According to media reports, on June 13, a Huawei mobile phone store in Ordos, China caught fire. The cause was a Wenjie M5 exhibition car parked inside. On June 12, a BYD Song caught fire when it was parked in Zhuhai. A week ago, on June 6, three electric vehicle fires occurred on the same day in Wuhan, Hubei, Foshan, Guangdong, and Guigang, Guangxi. Recently, a hit Tesla in the United States suddenly caught fire after being parked in wasteland for 3 weeks...
Some of these incidents occurred when the vehicle was parked and charged, some were "sequelae" after the vehicle was hit, and some caught fire inexplicably during normal driving.
Data from the Fire and Rescue Bureau of the Ministry of Emergency Management shows that in the first quarter of 2022, a total of 640 new energy vehicle fires were reported in China. Compared with the same period last year, this figure has increased by 32%, which means that there are more than 7 new energy vehicle fires on average every day.
It seems that electric vehicles are very unsafe.
However, as an objective comparison, according to the data of the Passenger Federation, the cumulative wholesale sales of the domestic new energy passenger vehicle market in the first quarter of 2022 reached 1.19 million units, a year-on-year increase of 145.4%. Although the absolute number of new energy vehicle fire cases is on the rise, if the rapid growth of new energy vehicle sales is taken into account, the proportion of fires actually declined.
Electric car fires are less likely, but harder to put out
U.S. website AutoinsuranceEZ based its statistics on data from the National Transportation Safety Board (NTSB), the Bureau of Transportation Statistics (BTS), and government recall data from Recalls.gov. There will be only 52 electric vehicle fires in the U.S. in 2021. For comparison, there were 16,051 fires involving hybrid vehicles and 199,533 fires involving gasoline-powered vehicles in the U.S. over the same period.
Comparing only absolute values, however, is inaccurate, as there are far more gasoline-powered cars on the road than electric cars.
But even compared with the number of fires of 100,000 vehicles, the number of fires of fuel vehicles was 15.299 per 100,000 vehicles, which was lower than the 34.745 per 100,000 vehicles of hybrid vehicles; while the number of electric vehicles was the least, only 25.1 per 100,000 vehicles. 10,000 vehicles.
According to a recent report by the National Fire Protection Association (NFPA), vehicle fires accounted for 15 percent of the 1.4 million fires in the United States in 2020, resulting in 18 percent of civilian deaths and 11 percent of civilian injuries. Electric vehicle fires account for about 0.02 percent of all U.S. fires.
Collision is the leading cause of electric vehicle fires. According to the National Fire Protection Association, an estimated 560 people will die in car fires in 2020, most of which are caused by collisions.
Although electric vehicles are less likely to catch fire, a problem that cannot be ignored is that battery fires are more difficult to put out than gasoline fires.
The water consumption for extinguishing a burning fuel vehicle is about 1 ton, while the water consumption for extinguishing an electric vehicle ranges from a dozen to 100 tons. According to public information, in April this year, a Tesla Model S collided and caught fire in the United States. It took firefighters 7 hours to put out the fire, consuming 106 tons of water.
The main reason for this is the high resurgence rate. The NTSB pointed out that after the thermal runaway of the lithium battery in an electric vehicle, it does not release all the energy in an instant, but gradually spreads to the surrounding battery cells as the heat spreads. As a result, extinguishing and re-ignition will occur.
The agency said that according to its calculations, a lithium battery fire can reignite up to 15 times.
In the case of the BYD Song model fire on June 12, according to media reports, when a security guard tried to put out the fire with a fire extinguisher, the vehicle continued to make explosive sounds. The conventional judgment is that thermal runaway continues to spread and transmit in the battery pack.
To sum up, in the current market, there may be only a very small number of electric vehicles that have quality and safety problems, but once a problem occurs, the consequences may be more serious. In order to be as foolproof as possible, car companies still need to spend a lot of effort.
Car companies turn to lithium iron phosphate batteries
In the past 10 years, the cruising range of new energy vehicles, especially pure electric vehicles, has experienced a breakthrough from 100 kilometers to 1,000 kilometers. Behind this is the transformation of the technical route from lead-acid batteries, to lithium iron phosphate batteries, to ternary lithium batteries.
But now, automakers are turning back to lithium iron phosphate batteries.
From a safety point of view, ternary lithium batteries are more active, while lithium iron phosphate batteries have higher thermal stability, so lithium iron phosphate batteries are relatively safer. This may partly explain why the rate of electric vehicle fires is declining.
According to foreign media reports, South Korean battery giant LG New Energy plans to start mass production of standard-sized lithium iron phosphate batteries in October 2023. In this regard, Mo Ke, chief analyst of True Lithium Research, mentioned in an interview with the media that LG announced the mass production of lithium iron phosphate batteries. On the one hand, the reason is that the ternary lithium batteries used by LG in the Korean energy storage market have been frequently used in the past year or two. There is an accident, so I am considering whether lithium iron phosphate is more suitable for energy storage.
In 2020, the domestic Tesla Model 3 standard battery life version will be equipped with lithium iron phosphate batteries; in 2021, the domestic Model Y standard battery life version will use lithium iron phosphate batteries. At the end of 2021, Tesla said that the standard battery life versions of Model 3 and Model Y worldwide will be switched to lithium iron phosphate batteries.
In March last year, the Xpeng P7 lithium iron phosphate model was launched; in April, BYD announced that its pure electric models began to fully switch to lithium iron phosphate blade batteries. In addition, some A00-class new energy models, including Great Wall Euler and Wuling Hongguang MINI EV, have begun to carry lithium iron phosphate batteries; Volkswagen, Ford, and Mercedes-Benz also claim to use lithium iron phosphate batteries on entry-level models.
According to the data of China Automotive Power Battery Industry Innovation Alliance, in July 2021, the monthly loading of lithium iron phosphate batteries exceeded that of ternary batteries for the first time. The loading volume of lithium iron phosphate batteries in this month was 5.8GWh, and the loading of ternary batteries was 5.8GWh. The amount is 5.5GWh. By April this year, the installed capacity of lithium iron phosphate batteries reached 8.9GWh, accounting for nearly 70% of the total installed capacity in the market, while the installed capacity of ternary lithium batteries was 4.4GWh, accounting for 32.9% of the total installed capacity, a year-on-year decrease of 15%. .
Although the original intention of car companies to turn to lithium iron phosphate is to reduce costs, avoiding expensive nickel and cobalt in ternary lithium batteries also indirectly improves safety.
Battery pack technology is improving
Of course, car companies are also constantly exploring ways to directly improve battery safety.
For example, GAC Aian's "magazine battery". In March 2021, Liu Shiqiang, chief expert of China Automotive Technology Research Center, led a team to conduct acupuncture tests on ternary lithium battery packs using magazine battery technology. After acupuncture, the battery pack only smoked for a short time (about 1 minute), and there was no fire or explosion. After standing for 48 hours, the voltage dropped to 0V, the temperature returned to room temperature, and the internal structure of the battery pack was intact. Only the acupuncture cell module experienced thermal runaway, which did not spread to other cells.
In the acupuncture experiment on lithium iron phosphate battery packs, the voltage dropped and the temperature rose after the acupuncture of ordinary lithium iron phosphate battery packs triggered thermal runaway. The maximum temperature reached 329.4°C, and smoke continued for 16 minutes. The iron-lithium battery pack has a maximum temperature of 51.1 ° C after being stabbed, and there is no smoke, fire and explosion. After standing for 48 hours, the cell voltage dropped to 0V, the temperature dropped to room temperature, and the internal structure of the battery pack was intact after opening the battery pack.