张小青

Abstract： With the support of national policies， electric vehicles have developed rapidly， but with the rapid development， some problems have gradually emerged. The frequent burning incidents of electric vehicles have cast a shadow on consumers’ hearts， and consumers have changed from paying attention to the battery life to paying attention to the safety of electric vehicles. How to use scientific and technological means to monitor and manage power batteries and realize the healthy development of new energy vehicles has become a top priority.

Keywords： thermal runaway;Battery management system; Safety management.

1 Overview of the development of electric vehicles

At present， the new energy automobile industry is welcoming subversive changes in the industry. On the one hand， emerging technologies such as artificial intelligence， big data， cloud computing and mobile Internet are deeply integrated with automobiles to create intelligent， networked and electrified electric vehicles.， sharing and mobile travel services; On the other hand， the decline of the state subsidy policy and the continuous improvement of consumer demand have forced the automobile to speed up the reform in manufacturing methods， industrial costs， etc.， and the improvement of the specific energy of the battery has been placed in the first place， resulting in some automobile enterprises ignoring the safety of electric vehicles. Safety is the lifeline of the development of new energy vehicles， the key factor in the competition of electric vehicles market， and the highlight of the core technology that can best reflect the strength of new energy vehicles.

2 Building an effective strategy for the safety management system of new energy vehicles

The charging and discharging process of the battery is actually the process of chemical reaction of electrode materials inside the battery core. When the heat emitted by the battery core plus the heat of self-reaction is less than the heat generated inside the battery core， the internal temperature of the battery core will rise， and a series of chain side reactions will be induced when the temperature of the battery reaches a certain temperature. Such as decomposition of electrolyte， dissolution of solid electrolyte interface film， dissolution of active substances， phase change of cathode material， reaction between binder and highly active cathode， and deposition of lithium metal， etc.， these chain reactions will release heat， resulting in rapid temperature rise.

Affected by electrode materials and processes， the capacity of batteries in the same batch has certain discreteness in the manufacturing process. At the same time， due to the difference in internal resistance and self-discharge rate， the capacity of power batteries is lower than before. At this time， there is inconsistency between batteries， and the working state of battery modules is determined by the worst battery cells. The sensitivity of power batteries to thermal disturbances increases after multiple charge and discharge cycles. Due to the inconsistency of single batteries， Therefore， an equalization circuit is arranged between each battery of the battery pack to implement equalization control， so that the charging and discharging working conditions of each single battery are as consistent as possible， thereby improving the safety performance of the whole battery pack and the whole vehicle.

The battery management system can monitor and manage the power battery in real time. By collecting and controlling parameters such as voltage， current， temperature and SOC （state of charge）， it can monitor， protect， balance， alarm， communicate， control and calculate the power battery， thus realizing the protection of the power battery and improving the comprehensive performance of the battery. Large-capacity lithium batteries， such as ternary batteries， have obvious inconsistencies， which will affect the charging and discharging capacity and cycle life of batteries. Battery management systems can improve inconsistencies through balancing. The best working temperature of lithium-ion batteries is 20- 45℃. The battery management system can also control the working environment temperature of batteries. It can be said that a good battery management system has a certain level of intelligence.

3 Conclusion

We should treat the frequent fire and burning incidents of electric vehicles correctly. After investigation， the main reasons for the fires of many electric vehicles are product quality problems， failure to comply with technical specifications and standards， and short technical verification period. Secondly， the state subsidy policy should conform to the law of technological development， and the improvement of energy density should not be too fast or changed too frequently. The later the battery industry develops， battery safety will become a bottleneck technology. It can be said that safety is the lifeline of sustainable development of electric vehicles. All power battery R&D departments and vehicle enterprises should take safety as the core. In a word， we should strive to solve the problem of power battery safety and ensure the healthy development of the new energy automobile industry.

References

[1]Fang Kai. Safety analysis and development suggestions of new energy vehicles [J]. Automotive Practical Technology， 2020.

[2]Tan Xiaojun. Design of Power Battery Management System for Electric Vehicle [M]. Guangzhou： Sun Yat-sen University Press， 2011.

山東工业职业学院