Thermofluids Analysis of the Coolant Flow during Lithium-Ion Battery Operation

Thermal management of lithium ion battery packs has been accepted as one of the most critical application considerations amid the bad publicity suffered from the battery fires in the electric vehicles and airliners. Removal of the heat generated during lithium battery operation at high charge and discharge rates and rapid load changes is at paramount importance to restrain temperature rises. Forced air-cooling and liquid cooling via channels between cell pairs are frequently used in the designs of battery packs used in commercial applications.

In this study, liquid water-cooling of lithium ion battery packs is analyzed with a multiphysics computational fluid dynamics (CFD) model and a channel geometry is proposed to increase heat removal rates. The three dimensional CFD model geometry consists of two prismatic lithium polymer cells sandwiching a plate with the cooling channels grooved inside. Geometrical and electrochemical parameters of a 40 Ah commercial lithium polymer battery are used in the model. Non-isothermal electrochemical model of the lithium ion battery incorporates energy, charge and species balances in the solid and electrolyte phases with the electrochemical kinetics represented via Butler-Volmer equations. Effects of porous media on the energy, charge and species transport are taken into consideration. Electrochemical battery model is coupled with the flow model developed in the cooling channels. Non-isothermal momentum equation and the energy equation are solved in the cooling channels to account for the thermofluids phenomena.

Channel geometry is initially selected based on logarithmic mean temperature (LMTD) difference method. CFD model is developed based on the characteristic dimensions and the flowrate determined from the LMTD study. In the course of simulations shape and dimensions of the channel are further tuned to achieve a design enhancing heat transfer rates during the operation of the lithium ion battery.

Steady state simulations are carried out to investigate thermal management of the lithium ion battery during typical modes of operation. Temperature gradients and charge distribution inside the battery geometry are identified for different current densities drawn from the battery. A parametric analysis involving different discharge rates up to 8C is conducted. Temperature distribution at each discharge rate is obtained to estimate the possible locations of the spikes during the battery operation. Moreover, thermo-electrochemical behavior of the cell is studied at charging conditions. Charging rates beyond manufacturer recommended maximum of 2C are analyzed to estimate the accompanied rise of cell temperatures in the case of fast charging applications. Model results are exploited as preliminary design recommendations for a more inclusive thermal management system.