Loss Model and Finite Element Analysis Thermal Model of a Production Fast Charging Battery Module

Accurate modeling of battery temperature rise during fast charging is challenging due to uncertainty around cell heat generation and the thermal characteristics of the materials and interfaces which make up the battery pack. High fidelity thermal models are critical to attaining the best battery pack design, since they enable a multitude of cooling and packaging approaches to be considered prior to building a prototype. In this study, a 3D finite element analysis (FEA) thermal model of a production fast charging battery module is created. A loss model is parameterized as input for the FEA model. A key part of the loss model is the entropic heating coefficient (EHC), which is the change of open circuit voltage with respect to temperature. The EHC is measured by waiting for the cell voltage to reach steady state at various temperatures in 5% and 10% state of charge intervals over its capacity. This is then corrected numerically by accounting for unwanted discharge or rebounds. The EHC is used to calculate reversible loss, and irreversible loss is calculated using terminal voltage measured from the cell. Thermal parameters of the pouch cell are estimated through experimental thermal gradients and comparisons to similar cells. An FEA model of the module, which utilizes edge cooling, is created based on physical measurements. The combined loss and FEA model was found to estimate peak temperature with an error of 3 °C or less for 0.5, 1, and 1.5 C charge rates and 8 °C for a multistep fast charge.