Multi-field Coupling Model And Cooling System Design Of Lithium Ion Battery

With the excessive use of traditional energy,energy crisis and environmental pollution become increasingly prominent,which promotes the development of new energy industry.Since 1990s,lithium-ion battery has become a promising new generation of energy storage equipment duo to its high energy density,high voltage platform,long life,friendly to the environment and so on.But at the same time,there are performance degradation and safety problems.To solve these problems,in addition to improving electrode,electrolyte,diaphragm and so on through experiments,the way of studying the internal mechanism of the battery by establishing mathematical model and giving the improvement scheme theoretically and systematically has gradually been widely used.Lithium-ion battery modeling involves many physical fields such as electrochemistry,thermology,mechanics,so it is necessary to model each physical field separately,including the change of lithium-ion concentration,potential change,temperature change,stress evolution,capacity attenuation,etc.,and then get the coupling model by considering the correlation between these variables.This model can be applied to the prediction of electrochemical,thermal and mechanical behavior,so as to explore the causes of electrochemical failure,mechanical deterioration,thermal runaway and other problems,and give improvement schemes.The main research work of this paper includes the following aspects:（1）Different from the empirical model,a universal thermal-electric-chemical-mechanical coupling analytical model of lithium-ion battery is constructed based on non-equilibrium thermodynamics.The multi-field prediction results of the model show that high-rate discharging can lead to electrochemical failure and higher temperature rise of the battery.The negative particles are subjected to compressive stress in radial direction and tensile stress in tangential direction,which increases the tendency of cracking.The model can also predict the concentration distribution,heat production change,strain distribution,displacement distribution,etc.,which provides a theoretical basis for studying the internal coupling failure of batteries.（2）The capacity fading model of lithium-ion battery is constructed by describing the local side reaction current to extend the prediction ability of thermal-electric-chemical-mechanical model on the cycle performance,and the battery selection model with multi-performance calculation is obtained by these two models.Based on the selection model,the thermal management performance,cycling performance and mechanical properties of different anode,electrolyte materials and working conditions are compared.The results show that,LFP has the best comprehensive performance,and the best electrolyte is LiPF₆dissolved in a 3:7 liquid mixture of EC and EMC.On this basis,the extreme working condition of battery is further calculated as C=11,DOD=100%.（3）The coupling effect between the velocity field of cooling medium and the temperature field of battery is studied by the thermal-electric-chemical-mechanical model,and the three-dimensional cooling model of battery is obtained.Different battery structures and cooling structures are compared.For single battery,the best cooling mode is turbo fan cooling with rotating speed of 960 rad/min,number of fans 2 and fan radius of 20 mm.For battery pack,the best cooling mode is u-shaped pipe with inlet flow rate of 1 m/s and pipe number of 4.