Heat transfer analysis through hybrid FRP composite for self-sensing lithium-ion battery enclosure

Abstract

The automotive industry is rapidly transforming due to the growing demand for decarbonization. Electric Vehicles (EVs) are becoming increasingly common, and subsequent innovations regarding vehicle lightweighting can increase vehicle efficiency and further reduce carbon footprint. Lithium-Ion Batteries (LIBs) have become the most common power source used in EVs, but LIBs host some inherent challenges, namely thermal runaway. Thermal runaway can be caused by various mechanisms including thermal, mechanical, or electrical impacts which occur during extreme operating conditions. This kind of failure can result in battery fires and explosions that are extremely difficult to extinguish and pose a significant safety risk. A self-sensing LIB enclosure that monitors the temperatures of individual battery modules and provides an early warning signal may be a viable solution to the thermal runaway safety issue. This work studies a hybrid carbon and glass Fiber Reinforced Polymer (FRP) composite designed to replace the traditional metal LIB enclosure, lightweighting the EV design and allowing for condition monitoring sensors to be embedded during the manufacturing process. Battery enclosures have tight space constraints which prohibit surface mounted sensors, making sensor embedment essential. Embedded sensors also have the advantage of a protective composite layer that makes the sensor system more robust during manufacturing and operating conditions. However, this composite layer under which the sensors are sealed produces a time lag in detecting a temperature change within the battery enclosure. This time delay would reduce the efficacy of an early warning system. The purpose of this study is to lay the groundwork for a self-sensing condition monitoring LIB enclosure and characterize the composite enclosure's temperature response at different layers. A theoretical design of said system is detailed, and a prototype enclosure sample instrumented with temperature sensors is fabricated. Experiments are performed to measure the temperature response of the self-sensing composite prototype when exposed to realistic thermal runaway conditions. This is accomplished through a novel experimental test set up that imposes a unidirectional heat transfer condition by exposing the composite sample to oven temperatures on the top surface and ambient temperatures on the bottom surface. A computational model is developed to predict the composite's thermal response during different LIB failure temperatures. This finite element transient heat transfer simulation is tuned using initial experimental results and validated by subsequent thermal tests. This study produces a high accuracy thermal model which can be used to provide design optimization information, like the ideal placement of sensors, and predict the thermal response of a composite enclosure when exposed to different thermal loading conditions. The thermal simulation could also be utilized in future works to develop a temperature inference model which could predict LIB health from em...