Study On Aging Of Lithium Ion Battery Based On Electrochemical-thermal-side Reaction Coupling Model

Lithium-ion batteries have become the main source of power for modern electric vehicles with their outstanding performance advantages.However,the aging problem of lithium-ion batteries has restricted the development and promotion of electric vehicles,because the aging of lithium-ion batteries can affect battery performance and even internal structure,and there are many factors affecting the aging,and the situation is complicated,and the research is difficult.Therefore,it is necessary to understand the main aging mechanism and aging behavior of lithium-ion batteries,and study the influence of external factors on battery aging.Battery aging is mainly caused by the corresponding aging mechanism triggered by the battery under different operating conditions,resulting in battery performance degradation.In this paper,the combination of experiment and simulation is used to study the effect of temperature on the aging of lithium ion batteries.Firstly,the lithiumion battery was subjected to charge and discharge cycle experiments to obtain t he battery characteristic parameters.Secondly,the SEI membrane side reaction and the lithium side reaction were analyzed stepwise,and the electrochemical-thermal-side reaction coupling model of the lithium ion battery was established.Finally,Verify the accuracy of the coupled model and simulate the aging of lithium-ion batteries at different ambient temperatures.(1)Design a reasonable aging experimental program combined with environmental temperature and discharge rate that are two factors affecting battery aging.Through experimental research,we analyzed the differences of battery discharge rate characteristics,battery surface temperature rises characteristics and battery relative capacity fade trend and characteristics,and concluded the battery relative capacity attenuation curve can be roughly divided into three stages,including the initial fast decay phase,the stationary cycle phase,and the battery damage phase.(2)Simplify the battery structure and establish an electrochemical-thermal coupling model for lithium-ion batteries.Based on the same conditions as the experimental design,the rate characteristics of the simulated battery and the temperature rise of the battery surface were simulated based on this model.The accuracy of the electrochemical-thermal coupling model is verified by comparison with experimental results,which lays a foundation for the follow-up work.(3)Combined with the SEI growth model,a coupled model of electrochemical-thermal-SEI growth for lithium ion battery was established.By comparing with the experimental results,it is verified that the model can effectively simulate the prometaphase of the battery relative capacity fade trend,but cannot explain the end of the battery relative capacity fade trend.This is due to other aging mechanism occurred at the end of the battery relative capacity fade trend.Finally,the simulation analysis of the relative capacity fade of the battery at different ambient temperatures shows that the higher the ambient temperature,the higher the lithium-ion battery capacity fades in the prometaphase of the relative capacity decay of the battery,because the temperature rise accelerates the rate of SEI growth which results in an increase in the thickness and volume fraction of the SEI film,consumes more active lithium ions and lowers the battery capacity.(4)Considering that the lithium plating side reaction may occur at the end of the relative capacity decay of the battery,a coupled model of the electrochemical-thermalside reaction(including the SEI growth and lithium plating side reaction)of the lithium ion battery is established.By comparing with the experimental results,it is verified that the model can effectively simulate the whole process of battery relative capacity fade trend.Finally,the simulation of the fade of the relative capacity of the battery at different ambient temperatures shows that in the high temperature environment,the lithium plating side reaction occurs after the battery is recycled,which is the main reason for the rapid decay of the capacity of the lithium ion battery in the later cycle.