Yesterday’s article on battery pack sealing sparked discussions in the comment section, with opinions including: the motor system is not entirely sealed, electric cars can short circuit when driven in flooded areas, and long-term water exposure can impact the sealing of batteries, among others. All these viewpoints were valid, as the sealing of the battery pack is not the sole factor affecting electric vehicles after they are exposed to water.
Yesterday’s materials mainly discussed the general situation of battery pack sealing, and today, we would like to share some additional materials on what happens when electric car batteries are submerged in water. Research in this area is mainly conducted within EVS, with sources including China’s research team and Bohyun Moon of the KATRI Institute in Korea.
Research and Case Studies in China
The following are some examples of battery submersion in China:
Case Study 1: In 2016, a bus caught on fire in Nanjing due to a battery system designed according to the IP54 series.
Case Study 2: In 2018, a pure electric vehicle in Guangzhou caught on fire after being submerged in water during heavy rain.
Case Study 3: In 2019, a car caught on fire in Hangzhou due to battery submersion.
In terms of research on the impact of battery submersion, a research team from Tsinghua University released a paper titled “Preliminary Study on the Safety of a Lithium Ion Battery Pack Under Water Immersion.” Additionally, a video was presented at EVS, with the following information:
According to the paper, after submersion, the electrolysis of water inside the battery system creates gas, and the movement of high-pressure gas creates a circuit break that generates arcs at the connection points. If fully immersed, these arcs can result in battery fires. Moreover, when the distance between the positive and negative electrodes of a contactor is relatively close or when the high voltage sampling and collection sections of the centralized BMS are in saline water, circuits can form, such as between the positive and negative electrodes of contactors, between the high voltage sampling segments of BMS, and in the CMU where module collection voltage occurs. When submerged in floodwater, water impurities can easily cause internal erosion in batteries once they are exposed to water.## Testing Cases in South Korea
Like China, labs in South Korea have also conducted some experiments. The first one is removing the battery system housing of KONA EV and directly placing it in water. Here’s the result:
Overall, once it gets wet, the battery slowly discharges its power if the battery design is suitable in terms of distance. It won’t cause a fire. The design that causes a fire doesn’t meet the electrical clearance and creepage distance of its terminals, referring to ISO 6469-1:2019 Electrical clearance and creepage distances.
This group of experiments, especially the case where the clearance of the high-voltage connection is too close, will generate dangerous discharge in the water due to arcing during gas production at 800V.
Regarding improvement on battery pack design, the main thing that can be done is to increase the distance at the module level.
Conclusion: If the distance between the high-voltage connections is designed too close in the BDU, and an outer shell is damaged by a minor accident that cannot be detected in time, once it encounters water, the battery will release a large amount of sparks in the water, and can still catch fire in a submerged state. This is the scene we least want to see. This is also one of the reasons why the battery pack needs to have waterproof requirements.
The good news yesterday was that the heavy rain in Zhengzhou ceased and the water in the city was receding. I hope my friends in Zhengzhou will pay attention to safety and return to normal as soon as possible. Flooded cars should also be sent to the manufacturer for inspection and confirmation in a timely manner, and should not be used casually. This is responsible for the user’s safety.
This article is a translation by ChatGPT of a Chinese report from 42HOW. If you have any questions about it, please email bd@42how.com.