Numerical Modelling and Experimental Validation of the Thermal Behavior of Li-ion Batteries for EVs Applications

In this work, a dynamic 0-D electro-thermal model of a lithium-polymer battery for automotive applications is presented. The model predicts the battery temperature during its charging/discharging phases under different environmental and operating conditions, by considering the requested power or current, the coolant flow rate and its temperature as model inputs. The model was first validated with experimental data carried out at the test bench where only the convective heat transfer between the battery and the ambient air was considered. The accuracy of the internal heat generation model was experimentally assessed for different current discharge rates. Then, a liquid cooling system was designed on purpose, assembled, and installed on the battery at the test bench for the improvement of the model predictions in liquid convection conditions. Results show a very good predictive capability of the model both for the electrical quantities (battery voltage and state-of-charge) and for the thermal ones (battery and coolant temperature). The proposed model, validated for a single cell, was extended to a battery pack, which fulfills the power requirements of an urban vehicle and simulations for different cooling strategies were performed over a Worldwide harmonized Light vehicles Test Cycle (WLTC).