Modeling temperature distribution in cylindrical lithium ion batteries for use in electric vehicle cooling system design

Abstract

Recent advancements in lithium ion battery technology have made BEV's a more feasible alternative. However, some safety concerns still exist. While the energy density of lithium ion batteries has all but made them the premier electric vehicle (EV) battery choice, their potential to overheat and explode is a limiting factor. Beyond certain temperature thresholds, lithium ion batteries will experience what is known as thermal runaway. During thermal runaway, the temperature of the battery increases uncontrollably and fires and explosions can occur. For this reason, adequate thermal management is a necessity in bringing lithium ion battery powered vehicles to market. The purpose of this work is to 1) develop mathematical models for temperature distribution and heat transfer in cylindrical lithium-ion cells and battery packs, 2) derive the target heat transfer coefficient for an EV cooling system 3) analyze the key design parameters of EV thermal management systems, and, ultimately, 4) determine the method of cooling necessary to prevent thermal runaway. The models are based on the fundamentals of heat transfer and are integrated into computer simulations for testing. Based on the models developed in this analysis, forced convection at the surface of the battery pack is not sufficient for preventing thermal runaway outside of minimum operational requirements (low ambient temperatures and discharge rates). For typical vehicle usage, a system in which the working fluid penetrates the pack is needed. There may be potential for a hybrid cooling system: one that relies on surface convection for less strenuous operation and strategically placed cooling channels for typical and extraneous operation.