Study And Application Of Li-ion Battery Safety

EVs(Electric Vehicles) is the inevitable choice of world transportation field underthe pressure of energy and environment. Among the vehicle large-capacity storagebatteries, Li-ion battery has the most potential of development due to its excellentoverall performance. However, its safety issues are restricting its widespread use, whichhave even affected the popularization of EVs. The safety performance under extremeconditions such as overcharge, short circuit, high temperature and nail test decides thebattery’s safety evaluation and it is the key issue in improving Li-ion battery safety.This paper mainly focuses on Li-ion battery’s safety issues under extreme workingconditions. The object of study is a domestic100A·h large-capacity lithium manganatebattery. The paper collected the battery’s basic working performance throughconventional tests and then carried out safety tests under extreme working conditions toknow its corresponding phenomena and key parameters changes. Under the help of datacollecting methods such as infrared thermal imaging, the paper built up Li-ion battery’sheat generation model, thermal model, thermal runaway model and grid model and thencarried out numerical simulations in multi-physical modeling software COMSOL toanalyze battery’s internal reaction mechanisms and calculate the changes in temperaturedistribution and electric characteristics under overcharge, short circuit, high temperatureand nail test conditions. The paper then discussed the influences of side reactions, thereason of thermal runaway and the thermal safety protection condition to provide furtherguidance in the future Li-ion battery’s design, producing and use. The contrastiveanalysis between test data and simulation results verified the feasibility and reliability ofthe3D electric thermal model this paper built under the four extreme conditions.The study showed that the potential safety hazard in overcharge process lies in sidereactions. In using the battery, effective actions should be taken to avoid thermalrunaway caused by relevant side reactions. External short circuit is a typical case ofbattery thermal abuse. In the external short circuit, the high current, short time andstrong thermal shock make up the safety hazard. Reasons of thermal runaway in hightemperature condition lie in the side reactions from negative electrode and electrolyte. It should be avoid that the battery is in high temperature environment above100℃,because the high temperature will gasify the organic electrolyte which will finally leadto battery’s rapid failure. In the process of nail test, the connecting between two currentcollectors from positive and negative electrodes drives the reaction.The study provided beneficial results: the thermal safety of Li-ion battery isdecided by many factors such as design, materials, structure, manufacture, use, etc.Methods like structure optimization, materials selection, manufacturing improvementand applying protective measures can reduce the risk of thermal runaway. Theimprovement of battery structure and materials can significantly increase the ability toresist overcharge and high temperature. Monitoring or protective devices can effectivelyavoid short circuit and overcharge condition. The safety performance analysis underextreme working conditions can facilitate raising design efficiency, loweringdevelopment cost and guaranteeing safety use.The analysis and modeling in the study has innovation methods in classificationanalysis on nail test internal thermal factors.