Thermal Behavıor of Lıthıum-Ion Batterıes Under Normal and Abuse Operatıng Condıtıons

Abstract

This doctoral thesis investigates the electrical and thermal behaviors of Li-ion battery cells during the normal and abnormal conditions using the experimental and modeling methods. First, various standard battery tests were conducted in the study in order to define the related electrical and thermal parameters, such as specific heat, density, and open-circuit voltage. Then both galvanostatic charge and discharge experiments were conducted at various C-rates under various operating temperatures. Besides, thermal abuse tests were performed in an oven at different operating temperatures for both completely charged and discharged cells. In addition, the electrical behavior of the cell was observed at elevated ambient temperatures. Lastly, film heater experiments were conducted to investigate the thermal runaway behavior of the Li-ion cells at various SoC values under high operating temperatures.

In the modeling part, first, an axisymmetric 2-D Lumped model is developed using constant and variable internal resistance approaches to estimate the cylindrical Li-ion battery's thermal and electrical performances during various discharge rates and operating temperatures. Then, a 1-D electrochemical and 3-D thermal model was developed in order to predict the voltage and temperature variations of the Li-ion battery. Both models were developed and implemented within the framework of COMSOL. The developed model includes a large number of geometrical, electrochemical, and thermal parameters. Therefore, a comprehensive sensitivity analysis was done to obtain the optimum model input parameters. The sensitivity analysis also presented the important parameters that can significantly alter the cell’s thermal and electrical performance during the discharging processes. Lastly, four main exothermic reactions were implemented into the electrochemical model so that the total heat generation during these exothermic reactions was evaluated using the Arrhenius-type temperature-dependent equations.