Comprehensive 3D Thermal Modeling of Vehicle-Ready Battery Module

Thermal management of vehicle battery pack is crucial in determining the life/ageing of the battery pack, in establishing the range of the vehicle on a day to day basis and in determining the safety of the vehicle and occupants. An effective design of a thermal management system cannot be established solely through experimentation as it is time consuming and costly. Accurate computational models are required to aid in the design process. This study describes the development and validation of 3D computational model for simulating electrical and thermal characteristics of a vehicle-ready battery module. The modeling process starts with the full 3D CAD geometry of the module including the coolant channels and cold plate. As part of the study, an experimental test case was setup. This included a climate chamber for the initial soak of the module and to control ambient temperature. Coolant was pumped through channels underneath the cold plate atop which the cells sat in blocks. The cell bottom area conducted heat through a thermal interface material and through the cold plate. The effectiveness of cell bottom cooling as opposed to side cooling is demonstrated through this set up. Thermocouples were placed on various locations across the module including three placed vertically on a given cell. A severe constant discharge test of 1.5C and a fast charge test were conducted until the cutoff voltage was reached. The model was run under the same boundary conditions as the test setup. The battery cell electrical characteristics were evaluated to determine the electrical resistance and open circuit voltage of the cell. The cell resistance was derived as a function of both state of charge (SOC) and temperature of cell. The model also simulates the inter cell variation in current magnitude occurring due to the differences in cell temperatures. The thermal interface material (TIM) and the resistance offered by it to heat conduction through the cell bottom was also modeled. The model temperatures correlated to within 4% of experiment measurements on a transient basis. The correlation is demonstrated across all locations on the module and for the coolant.