Recently, the Weimar EX5 spontaneous combustion incident continued to ferment, once again pushing the safety of electric vehicles, especially power batteries, to the forefront of public opinion, and this is the second fire incident of Weimar Motors being exposed. With the rapid growth of the number of new energy vehicles in my country, the safety of new energy vehicles should be paid more and more attention.

        The safety of electric vehicles cannot be ignored

         According to public information, Battery China.com found that there were 10 electric vehicle fire accidents at home and abroad in the first half of 2018, including 8 domestic fire accidents and 2 foreign fire accidents, an increase of 1 from the same period last year. In 2013 and 2014, there were 2 and 4 domestic new energy vehicle fire accidents, which directly increased to 14 in 2015, and as many as 29 in 2016. In 2017, publicly reported fire accidents with greater impact were at least 30.

        Although the fire accidents of electric vehicles are on the rise, so far, there is no evidence that the risk of fire and explosion of electric vehicles is higher than that of traditional fuel vehicles. But electric cars are new, and consumers will have some doubts in their hearts. For a long time, the short cruising range and the difficulty in supporting charging facilities have been regarded as the main obstacles to the promotion of electric vehicles, but in fact, the safety issue cannot be ignored.

       Safety issue comes first, energy density comes second

        As the "heart" of electric vehicles, power batteries are the source of kinetic energy for electric vehicles and the most critical core component. Industry professionals said that among the various performances of power batteries, safety performance is the most important, which is more important than the energy density, power, number of charge and discharge, and charging time of the battery.

        From a global perspective, in order to obtain a better cruising range, battery companies and automobile companies are keen to develop higher energy density power batteries. Battery China.com learned that the goal of global power battery energy density in 2020 is basically 300wh/kg, and technology research and development at home and abroad are basically at the same level, but safety research needs to be strengthened. Domestically, under the guidance of the national new energy subsidy policy, battery companies have already sounded the clarion call for a large-scale march toward high-nickel 811 ternary batteries in order to pursue higher energy density batteries.

        Generally speaking, as a closed energy system, lithium batteries are difficult to be compatible with high energy density and safety in principle. The higher the energy density of the battery, the higher the probability of a combustion and explosion accident. According to industry insiders, the core of battery safety lies in the battery management system. Tesla claims that the energy density of battery cells can reach 300wh/kg, although Tesla has better solved the heat caused by the increase in energy density through battery system management technology. Out of control problem. But if the energy density is to be further improved, it will pose greater challenges to battery safety management.

        Yang Yusheng, an academician of the Chinese Academy of Engineering, emphasized on many occasions that continuously increasing the specific energy of batteries is a very dangerous way. He said that in order to obtain subsidies, some battery companies put energy density in the first place in product development. In order to increase the energy density, the ternary battery cathode material system is moving from 111, 523 to 622, 811 material system, by increasing the nickel content to increase the voltage, but with it, the risk of thermal runaway increases, and the battery safety risks continue. Increase. He believes that the principle of "making good use of mature and safe batteries" should be adhered to to develop safe and energy-saving electric vehicles.

        Constantly climbing new heights of energy density, while breaking the key constraint on the range of electric vehicles, it is also promoting the technological progress of the entire battery industry. However, if a higher energy density is obtained, but safety cannot be guaranteed, then the gain will not be worth the loss after all, and it may even be embarked on an evil path. Ouyang Minggao, an academician of the Chinese Academy of Sciences, said that the development safety of high specific energy power batteries for electric vehicles is always the first, followed by performance indicators such as specific energy.

        When the production process and battery management system are relatively immature, it is not appropriate to blindly emphasize energy density. Electric vehicles must ensure absolute safety, not just safety compliance. From the user's point of view, the safety of power batteries means that even if electric vehicles are charged overnight, there can be no risk; from the perspective of battery suppliers, safety requires that the energy of the battery is not triggered after being packaged in the car.

       Safeguarding the responsibility

        The battery catches fire, whether it is caused by overcharge or short circuit, most of the reasons are caused by the thermal runaway of the battery cell. Industry professionals said that at present, new materials can be selected according to the chain reaction mechanism of lithium-ion batteries to block thermal runaway chain reactions. Specific measures include the doping and coating of positive and negative electrodes, adding electrolyte flame retardant additives, and the use of polymers and solid electrolytes.

        In fact, it is not only the battery cell itself that affects the safety of electric vehicles, but also battery packs, power systems, complete vehicles, etc., especially the battery management system, and even the correct use of electric vehicles by consumers. Industry experts pointed out that the safety of electric vehicles is not a problem of a certain link or a certain enterprise, but a system project involving the entire chain of the new energy automobile industry and even the consumer side.

        The quality of power batteries affects the safety and endurance of electric vehicles. In particular, safety issues should be precautionary. Professionals in the industry said that the more attention should be paid to safety issues, especially when battery energy density continues to increase. All power battery related companies must start with safety design, from materials to structure to overall, and finally to the matching with the whole vehicle and maintenance in use, and consider and solve the safety problems of power batteries from the entire industry chain and the life cycle.

         Safety issues caused by the fire of a Weimar car must be taken seriously. As the saying goes, safety accidents are nothing minor, and safety responsibilities are heavy. To ensure the safety of electric vehicles, not only battery companies need to provide reliable battery products, but auto companies also have an inescapable responsibility. Only when the two parties cooperate in an all-round way can safety issues be minimized.