Why is the electric car not equipped with a ternary lithium battery?

Zhang Xiangmu, director of the Equipment Industry Department of the Ministry of Industry and Information Technology, said at the 2016 China Electric Vehicle Hundred People Forum that the suspension of the ternary lithium battery bus was included in the “Recommended Model Catalogue for New Energy Vehicle Promotion and Application”, which expressed the country’s concern about the safety of the power battery. In fact, on January 14 this year, the new car catalogue of the Ministry of Industry and Information Technology has no passenger car products equipped with ternary material batteries.

The reason given by Zhang Xiangmu is that the ternary lithium battery has higher specific energy and better cycle performance, which is an important development direction of lithium batteries in the future. However, China started late in this field, and the safety development and verification of the products for passenger cars is not enough. The Ministry of Industry and Information Technology is considering further improving the safety technology threshold for new energy vehicle products, and organizing risk assessments for vehicles such as ternary lithium battery buses under the current safety standard system. He made it clear that before the evaluation was completed, the suspension of the ternary lithium battery bus was included in the “Recommended Model Catalogue for New Energy Vehicle Promotion and Application”.

The ternary material is flammable at high temperature

The safety risks of ternary materials are relatively large. Huang Xuejie, a researcher at the Institute of Physics of the Chinese Academy of Sciences, said that in summing up the experience of previous accidents, the nickel-cobalt-aluminum ternary material 18650 batteries will self-heat above 180 °C, which is difficult to control after fire, and the lithium iron phosphate material is above 250 °C. There will be an exothermic phenomenon and the safety is relatively high.

In terms of material properties, both materials will decompose when they reach a certain temperature. The ternary lithium material will decompose at about 200 °C, and the lithium iron phosphate will decompose at 700-800 °C. Moreover, the chemical reaction of the ternary lithium material is more intense, and oxygen molecules are released, and the electrolyte rapidly burns under the action of high temperature, and a chain reaction occurs. Lithium iron phosphate does not release oxygen molecules when it decomposes, and the combustion is not as intense. Therefore, the ternary lithium material is more likely to catch fire or cause an accident than the lithium iron phosphate material only from the characteristics of the positive electrode material of the lithium ion battery.

Battery capacity leads to poor heat dissipation

In addition to the safety risks of ternary materials, the passenger battery capacity is larger, which also increases the risk of ternary batteries. Huang Xuejie said that battery safety is inversely proportional to the energy stored in the battery t he greater the energy that can be released, the greater the safety risk. The battery capacity of pure electric cars is generally several tens of kilowatt-hours, while pure electric buses the battery capacity is up to several hundred kilowatt-hours. As the battery capacity increases, the battery volume also increases, and its heat dissipation performance deteriorates, and the possibility of a safety accident increases.

Huang Xuejie told reporters that the lithium-ion battery should be used as a power battery, and its safety performance must be improved. The larger the single battery, the higher the safety index required. In addition, the safety of the battery system is not determined solely by the single battery. Liu Yanlong, secretary general of the China Chemical and Physical Power Industry Association, believes that the group technology, charging method, usage method, maintenance method, reliability of the protection system, and the effectiveness of the communication protocol of the electric vehicle battery pack will all contribute to the safety of the battery pack influences.

Lack of evaluation system

It is because of the lack of a corresponding evaluation system in China that it is difficult to assess the final safety situation of the ternary battery system. The battery packs will be designed according to the conditions of the vehicle. By strengthening the monitoring of the whole process, the safety of the ternary battery system can be effectively improved. However, the final safety is determined by the corresponding evaluation system. Liu Yanlong told the reporter. "There is no corresponding evaluation system in China."

Wang Binggang, a special expert in the special technology of electric vehicles for the Ministry of Science and Technology, agrees with Liu Yanlong. Wang Binggang believes that the choice of battery materials can not fundamentally solve the battery safety problem, should start from the development of strict battery product quality requirements and regulatory measures. In this regard, Wang Binggang put forward two suggestions. First, it is necessary to set clear safety assessment indicators for battery modules and battery systems. Second, strict monitoring of new energy buses should be carried out to clarify monitoring contents and responsibilities.

Qi Yiliang, the marketing director of AVIC Lithium (Luoyang) Co., Ltd. believes that the bus operation route and environment are relatively fixed. The battery power is not the focus of passenger cars. It should adhere to the lithium iron phosphate route with higher thermal stability and safer safety. The data shows that among the pure electric buses produced in China, the passenger cars using lithium iron phosphate power batteries account for 60% of the total new energy bus market, and the ternary material power batteries account for 30% of the market share. Lithium iron phosphate batteries are still the mainstream of the electric bus field and are also the best choice.

The page contains the contents of the machine translation.