Thermal Modeling and Validation of a Lithium-Ion Battery Based on Electric Vehicle Measurements

In this contribution a multi-physical lithium-ion battery model is developed. The model, which is implemented in the programming language Modelica, focuses on the electric and thermal characteristics of the system. In order to obtain the parameters which are required to configure the model, measurements are performed directly on an electric vehicle during certain driving cycles. Further cycles are used to validate the calibrated model. Both the electric and thermal behavior of the entire battery system are modeled on cell level. The single cell instances are then electrically and thermally connected in order to create an entire battery system model. The electric model uses an electric equivalent circuit to describe the operating behavior of the battery. Thereby the open circuit voltage and three overpotentials with different time constants are considered. In the thermal model a heat capacity is used to model the ability to hold thermal energy whereas thermal conductivities are used to model the heat flow between the center and the surfaces of each cell. The calibrated electro-thermal lithium-ion battery model which is developed in this work can be integrated in an entire vehicle model in order to perform simulations on system level. The model can be used to investigate possible strategies for reducing the energy consumption of the entire vehicle.