A Coupled Electrochemical-Thermal-Mechanical Model And Thermal Management For Lithium-ion Batteries

The oil crisis and environmental problems have accelerated the development of new energy industries,and traditional fuel vehicles have gradually been replaced by new energy vehicles.Power technology is a key factor in the development of electric vehicles,and lithium-ion batteries(LIBs)are widely used in electric vehicles due to their high-voltage platforms,high energy density,low self-discharge rate,and environmental protection.The internal reaction of lithium-ion battery is a complicated multi-physics process,including electrochemical reaction,the evolution of temperature c and stress.Therefore,it's urgent and imperative to establish a multi-physical coupling model for the application of LIBs.Temperature is the main factor affecting the normal operation of LIBs.In order to ensure that the battery is in safe,the battery pack thermal management system(BTMS)is required to control the temperature of the battery pack.The BTMS based on the electrochemical-thermal coupling model can accurately describe the temperature change of the battery pack.Therefore,the paper discusses the application of PCM,air cooling and liquid cooling in the BTMS based on the electrochemical-thermal coupling model and establishes a composite thermal management system.The main research work of this paper includes the following aspects:(1)A coupled thermal-mechanical-electrochemical model for LIBs is established,and the evolution of electrochemical,temperature and stress fields in the twodimensional spiral wound lithium-ion battery during discharge is simulated by COMSOL Multiphysics.It is found that the battery has edge effect due to the spiral structure through electrochemical analysis.Consequently,the marginal layer of the electrode reacts incompletely,which causes a waste of electrode material.The analysis of heat generation shows that the ratio of ohmic heat increases in high-rate and lowtemperature situations.Under a lower temperature,the battery shows incomplete reaction and its capacity decreases.The stress field analysis determines that the electrode exhibits compressive stress during discharge,and the electrode near the separator first shows the maximum stress.(2)Based on the coupled electrochemical-thermal model,a BTMs with PCM is established.The effects of thickness,type,thermal conductivity of PCM and ambient temperature are discussed.At the same time,the increase of the liquid velocity is better for reducing the maximum temperature and temperature difference of the battery pack.The central battery should be given a better cooling support due to heat accumulation.(3)Based on the coupled electrochemical-thermal model,the structure optimization of two-dimensional forced air cooling is carried out.The results show that the larger tilt angle ?,additional outlets and insulation layer is beneficial to improve the cooling efficiency.As for liquid cooling system,it is better to decrease the liquid temperature,choose appropriate cooling medium and add an additional copper plate.The temperature under the synthetic BTMs is 5 K lower than the original BTMs,and the maximum temperature difference of the battery pack is controlled within 3 K.