Incheon Electric Vehicle Fire Causes Update

[Incheon Electric Vehicle Fire Causes Update]

1. The fire department confirmed that the sprinklers in the underground parking lot did not work. Further investigation will be conducted to determine why they did not work.

If the sprinklers were not working, both the “electric vehicle explosion” and the “no sprinklers in case of fire in the underground parking lot” are important to make things this big. We are concerned that the powder fire extinguisher may have been left unattended because it thought it could be dealt with in the event of a vehicle fire.

2. There is a story that the batteries of the accident vehicle are Farasis energy products, not CATLs.

The battery form factor of parasis is a pouch cell, which is relatively weak against external impact and swelling (battery swelling with gas when the battery is overcharged). The gas vent is not structurally possible, but even a slight swelling occurs, the internal electrode plates are displaced, increasing the possibility of a fine short circuit.

Mercedes-Benz makes its battery packs directly from its subsidiary, and its batteries use CATL and parasitic cells. Some say that European electric cars use CATL cells and other regions use parasitic cells, but the manufacturer will have to check the vehicle number to conclude.

Benz guarantees the performance of any company’s cell, and cell makers and vehicle makers are well aware of the safety issues of pouch cells and are making a lot of improvement efforts.

(The following is a bit of a technicality.)

3. 5-minute thermal runaway delay verification problem
   The NMC811 pouch cell is the most vulnerable to thermal runaway. So, even in Chinese government regulations and international standards, the product is designed and tested to prevent a single cell fire from spreading into a full pack for at least five minutes.

Parasis cells also meet this performance, it says on its website, claiming that fires in China and the United States have “verified thermal runaway delay performance through external agencies” since 2022.

The maker will check whether the car’s battery is a parasitic cell or a CATL cell, but any company’s cell will verify the thermal runaway delay performance with a “new battery.” All batteries have no problem with new performance at all. Over time, the battery degrades and deviations occur, and from then on, the risk increases. The pouch is more vulnerable, but the possibility of thermal runaway with a minimum short circuit due to impact and swelling has to be verified, but this is difficult to reproduce in reality. So in severe cases, we estimate it by simulation and test it with about 5 cells attached as a real test, but it is difficult to say that it is sufficient verification. So many manufacturers focused on increasing capacity and directness, claiming that “our product is safe,” and this was once the case with Korean cell makers, and this trend is strong with Chinese cell makers these days.

It is important to prevent thermal runaway and delay in any company’s batteries, and we are concerned that they are only obsessed with superficial numerical competition and are properly safety-verified. In particular, parasis is a very dangerous claim to advertise that “new technology has achieved high energy intensity and high stability at the same time.”

More practical tests of thermal runaway delay performance are needed.

4. BMS issue
   One battery voltage is between 3.7V and 4.2V, and it is connected in series to raise it to about 1000V and used in electric vehicles. If one cell is connected in series and the other cell has a voltage of 3.9V but is 3.8V alone, this cell operates as a resistor and generates high heat.

That’s why quality control of battery cells is important, and hundreds of cells have to show exactly the same voltage after hundreds of charge and discharge in 0.01V units. It is difficult to avoid deviations between cells, so correcting them is the BMS (Battery Management System). The key to BMS is to continuously measure the voltage between cells and balance them with each other. If 150 cells are 3.91V and 150 are 3.89V, only 3.91V cells are discharged to set the whole to 3.89V.

The BMS is an electronic device and a control board. The durability of the BMS itself and the ability to correct double and triple errors are key to electric vehicle safety. However, since the performance of the BMS is related to the battery cell and closely related to the vehicle design, it is often unclear who is responsible for the performance of the BMS. For car makers, cell makers depend on car makers, which is a vulnerability in safety.

The ideal BMS measures the voltage and temperature of the entire cell 1:1 to over 100 Hz and should be a very robust system with a 20-year performance guarantee against internal control current abnormalities, power losses, and electromagnetic impacts. It is expensive. Electric car manufacturers are concerned about BMS beyond battery capacity and mileage.