell anodes to tear and cause cell separators to fold in the relatively few Bolt vehicles that have caught fire, out of about 141,000 vehicles total. GM and LG investigations concluded that both defects must be present in the same cell to create the rare condition for a cell to potentially overheat and catch fire, he noted.

Teams of GM and LG manufacturing engineers have updated and implemented new manufacturing processes at the LG facilities, and LG is working with GM to ramp-up other battery-production facilities around the globe. As a result of their confidence in the root cause of the issue and in a new battery-monitoring software to be installed in customer vehicles, LG has resumed battery cell, module and pack production at both of its Michigan plants. Bolt production at GM’s Orion Township (Michigan) will remain suspended until mid-October. This will allow the automaker to provide Bolt owners with replacement battery modules during the same time period.

Re-starting battery production will allow GM to provide Bolt owners with replacement battery modules as soon as mid-October, the company stated. GM will continue to prioritize Bolt owners for replacement modules based on two factors: the specific build window of customer vehicles and customer charging behavior. The charging behavior GM is specifically trying to address is ‘deep discharge’ – running the battery down to nearly zero state-of-charge (SOC) then fully or near-fully recharging. Those two factors add to the possibility of a fire risk.

Within the next 60 days, GM engineers will deploy into the Bolt customer base a new diagnostic software that will continue to monitor battery performance and alert the customer of any battery anomalies. The software will initially limit Bolt customers to charge their cars to 80% SOC. As the software increases GM’s confidence of battery performance, GM will raise the SOC limit, Grewe explained. When the new software is installed, customers also will be able to resume charging their vehicles overnight unattended and parking their vehicles in their garage, the company said.