Study On Heat Generation And Aging Characteristics Of Lithium Ion Battery Based On Electrochemical Mechanism Model

New energy vehicles have broad prospects in reducing greenhouse gas emissions and environmental pollution,while lithium-ion batteries have become the first choice for electric vehicles because of their high energy density and long service life.Although lithium-ion batteries have continuously improved in terms of cost,safety,energy,and power in recent years,the thermal safety and cyclic aging and degradation characteristics they face in the working process are still factors that hinder the overall development of electric vehicles.Therefore,this article takes a nickel-rich square ternary power lithiumion battery as the research object,uses experimental testing and simulation modeling and other methods to focus on the electrochemical reaction law,heat generation mechanism and cyclic aging of the power lithium-ion battery during the working process.In-depth research and analysis have been carried out on the characteristics of decay.The main research contents and conclusions are as follows:A power battery test experimental platform was built,and experiments such as charge and discharge test,standard capacity test,accelerated cycle aging test,reference performance test,etc.were carried out.From the experimental point of view,the macro heat production and capacity attenuation of nickel-rich square ternary lithium batteries were preliminarily explored.law.The experimental test results show that the increase in discharge rate and the decrease in ambient temperature increase the heat production of the battery,and the dischargeable capacity of the battery after several cycles of charge and discharge has a significant "shrinkage" phenomenon;the capacity decline of the battery is between the number of cycles There is a non-linear relationship,and the capacity decay rate of the battery in different cycle stages is different.The decay process can be summarized into three stages,namely,rapid decay in the early stage,slow decay in the middle,and rapid decay in the later stage.The electrochemical thermal coupling model is established,and the accuracy and reliability of the coupling model are verified by the test data of charge and discharge experiments.Based on the coupling model,the law of mass transfer and diffusion inside the battery is clarified,and the internal heat generation mechanism and heating characteristics of the battery are analyzed with emphasis.Finally,the influence of key structural design parameters on the heat generation of the battery is investigated.The simulation results show that the changes in the solid and liquid lithium ion concentration in different areas of the lithium-ion battery are closely related to the changes in the electrode and electrolyte current density,and at the same time affect the internal heat generation characteristics;the heat generation rules in different areas are not the same,and the total output in the negative electrode area The heat distribution is relatively flat,the total heat production in the diaphragm area is small and can be ignored,and the total heat production in the positive electrode area is close to the total heat production in the electrode.The polarization heat generated in the negative region is much greater than the polarization heat generated in the positive region.The increase of the discharge rate makes the ohmic heat of the positive electrode area increase rapidly,and the polarization heat of the negative electrode area increases significantly;the increase of the particle size of the positive and negative electrode materials increases the total heat production of the corresponding positive and negative electrode areas,but basically does not affect the other area.Total heat production.A cyclic aging decay model considering the formation and growth of the SEI film was established,and the accuracy of the aging model was verified by the accelerated cyclic aging test data.Based on the cyclic aging decay model,the influence of environmental temperature,discharge rate,discharge cut-off voltage and other influencing factors on battery capacity are explored,and the interaction between the formation and growth of SEI film and the above influencing factors is revealed.The research results show that the increase of ambient temperature and discharge rate and the decrease of discharge cut-off voltage will accelerate the capacity decay of the battery;the growth of SEI film is limited by reaction kinetics and diffusion,and the growth rate of SEI film is faster in the early stage of cyclic charge and discharge.As the cycle progresses,the growth rate of the SEI film tends to be slow;to a certain extent,by reducing the ambient temperature and the discharge rate and increasing the discharge cut-off voltage,the growth of the SEI film can be limitedly slowed down,and the aging of the battery can be slowed down.