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The self-ignition of electric vehicles "the tip of the iceberg

The self-ignition of electric vehicles "the tip of the iceberg

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  The fundamental reason is that power battery manufacturers and car companies do not pay attention to safety. In order to reduce costs, the quality control of batteries is not strict, BMS design requirements are too low, and there is no adequate safety design protection for power battery packs.
  The electric car is "fire".
   Following the spontaneous combustion incident in Tesla, Weilai and BYD in April this year, Tesla and Weilai successively suffered security incidents in May. The safety issue of electric vehicles has become the focus of social attention. Although the above accidents have not caused any casualties, they have caused consumers' distrust and panic about electric vehicles.
  "The specific reasons are yet to be investigated, but this will undoubtedly sound the alarm for the ternary lithium battery that pursues the energy density. If the winter driving mileage of the pure electric vehicle is attenuated or a customer satisfaction problem, the successive spontaneous electric vehicle spontaneous combustion accidents will occur. It is a potential safety hazard, and with the increase in the number of electric vehicles, it is more likely to become a hidden danger of social public safety in the future.” On May 17, an industry expert told the 21st Century Business Reporter about the frequent fires in recent electric vehicles. Said.
  In fact, Tesla, Weilai and BYD have had five accidents in China, just the tip of the iceberg that surfaced. According to the incomplete statistics of the public information, with the increase in the number of possessions, the fire accidents of electric vehicles in China have increased year by year in the past few years. According to the statistics of relevant departments, there were more than 40 electric vehicle fire accidents in the country in 2018. According to the statistics of the charging pile company's special call statistics, the number of electric car fires has reached 11 from April 21 to May 10.
  On the one hand, the power battery is constantly pursuing higher specific energy and greater charging rate, resulting in increased safety risks; on the other hand, the early immature new energy vehicles have entered the high-risk period after running for several years. Calmly thinking about the fast-developing electric vehicle industry in the past decade, the most basic problem of battery safety is still the most important threshold and must be highly valued.
  The cause of many accidents is unknown.
  For the electric car fire accident, the major car companies quickly gave a simple description of the event. However, among the five accidents that caused strong concern in the near future, only Wei Lai gave the specific reason why the ES8 repaired in Xi'an caused fire.
  On the evening of April 21, a Tesla Model S parked in an underground garage in Shanghai spontaneously exploded and ignited a number of vehicles along the side. On April 22nd, at the Weilai authorized service center in Xi'an, a repairing ES8 burned. Wei said that the accident vehicle had suffered a serious impact from the previous chassis, resulting in a large area of ??the left rear casing and cooling plate of the power battery pack. Deformation. The internal structure of the battery pack forms a short circuit after being squeezed for a period of time, eventually causing a fire. On April 24th, a BYD e5 fire broke out on the streets of Wuhan. The BYD official said that after the initial inspection, the fire point was at the trunk of the vehicle and the power battery was in good condition.
  On May 12, a Tesla Model S in a parking lot in Hong Kong ignited spontaneously and exploded three times. At 18:16 on May 16, a Weilai ES8 suddenly smoked in the underground garage of a residential area in Jiading District, Shanghai. The firefighters spent two hours before putting them out.
  Among the above five accidents, Wei Lai’s attitude was more positive and gave the preliminary investigation reasons, but Tesla has not yet given a detailed explanation of the accident investigation.
  In fact, the reasons for analyzing the fire of electric vehicles are more complicated. The Defective Product Management Center of the State Administration of Markets has said that the investigation of defects is very much in view of the fact that the fire of electric vehicles may be related to electrical wiring, fuel cells, mechanical interference and external fire sources, and some evidence will disappear or change during the combustion process. Difficulties, the cause analysis is extremely complicated.
  However, in the industry's view, the battery is the main cause of fire in electric vehicles. "First, when the battery is being charged, it is easy to have an accident due to short circuit or improper operation. Second, after a traffic accident such as a collision of an electric vehicle, there may be a problem with the internal structure of the battery, and there is a hidden danger of spontaneous combustion; in addition, summer temperature Excessively high or long-term high-speed operation of the battery may also cause battery safety failure." On May 19, an industry expert said in an interview with the 21st Century Business Herald.
  However, the above-mentioned experts said that the pursuit of high energy density is the main reason. Under the guidance of subsidy policy and the promotion of competitiveness through high endurance, the relevant enterprises in the industrial chain are too pursuing energy density. Have enough time to do security verification. At the same time, it has to face the pressure of cost and price, and it is cheap to use materials, which does not guarantee sufficient security.
  A recognized fact is that the higher the energy density of the battery material, the higher the safety risk. "From the material system, the constant pursuit of high energy density is not wrong, but the safety risk is indeed high. Tesla represents a relatively high level in battery design and battery, and there are still some problems, which means that A battery with high energy density does have a risk of thermal runaway," said a battery expert.
  Some enterprises have taken relevant measures for frequent fire incidents.
  On May 15, Tesla officially announced the upgrade of BMS software to adjust the "charge management and thermal management settings" to further protect the car battery and extend battery life. Tesla emphasizes that the Tesla battery pack is designed with the most advanced technology, only in very rare cases, and the fire spreads very slowly, giving passengers enough time to leave the car to ensure safety.
  Although the fire results of Weilai ES8 Shanghai on May 16 have not yet announced the results of the investigation, Shen Fei, vice president of Weilai Automotive Energy, said that the accident vehicle was parked for 4 days under the state of the gun. After the battery was fully charged, the system automatically recharged several times. The battery will remain fully charged for a long period of time. In view of the fact that the probability of failure of the power battery in the state of long-term high power will increase, due to the principle of safety and prudence, before the official investigation results, the exclusive piles and vehicles in the connected state will be Temporary measures will be taken to limit the amount of charge to 90%. However, he also stressed that this move does not mean that the accident is caused by charging.
  The whole industry chain is ringing the alarm
  Concerns about the spontaneous combustion incident, Tesla CEO Elon Musk said that the media over-exaggerated the Tesla spontaneous combustion incident, but turned a blind eye to thousands of fuel vehicles every year, which is undoubtedly a double standard. The fuel car fires at a much higher frequency than the Tesla car, even Tesla.
  However, the problem of fire in electric vehicles cannot be ignored. In many cases, electric vehicles are sudden and unpredictable fires, and the fire is fast, the temperature is high, the spread is fast, and the explosion is easy. Once the car is burned, it cannot be quickly saved, and it is easy to ignite and burn the surrounding vehicles. The damage caused is huge.
  On the whole, the direct cause of the fire in electric vehicles may be thermal runaway. However, the fundamental reason is that power battery manufacturers and car companies do not pay attention to safety. In order to reduce costs, the quality control of batteries is not strict, the design requirements of BMS are too low, and there is no adequate safety design protection for power battery packs.
  As for the electric vehicle power battery, the selection of the battery core, the design of the battery pack, the BMS thermal management system, and the safety protection are all key factors affecting the safety of the electric vehicle. The energy density of the battery and battery is proportional to the cruising range. The greater the power, the longer the battery life. However, the security risks that come with it are higher.
  There is a view that the reason why Tesla frequently caught fire is mainly because Tesla's high-density cylindrical batteries are more likely to increase the energy density of the battery. Most companies choose a square battery, and the cruising range cannot reach the height of Tesla.
  At present, most car companies are still advancing to high endurance, one of which is to improve the cathode material of the battery. At present, the ternary lithium battery mainly used in electric vehicles in China, the higher the proportion of nickel, cobalt and manganese in the positive electrode material, the higher the energy density of the battery. At the same time, reducing the cost of expensive cobalt can also reduce costs. At present, the mainstream batteries in the market are NCM523 and NCM622 (the ratio of nickel-cobalt-manganese is 5:2:3 and 6:2:2 respectively). The newly-launched AION S of GAC New Energy is equipped with the NCM811 battery produced by Ningde Times, which makes it The cruising range can exceed 600 kilometers, which is also the first production model to use the NCM811 battery.
  However, the industry still has some doubts about the battery safety of the NCM811. “Because the proportion of nickel is too high, it is easy to cause problems such as decreased safety performance, reduced charging efficiency, overheating, etc. in production. The conditions for producing batteries are also very strict. The safety requirements are much higher than before.” When applying new battery technology, car companies must ensure adequate verification and security.
  An insider of the Ningde era said that NCM811 batteries in Ningde era have been designed with multiple safety features from cell safety, module safety to battery pack safety. The Ningde era conducted 273 battery tests, including 100 performance tests, 48 ??safety tests, and 125 reliability tests.
  A number of auto industry insiders told 21st Century Business Herald that the excessive pursuit of energy density left a hidden danger to the safety of electric vehicles. With the increase in sales of electric vehicles in China, similar fire accidents will increase, which means that more secure safeguards are needed.
  According to Wang Binggang, a new energy vehicle expert, electric vehicles can be done very safely. "Last year, I went to Nissan to know that Nissan sells nearly 500,000 vehicles (electric vehicles). There are no fire accidents. Their safety standards and test methods are extremely demanding. I think that the internal self-ignition is unpredictable and unacceptable." Wang Binggang said .
  Ouyang Minggao, executive vice president of the Electric Vehicle Hundred People Association and academician of the Chinese Academy of Engineering, once said that according to his investigation and analysis, the fire accident of electric vehicles with high incidence in the first half of last year, although there are series of reasons such as verification and testing, the main reason is that the battery is out of control. . He has appealed to related companies in the industry chain to strengthen technology research and development and investment, to respond with advanced BMS and heat spread prevention methods, and to provide early warning technical interventions for short circuits inside the battery. At the same time, he also proposed that the annual safety inspection specifications for electric vehicles should be introduced as soon as possible. However, Yu Qingjiao, chairman of the Zhongguancun New Battery Technology Innovation Alliance and chairman of the Battery Hundred People Association, said that considering the cost factor, car companies are not motivated to carry battery safety products.
  Frequent spontaneous combustion events have caused growing new energy vehicles to face many challenges and challenges. At present, it is still in the market cultivation period, and self-ignition will also make consumers lose trust in electric vehicles, especially for new companies such as Tesla and Weilai, which are selling at a higher price, which is greatly damaged by their brands.
  "Before the delivery of the new car, we must do a good job of quality control, and thoroughly test the battery and the safety of the vehicle. Battery manufacturers and OEMs should strengthen their own research and development, do not leap forward, but put safety first, steadily Improve the technical level." The above-mentioned automotive industry people finally said.