Study On The Thermal Effect And Propagation Characteristics Of Li-ion Battery

Due to the constraints of energy shortage and environmental problems,the development of new energy vehicles has become an important trend of transportation energy transformation.The thermal safety of the lithium ion power battery has an important influence on the battery system and the safety performance,life and efficiency of the whole electric vehicle.In this paper,the characteristics of the thermal effect of the battery and the thermal propagation characteristics under the normal and thermal runaway conditions of the lithium ion cylindrical cell are analyzed.The main contents of this paper are as follows:The basic performance of the lithium battery monomer is evaluated through the experiment.The battery capacity changes under different charging and discharging rates and different ambient temperatures are analyzed and compared.Results at-20 ℃,the battery capacity decreased by 29.9%.The larger the discharge rate of lithium ion battery,the smaller the discharge capacity and the discharge platform.The discharge capacity and discharge platform of lithium ion battery are negatively correlated with discharge rate.On the basis of the electrochemical model,the heat release characteristics of the battery are analyzed,and the thermal runaway model of the battery is established by combining the heat released by the materials of each part of the battery.The analysis results can be divided into several stages for thermal runaway.The first stage: the temperature is rising linearly.This stage is mainly caused by needling,resulting in short circuit and large amount of heat released from the battery,which makes the temperature rise.The second stage: the temperature rises exponentially.This stage is due to the temperature at the moment that has reached the temperature threshold of the secondary reaction of the battery material,which makes the material of each part of the battery decompose and release a large amount of heat,which makes the temperature rise.The third stage: the temperature stable zone.This stage is finished by the material of the battery has been reacted,and it is not releasing the heat.For a number of cylindrical battery modules,the propagation characteristics of heat in different configurations of modules are studied.It is found that there is an inverse proportion between the discharge time and the discharge rate on a certain isothermal line.When the battery is in real working condition,it can provide a time early warning plan based on this characteristic to prevent high temperature and damage or even explosion to batteries.Using the Socket structure and increasing the battery gap can slow down the heat transmission rate of the battery and delay the runaway time.According to the temperature and temperature rise rate as the standard basis of different stages,we can provide a theoretical basis for the design of the battery module for thermal runaway early warning.