Three-Dimensional Electrochemical-Thermal Coupling Model For High Rate Lithium Ion Batteries

With the rise of new energy vehicles,the safety of power batteries has attracted much attention.In order to explore the reaction mechanism and heat generation mechanism of high-rate power battery,a three-dimensional electrochemical-thermal coupling model suitable for high-rate lithium ion battery was established based on COMSOL Multiphysics 6.0 simulation software.The electrochemical and thermal properties of a 15.4Ah laminated LiCoO₂/graphite lithium ion battery were systematically studied.Firstly,the key parameters of the model were measured.The OCV-SOC curves of LiCoO₂cathode and graphite anode was measured by two methods,the solid phase diffusion coefficients in the cathode and anode were measured by GITT and PITT methods,the entropic-heat coefficients of cathode and anode were measured by three-electrode test system,and the exchange current density was measured by Tafel curve and linear potential scanning method.These parameters ensured the accuracy and reliability of the model.In this paper,the full three-dimensional modeling is adopted,and the electrochemical model and thermal model share a geometric model.The three-dimensional heat generation power distribution of the electrochemical model is mapped to the thermal model as a heat source,and the three-dimensional temperature distribution of the thermal model output is mapped to the electrochemical model as a real-time temperature,and more reliable simulation results are obtained.The local current density distribution,lithium ion concentration distribution in the solid phases,lithium ion concentration distribution in the liquid phase,overpotential,current and potential distribution of lithium ion battery at different discharge rates were studied.Simulation results show that ohmic and electrochemical polarization overpotential are the main sources of polarization overpotential,contributing 38%and 58%to the total overpotential,respectively.The temperature of the battery at different discharge rates was simulated and verified.The surface temperature rise of the battery is13.9℃at the end of 2C discharge and 39.4℃at the end of 7C discharge.When the battery is discharged at 7C,the highest temperature point of the cell is near the tab at the initial stage of discharge,and the highest temperature point of the cell is at the cell center at the end of discharge.Through the study of heat source distribution,it is found that the cause of the uneven surface temperature distribution is mainly related to the uneven heat generation of the collector.Secondly,it is related to the uneven heat production of the positive electrode.The temperature of the battery at 2C charging decreases first and then rises.It is mainly due to the reversible heat action of the positive electrode.The temperature rise curve of battery discharge presents a"fast rise-gently fast rise"trend,which is also related to the reversible heat of battery,and is mainly the result of the reversible heat of the positive electrode.Finally,the heat generation of the battery is decomposed according to its properties and components.