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Power battery safety test and standardization evaluation

Wang FANg, deputy chief engineer of the China Automotive Technology and Research Center Co., Ltd., gave a speech at the conference to discuss the safety test and standardization evaluation of power batteries.

In Wang FANg's view, to study the safety test of power batteries, we must first consider the types of accidents in the electric vehicles, and then develop corresponding test methods and projects to achieve the purpose of improving the safety of power battery products. According to the investigation, it is found that the higher proportion is charging or overcharging, then mechanical damage, spontaneous combustion, etc. In addition, there are internal short circuit, thermal runaway, etc., and finally spontaneous combustion occurs in the battery part.

Specifically, first, charging and overcharging. Most of the charging accidents that have occurred at the end of the charging period or after the charging is completed have been put on hold for a while. We have to think deeply about what causes the accidents in such a state. Second, collision. The problems caused by collisions should be classified as machinery. In addition to direct mechanical collisions, everyone is more concerned with the secondary mechanical safety brought about by the mechanical reliability of power batteries during the use of electric vehicles. The use of reliability reduces the potential for safety incidents. Third, soak the water. This is also an accident of safety caused by mechanical reliability. Fourth, the state of thermal diffusion.

Through accident analysis, it can be found that many accidents are caused by manufacturing reasons, reasons for use and reasons for monitoring. Many are a combination of various factors. First of all, some defects in the raw materials themselves and problems caused by the quality control level of manufacturing. Second, the security risks caused by the lack of technology in the system integration process. Third, in the actual use process, the first category is abuse, and the second category is the hidden danger caused by normal aging caused by dendrite growth, structural damage, etc., and accumulated to a certain extent, the explosion has led to a safety accident.

At present, Volkswagen's requirements for the long range of electric vehicles and some demands for fast charging, on the one hand, bring about rapid development of technological changes, but also bring a series of challenges: First, the challenges brought by the increase in energy density. According to the results of laboratory tests in recent years, the energy density of the system has changed significantly from 90 watt-hours/kg in 2015 to 140 watt-hours/kg now.

Second, the challenge of material system changes. In order to pursue high specific energy, it is necessary to go from lithium iron phosphate to ternary. This change also brings about changes in thermal stability and the difference between the advance of thermal runaway time and the amount of released oxygen.

Third, the challenge of long cruising range. Install as many batteries as possible in a limited space, and in this case, the battery will get bigger and bigger. In this case, the aluminum foil and copper foil of the battery should be made thin, and the diaphragm should be as thin as possible. In this case, the technology of the positive electrode, the negative electrode, the separator, and the electrolyte is a great challenge.

Fourth, the challenge of the safety of the whole life cycle, many accidents in the investigation, many accidents occurred more than 10,000 kilometers later, which proves that battery performance is a dynamic process, it is in the whole life cycle The available, controllable and out of control evaluations are the challenges we face. Under this premise, our battery evaluation technology may be a life-cycle evaluation project, including the attenuation of life and safety during the whole life cycle, and performance under different cycle times.

It can be said that under the application conditions of the vehicle, the power battery should contain multiple levels of evaluation. For example, the structure-activity relationship from material to battery closed-loop is a complex structure-activity relationship, the variation of the whole life cycle attenuation and the accurate evaluation of BMS. Evaluation of PACK reliability.

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