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With the integration of the tide of new energy vehicles, nearly 100 new car-building forces have been born in China, and traditional car factories have also accelerated their layout in the direction of new energy. With the support of policies, the new energy vehicle market is beginning to take shape. However, a series of spontaneous combustion and explosion accidents have pushed the safety and stability of new energy vehicle batteries to the tuyere of public opinion.

In April this year, the spontaneous combustion of Shanghai's Tesla garage also ignited other gasoline vehicles near the parking spaces; there were three spontaneous combustion accidents of Lulai cars in two months; and Changan New Energy and Lifan New Energy vehicles also ignited spontaneously in Chongqing in a few days.

High-power and fast charging is the main cause of the recent fire of new energy vehicles, Ouyang Minggao, academician of the Chinese Academy of Sciences, said at the 2019 China (Qinghai) Lithium Industry and Power Battery International Summit Forum.

He also pointed out that the new energy vehicle industry pursues fast charging too much, but the charging algorithm is too simple to ensure safety. It is found that improper fast charging will cause the thermal stability of the power battery to deteriorate and the power battery to decay rapidly. Therefore, our country is considering the formulation of relevant standards for battery thermal runaway.

At present, new energy vehicles have two ways: slow charging and fast charging. Slow charging is generally a household charging pile installed in private parking spaces in the garage, which requires more than 8 hours of charging time. Fast charging uses direct current, the charging power can reach 150 kilowatts, the charge can be charged to 80% in 1-2 hours, and the charging time is also greatly shortened.

Ouyang Minggao said that after studying the batteries of major electric vehicle brands at home and abroad, his team found that the stability of the battery became worse and the temperature at the critical point of thermal runaway dropped significantly after 300-500 times of fast charging, which was an important cause of fire in new energy vehicles. Specifically, the thermal runaway temperature of ordinary new batteries is about 215 degrees, while the critical point of thermal runaway of batteries that use too much fast charge is greatly reduced to 107 degrees, which is more likely to trigger battery thermal runaway and lead to failure and fire.

Ouyang Minggao also gave a set of statistics that in 2018, 29% of new energy vehicle accidents were caused by charging, 14% were caused by spontaneous combustion while driving and at rest, and 10% were caused by water-related fire. the cause of spontaneous combustion of 33% of vehicles is unknown.

The spontaneous combustion incident of Shanghai Tesla garage, which occurred in April this year as soon as possible, has no following, and the cause of spontaneous combustion is unknown, but Ouyang Minggao's report material shows that the Tesla car was driven back to the garage to self-ignite after using super fast charging. The cause of spontaneous combustion may be the spontaneous combustion of "negative pole lithium precipitation" caused by improper charging.

There were also three cases of spontaneous combustion in the past two months. On April 22nd, a NIO ES8 under maintenance in Xi'an NIO Service Center spontaneously ignited until it was burned out, which attracted attention from all walks of life. After the investigation, NIO said the accident was caused by the impact of the vehicle on the chassis before it was sent for repair.

The ES8 in the basement of a residential district in Jiading, Shanghai, was recharged and smoked on May 16. An ES8 spontaneously ignites in a parking lot in Wuhan on June 14.

Sales of new energy vehicles in China will reach 1 million in 2019. Experts predict that the new energy industry will grow by leaps and bounds in 2020, and the number of new energy vehicles is likely to reach 50 million to 80 million by 2025.

"spontaneous combustion" is a very sensitive topic of new energy vehicles at present, and there are a lot of debates on the Internet about "the proportion of spontaneous combustion of new energy vehicles is higher than that of fuel vehicles" or "fuel vehicles are more prone to spontaneous combustion and electric vehicles are safer". The development of lithium battery is a major trend, and the safety of power battery should be fully considered at the same time of rapid development.

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