Last month Mitsubishi Motors Corporation (MMC) reported one instance of a fire occurring in one of the drive battery packs used for MMC's electric vehicles (EV) on March 18 at its Mizushima Plant in Okayama prefecture in Japan.
One of the 16kWh drive battery packs used in the i-MiEV (lithium-ion battery) overheated in the battery inspection room at the EV assembly factory at the Mizushima Plant. The drive battery pack started to smoke, and then ultimately caught fire one hour later. The battery pack was charging whilst connected to charge-discharge inspection equipment as part of the final inspection.
The joint investigation with the lithium-ion battery supplier revealed that the battery cell defect originated from a part of the supplier's manufacturing line, resulting in short-circuited battery cells. The defect occurred in a screening process that was added to the manufacturing line in December 2012. It was found that during this screening process the shape of an internal part of the battery cell was altered and some microscopic contaminants were generated as a result of battery cells being exposed to excessive force. The screening process where the defect was occurring has now been removed.
For more on Lithium-ion battery manufacturers read Analysis of 138 Lithium-based Rechargeable Battery Manufacturers: Chemistry, Strategy, Success.