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Tesla, Weilai, ideal Why do newly built cars love spontaneous combustion?

via:博客园     time:2020/5/19 14:19:58     readed:68


Original by ID:rancaijing

By Zhou Jifeng

Editor Jin Yu

Auto ignition and fire of new energy vehicles are not new topics for a long time, but this time, new players have been added.

An ideal new-energy car caught fire ONE its engine compartment on the streets of Changsha, Hunan province, on May 8. According to live video circulated online, the accident in front of the engine room smoke and fire phenomenon, after the fire was extinguished, the front face of the vehicle and the front cover almost all burned, fortunately no one was injured.

After the event, the official microblog of ideal automobile quickly responded: after on-site inspection, there was no problem with the vehicle battery system. At present, the vehicle has been moved to a safe area for inspection, and subsequent investigation results will be released in time.

At the ideal official APP, the owner replied that the preliminary determination of the cause of the fire is not a range booster and oil problems, nor battery problems, waiting for follow-up investigation.

The relationship between the spontaneous combustion and the battery was cleared for the first time. This is not surprising. In recent years, spontaneous combustion incidents of new energy vehicles are common, many of which are caused by batteries.

Under the background of the domestic new energy vehicle subsidy policy, the new energy vehicle sales all the way to the song. According to the statistics of the national big data alliance of new energy vehicles, the number of new energy vehicles in the country reached 3.81 million by the end of 2019, accounting for 1.46 percent of the total number of vehicles, and the increment of new energy vehicles exceeded 1 million for two consecutive years, showing a rapid growth trend.

Some insiders said that the endurance mileage, power and configuration have become the focus of consumers and businesses, while the safety aspect has not been paid attention to. On the other hand, new energy vehicles have frequent safety incidents.

According to the big data safety supervision results report of the national regulatory platform for new energy vehicles, since may 2019, the national regulatory platform for new energy vehicles has found a total of 79 new energy vehicle safety accidents, involving 96 vehicles. Among them ,47 accident vehicles have been connected to the national regulatory platform ,28 accidents in the first 10 days of the national regulatory platform has been early warning.

For car companies, the safety risks of new energy vehicles have become a short board restricting their development. Last year, for example, because of a number of spontaneous combustion incidents, Wei Lai had to recall 4803 vehicles, heavy losses, Tesla also repeatedly due to domestic and foreign spontaneous combustion incident shares fell.

This time, the ideal car self ignited, once again pushing new energy vehicles to the forefront of the wave. People have to re-examine the quality and safety of new energy vehicles. Why are new energy vehicles always self igniting? Is there any safety guarantee for purchasing new energy vehicles?

There are three reasons for the spontaneous combustion of new energy vehicles

From the spontaneous combustion events of new energy vehicles since 2019, Burning Finance selected 18 cases with clear disclosure information as samples. Brand, the new domestic car-building forces, Wei Lai car fire occurred many times; the leader Tesla is not immune, the biggest fermentation is Tesla

In terms of battery types, quite a number of accident vehicles are equipped with ternary lithium batteries; in terms of the state when the accident occurred, there are four in driving state, accounting for about 22%, five in charging state, accounting for about 28%, seven in static state, accounting for about 38%, and two in unknown state. In addition, most of the spontaneous combustion accidents occur in summer; the accidents of passenger cars are much higher than those of special cars.


Cartography / fuel Finance

As Liu Peng, an associate professor at Beijing Institute of Technology and deputy secretary-general of the National Big Data Alliance for New Energy Vehicles, also demonstrated in a micro-classroom sharing, the charging process, the static state after being charged are the main components of the fire accident, and most of the new energy vehicle safety accidents occur the State of Charge (SOC)

Specific to the cause of the accident, Cui Dongshu, Secretary General of the China Federation of passenger transport, said to the fuel economy department that there are mainly the following situations in the spontaneous combustion of new energy vehicles:

First, when the car chassis collides, the electric core or high-voltage device in the internal battery pack is squeezed or punctured, and other components in the battery pack also have the risk of short circuit or even fire and explosion in the collision, which is easy to cause fire.

Take an es8 accident in Weilai on April 22, 2019 as an example. An es8 in Xi'an under repair suddenly caught fire. The investigation results show that the left rear shell and cooling plate of the power battery pack were deformed in a large area due to the severe impact on the chassis of the accident vehicle.

Then, in a short period of time, the spontaneous combustion occurred in Yuli. At last, through the investigation of Weilai and the expert group, it is found that the reason for the defect of the vehicle is that there is a problem in the internal wiring direction of the power battery module, which causes the friction between the harness and the battery frame and is squeezed by the cover plate. In extreme cases, the insulation layer of the circuit will be worn, resulting in a short circuit and out of control fire after overheating.

For this reason, we have to recall 4803 vehicles of our es8 electric vehicle equipped with the power battery pack produced from April 2 to October 19, 2018.

Secondly, the lack of thermal management in the early stage of the battery, coupled with the high internal temperature in the high temperature season, is easy to cause the battery heat out of control.

For example, in March 2019, there were several spontaneous combustion events of BAIC Weiwang 407ev in Shenzhen. According to the accident, a group of 43.5kwh ternary lithium batteries used by BAIC Weiwang 407ev had quality problems, which led to frequent thermal runaway events.

Third, it is also the most common case, that is, during the charging process of the new energy vehicle battery, especially under the fast charging mode, the battery risk increases.

At present, the power batteries of electric vehicles are mainly lithium batteries, which are divided into lithium manganate, lithium iron phosphate, lithium nickel cobalt manganate, lithium cobalt carbonate, etc. Among them, the density of lithium iron phosphate is poor, the endurance is low, and the application is few; the cycle life and energy of lithium manganate are low, so it is not suitable for power vehicles. At present, the most favored battery for electric vehicle enterprises is the nickel cobalt lithium manganese acid battery, namely the ternary lithium battery. The energy density is higher than that of lithium manganese acid, which can reach 200-300wh / kg, and the driving range is longer.

The ternary lithium has high endurance, high energy density, high activity, but also easy thermal failure.

Wang Pengbo, a senior expert in the field of new energy vehicles, told the book,

There are holes behind the high endurance

Compared with 2017, the subsidy policy in 2018 has raised the threshold of endurance mileage, battery energy density and energy consumption level. For example, the threshold of mass energy density of power battery system has been raised from 90Wh / kg to 105wh / kg, and the threshold of endurance mileage has been raised from 100km to 150km. In other words, models with a range of less than 150km will not get subsidies.

In 2019, the subsidy policy further raised the subsidy threshold, and the driving mileage of pure electric passenger vehicles under the working condition method should not be less than 250km, which is increased by 100km compared with the minimum endurance requirement of the previous year; at the same time, the subsidy standard of new energy passenger vehicles, new energy buses and new energy trucks is reduced, and the subsidy decline rate is more than 50%.

Consumers at the other end are also more concerned about mileage. More than one consumer buying or preparing to buy a new energy vehicle told fuel finance that in addition to the license plate, the endurance mileage is the first factor to consider when buying a vehicle.


Source / Vision China

The auto industry analyst Ren Wanfu further said,

Cui Dongshu also revealed that the core cause of the recent series of spontaneous combustion events is

Wang Pengbo also said that the activity of the cell of the ternary lithium battery is indeed great, but the safety is also related to whether there is insulation failure diffusion material between the cells, BMS management strategy of the battery, cable line design, heat dissipation system design, battery shell structure design and vehicle structure protection.

First, in order to improve the endurance mileage, most of the current pure electric vehicles arrange the power battery under the bottom plate. The battery area is large and almost covers the whole bottom plate. The distance from its periphery to the edge of the body is usually not large, so it is easy to be squeezed when it collides or supports the bottom. Secondly, in recent years, the energy density of battery cell has increased too fast, accompanied by the decrease of cell stability, and the risk of thermal runaway under mechanical load has increased. Because the subsidy policy requires the energy density of the power battery system, in order to improve the energy density of the whole package, domestic pure electric vehicles tend to make the shell structure of the battery pack as light as possible, resulting in insufficient protection for internal modules and high-voltage devices.

Can we have both endurance and safety?

On April 23, the Ministry of Finance and other four ministries and commissions issued the notice on improving the financial subsidy policies for the promotion and application of new energy vehicles. The subsidy standards for 2020-2022 will decline 10%, 20% and 30% respectively on the basis of the previous year, and the decline will be reduced. The new deal also revised the range of subsidies for new energy electric vehicles, with subsidies of 16200 yuan for more than or equal to 300 kilometers, 400 kilometers or more, and 22500 yuan for more than or equal to 400 kilometers.

Ren Wanfu told burning finance,

In this context, charging mode has also been called for by some industry to improve. Compared with direct charging, switching mode can be better informed in advance of the safety and use of the battery, but more than one person in the industry said not optimistic about the model.

Among them, Song Jin, an analyst at Analysys, said that the power exchange mode can quickly supplement energy and reduce endurance anxiety, but there is still a big uncertainty at this stage, and the input-output ratio of power exchange is too poor. First of all, the standardization of power battery is not perfect, and the specifications are quite different; second, the sales volume of electric vehicles in 2019 in China is 1.2 million, and the scale of each model is not large, so it is difficult to make profits temporarily.

The core itself has improved. Mr. Wang told SciDev.Net developed

*The picture comes from visual China. At the request of the visitors, Wang Xu is not his real name.

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