Performance Degradation Of Lithium Batteries In Electric Vehicles Under Driving Conditions

Electric vehicles need power batteries to provide energy for their driving.Lithiumbatteries are widely used in electric vehicles because of their unique performance advantages.However,in the normal running of the electric vehicle,the working current of the lithium battery is changing constantly,the rate of change is fast,the working interval is large,and the lithium battery is also subject to vibration from the road and the motor.If the lithium battery because of the discharge failure to frequent replacement,the user’s expectations for electric vehicles will be greatly reduced.Based on this,this thesis studies the performance degradation characteristics of lithium ion battery under UDC driving cycle.The influence of UDC driving cycle on the lithium battery is mainly reflected in the charge discharge rate and vibration stress.Therefore,this thesis first compares different battery charging technologies,and analyzes their charging efficiency and the influence on battery life.According to the relationship between the speed and the discharge rate of the battery,the discharge condition of the electric vehicle during the driving process is analyzed and determined.In the process of charging and discharging,the lithium ion battery charging of electric vehicle adopts constant current and constant voltage mode,and the discharge adopts the mode of working condition discharge.The charging circuit model and discharge circuit model of lithium battery are built,and simulation analysis is carried out in Matlab/Simulink.Secondly,in order to determine the vibration environment of electric vehicle in actual running process of the lithium battery,this thesis built contains lithium batteries,frame,suspension and tire of the electric vehicle vibration model,road model and motor excitation model,to determine the vibration under the action of lithium batteries by the road excitation and motor force.And the simulation in Matlab/Simulink,the vibration power density spectrum of lithium battery.Finally,a battery condition test platform including battery tester,shaking table,power amplifier and battery system is built.The battery tester takes charge and discharge control of the lithium battery to simulate the charging and discharging in the actual work,and the vibration test platform is used to simulate the vibration environment of the lithium battery in the actual running process of the electric vehicle.The performance degradation characteristics of Li ion battery were studied by cyclic charge and discharge tests under the condition test platform of lithium battery.This thesis on the basis of a large number of experiments,through the summary andanalysis of the test data,a mathematical model of driving in UDC lithium battery capacity attenuation under the condition of SOH to predict the life state of lithium battery by this model,and finally through the test has high accuracy of the capacity attenuation model,and provides a basis for the future development and application of lithium battery.