Half-released with no fire history… Battery quality responsibility increases
The electric vehicle fire that occurred in the underground parking lot of an apartment in Cheongna-dong, Seo-gu, Incheon on August 1 had a huge impact on our society. The entire nation was shocked by the fact that electric vehicles, which are considered to be cutting-edge, future-oriented devices, could become ‘time bombs’ that can cause disaster-level damage in an instant. As ‘electric vehicle phobia’ spread and consumers’ attention turned to information on electric vehicle batteries, 10 domestic and foreign automakers and importers disclosed the batteries installed in their 86 electric vehicles. However, ultimately, there is a point that information regarding what electric vehicle batteries have caught fire and which batteries are vulnerable to fire should be clearly disclosed.
Evolved in 8 hours and 20 minutes
Electric vehicle fires occur differently from internal combustion engine fires. According to the National Fire Agency, the number of electric vehicle fires per 10,000 vehicles last year was 1.3. Although the frequency of fires is lower than that of internal combustion engine vehicles (1.9), it is not a cause for concern. This is because electric vehicle fires can reach temperatures of over 1,000 degrees in a short period of time due to the phenomenon of “thermal runaway.” Since electric vehicle battery packs are waterproof and dustproof, fire extinguishing is difficult, so the damage can increase exponentially. According to the National Fire Agency, the average property damage per electric vehicle fire from 2021 to 2023 is 23.42 million won, which is 2.5 times that of internal combustion engine vehicles (9.52 million won).
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The electric car fire in Cheongna, Incheon took 8 hours and 20 minutes to be extinguished, burning down 72 cars in the underground parking lot and causing damage to apartment facilities and pipes. Five days later, an electric car fire broke out in a public parking lot in Geumsan-gun, Chungcheongbuk-do, raising concerns about the issue. The fire was extinguished in 1 hour and 37 minutes, preventing further damage. Moon Hak-hoon, a professor at Osan University’s Department of Future Electric Vehicles, said, “It is highly likely that the fire was caused by a short circuit inside the battery,” but added, “We need to wait and see until the details are revealed.”
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As electric vehicle phobia spread, automakers began to disclose the manufacturers of the batteries used in their electric vehicles. As of August 14, three domestic automakers (Hyundai Motor Company, Kia Motors, and KG Mobility) and seven imported car companies (Benz, BMW, Volkswagen, Stellantis, Polestar, Audi, and Lexus) had joined the disclosure procession (see Tables 1 and 2). The Mercedes-Benz (EQE 350+) that recently caught fire was equipped with a Chinese Farasis battery, and Kia (EV6) used an SK On battery. Farasis has a history of being involved in electric vehicle fires in the past. In 2021, China’s Beijing Automotive Group (BAIC) recalled about 30,000 electric vehicles due to concerns about battery fires, and the batteries in question were manufactured by Farasis. It was revealed that Mercedes-Benz used Farasis products in many of its electric vehicles.
The number of fires is small, but the damage is extensive.
Among the various electric vehicle batteries, are there any models that are vulnerable to fire? Electric vehicle batteries can be largely classified by two criteria. Based on the material that makes up the cathode material, they can be divided into NCM (nickel cobalt manganese) and LFP (lithium iron phosphate) batteries, and based on the form factor, they can be classified into pouch, square, and cylindrical types. Since each type has its own advantages and disadvantages, battery manufacturers combine them to make batteries as needed. Typically, NCM batteries are more vulnerable to fire than LFP batteries, and pouch batteries are more vulnerable to fire than square and cylindrical batteries.
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The recently burned Mercedes-Benz EQE 350+ and Kia EV6 are also known to have used ‘pouch-type NCM batteries’. These are models known to be relatively vulnerable to fire in each classification group. NCM batteries can increase the energy density as the nickel content increases, which can increase the driving range of electric vehicles, but at the same time, there is a problem of being vulnerable to battery fire. Pouch-type batteries have the advantage of being able to fill the battery according to the shape of the electric vehicle, but they are relatively vulnerable to thermal runaway.
“No electric vehicle fire data, difficult to compare”
However, there is also a point that “we should not assume that NCM batteries are vulnerable to fire.” This is because verification is difficult since specific data on electric vehicle fires has not been released. Professor Lee Ho-geun of Daedeok University’s Department of Future Automotive Engineering said, “LFP batteries are more heat-resistant, so they are advantageous in preventing the spread of fire,” but added, “It is difficult to simply compare the stability of NCM and LFP batteries in a situation where data based on fire cases has not been released.”
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Another factor that makes verification difficult is that Chinese battery companies mainly produce LFP batteries, while domestic battery companies produce a lot of NCM batteries. Professor Lee added, “The fact that information on the defect rate or fire occurrence rate of Chinese batteries, which produce more than half of the batteries in the world, is not transparently disclosed also makes it difficult to compare NCM batteries and LFP batteries.”
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The timing of the battery failure also makes it difficult to diagnose the problem. This is because the approach to solving the problem varies depending on whether the electric vehicle fire was caused by a battery design problem, a manufacturing problem, or a vehicle management problem. Generally, NCM batteries may have a higher fire risk, but this can vary greatly depending on the manufacturer. Professor Lee said, “We need to minimize the failure rate during the battery manufacturing process, but at the same time, we need to properly equip parking lots with fire suppression devices or strengthen the battery management system (BMS) to minimize fire damage.”
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The industry’s responsibility for battery quality assurance and safety is expected to increase due to the series of electric vehicle fires. As social demands for battery information disclosure increase, automakers will demand a higher level of quality from battery manufacturers.
Can we kill two birds with one stone: cost and safety?
There is a point that ultimately solid-state batteries should be used to reduce electric vehicle fires. Solid-state batteries are batteries that replace the flammable liquid electrolyte between the positive and negative electrodes with a non-flammable solid electrolyte. Thanks to this, they have the advantage of lower fire risk than existing batteries. Professor Moon Hak-hoon said, “Both NCM batteries and LFP batteries use electrolytes, making them vulnerable to impacts, etc.” “Since these batteries cannot be free from fire, using solid-state batteries can also reduce the risk of fire.” Professor Kang Byung-woo of POSTECH’s Department of Materials Science and Engineering said, “The biggest problem is the high cost,” but added, “Ultimately, we need to move in this direction because using solid-state batteries can increase the energy capacity of the battery while reducing the risk of fire.”
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〈This article Weekly Donga 〉Published in issue 1453
Reporter Jinryeol Choi, Weekly Donga, [email protected]
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2024-08-17 22:29:35