<p>Lithium-ion batteries (LIBs) are the primary energy storage solution for electric vehicles due to their excellent energy efficiency, lack of memory effect, prolonged cycle life, high energy density, and enhanced power density. High-capacity nickel manganese cobalt oxide (NMC) pouch cells, increasingly used in automotive applications for their superior energy storage capabilities, are the focus of the model design presented in this study. The researchers developed a P2D electrochemical model and a three-dimensional thermal energy balance for a 37-Ah pouch cell to predict thermal behavior under various operational conditions. The model identifies and characterizes heat sources under different discharge rates and thermal boundary conditions. It also delineates the relationships between electrochemical processes and heat generation within the cell. At the onset of the discharge cycle, the cell’s temperature rises rapidly due to the elevated C-rate, which increases the rate of electrochemical reactions. After the initial temperature rises, the thermal profile stabilizes, and the peak temperature shifts from the tabs to the central regions. An investigation of thermal sources within the cell revealed that the heat of mixing and reversible heat in the positive electrode, along with reaction heat and reversible heat in the negative electrode, are the primary contributors to heat generation. This research examines the behavior of each heat source during the cell discharge process and its underlying mechanisms.</p>