| The primary objective of this thesis is to understand the interaction between the electrochemical and thermal behaviors of Li-ion batteries, which make excellent candidates for electric vehicle propulsion. Among different designs of Li-ion batteries, the spirally wound design provides the maximum energy and power densities by using minimum accessories. However, because of their low surface area to volume ratio, the spirally wound batteries retain more heat, posing safety problems when used in large sizes. Therefore, an electrochemical-thermal model is developed in this thesis for a spirally wound Li-ion battery, which will make a valuable tool in solving the thermal issues involved. The thermal part is a new one-dimensional energy balance developed from first-principles to describe heat-transport in spiral geometries. The one-dimensional thermal model saves a great deal of computational time and effort when compared to the existing rigorous two-dimensional model. The thermal model is then coupled to the electrochemical part, which includes charge and material balances in the electrode and electrolyte phases of the Li-ion battery. The coupled electrochemical-thermal model is used in optimizing the design of a spirally wound Li-ion battery, thereby demonstrating an application of the thermal model developed here for spiral geometries. The state-of-charge dependent reversible heat generated—a key unknown parameter in the battery chosen—is estimated by comparing the predictions of the electrochemical model with measured voltage-time and temperature-time data obtained from an 18650-type Li-ion battery. Then, keeping constant all parameters other than the spiral length of the battery and its outer temperature of operation, these parameters are optimized to produce the maximum energy density in a spirally wound Li-ion battery operating within a specified safety limit in temperature. |
