Forensics is underway for the Mercedes-Benz EQE fire that occurred in South Korea on August 1. However, it is very difficult to forensically examine the vehicle and the battery area that was consumed by the fire and will not be able to come to a proper conclusion, local media reported.

Many industry battery experts and others have suggested that there may have been a major problem in the construction of the Mercedes-Benz EQE’s battery pack. The Mercedes-Benz EQE 350+ that caught fire has a battery capacity of approximately 88.8 kWh. It contains 360 NCM811 pouch cells made by Farasis of China, divided into 10 modules, with 36 cells per module. This module has a high capacity of 8.88 kWh per set of modules.

Normally, when a battery ignites, it starts to burn with sparks, but rather than causing a large explosion, the process is for the fire to rise all at once and then burn. In the case of the EQE fire, however, if you look at the video at the time of the fire, an explosion that looked as if it swallowed an entire vehicle occurred within about 20 seconds of the smoke coming out. Generally, 1) the process of ignition → explosion tends to accelerate if the cell capacity of each module is too large, and 2) if the capacity of each module is large, it is necessary to take measures to prevent heat diffusion, shield heat, and block air flow in case of emergency, in addition to the usual cooling materials between the cells. However, no such structure was found in this EQE, and only aluminum cooling plates were inserted between the cells. In a sense, this shows how the EQE was built while keeping costs down, but I felt that this alone was not enough to prevent not only thermal runaway but also fire.

On the other hand, there was a fire accident of Kia EV6 in Korea at the same time. It took about 19 minutes from the time the smoke started to the time it ignited. It looked more like a “fire” than a large explosion. The car was towed out of the underground parking lot by a tow truck and the fire was extinguished outside. What made these things possible was the way Kia makes its battery packs: the Kia EV6 has a battery capacity of 84 kWh, but with 32 modules, which is about 2.6 kWh per module. It is difficult to show a direct correlation between module capacity and combustion power in a simple way, but we speculate that if a cell were to go into thermal runaway and catch fire, the amount of energy the battery cell would have would change the combustion power generated. In addition, we believe that safety can be improved by physically separating the cells by modularizing them into smaller pieces. In recent years, various low-cost technologies such as Cell to Pack and Cell to Body have been introduced, but we still need to create safe battery packs in case of fire or other accidents.

The world’s major car makers are thinking of BEVs, especially battery packs, on a “cost” basis. The reason is that BEVs are not profitable. However, in order to increase the spread of BEVs in the future, we should consider a safer way to make BEVs. It is important to think about the cost, but how to make a safe BEV is also important, while the image of each automobile company such as “brand” is considered important.