Experimental Study for Detection of Thermal Runaway, Explosion, and Fire in Li-Ion Batteries Initiated by Hot Plate Method
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Abstract
CORBIN COE. Experimental Study for Detection of Thermal Runaway, Explosion, and Fire in Li-Ion Batteries Initiated by Hot Plate Method(Under the direction of DR. NICOLE BRAXTAN)In 2006, Tesla announced the first fully electric lithium-ion battery (LIB) powered car, and shortly after in 2010, the Chevy Volt and Nissan Leaf began production [1]. Through the Recovery Act, the United States Department of Energy has since invested $115 million to install 18,000 residential and commercial electric vehicle (EV) charging stations across the country [1]. Industry manufacturers have also added thousands more charging locations and there will only be more in the years to come [1]. It’s clear that LIB powered vehicles are the future of human travel, with predictions from UBS Bank that 20 percent of new car sales in 2025 will be electric, and virtually 100 percent will be by 2040 [2]. Electric cars are not the only industry with emerging LIB technology, as both passenger and freight, rail manufacturers and operators are preparing to integrate the technology as well. One of the main challenges presented by this mass influx of LIB usage is their safety. Reports of LIB battery fires in vehicles started occurring shortly after they were introduced, such as the May 2011 Chevy Volt that caught fire a week after crash testing in a National Highway and Traffic Safety Administration (NHTSA) parking lot, burning multiple cars [3]. There have since been dozens of LIB fire incident reports and their numbers increase with growing production. Manufacturing defects and battery abuse are the leading causes of fire incidents [4]. Being able to predict and prevent unsafe LIB scenarios is key to their societal acceptance, economic growth, and ease of integration into everyday human life. The goal of this research was to provide insight on the effectual capacity of certain LIB characteristics on the likelihood and severity of explosions and fires when manual abuse of the cells was performed.As the common cause of LIB fire hazards, thermal runaway in the tested cells was catalyzed using hot plate-applied, thermal abuse. To measure key parameters in the LIB cells before, during, and after hot plate exposure, a unique, wireless, multi-instrument data monitoring and recording system was developed. The Fire Early Detection System (FEDS) was used to collect infrared (IR) thermal images and thermocouple (TC) temperature readings of the heated cells and their surroundings. Both single-cell, and multi-cell tests were performed to investigate the LIBs at the individual and modular level. The two most common LIB shape classifications, prismatic and cylindrical, were researched, along with three different cathode chemistries namely lithium cobalt oxide (LCO, ICR), lithium manganese oxide (LM, IMR), and lithium manganese nickel (NMC, INR). For all cells tested individually, the state of charge (SOC) of the cells was noted, to determine the effect of stored electrical energy on thermal runaway and fire. Multiple tests were performed for incrementally different SOC levels across the cells. Through analysis of the collected cell test data, key findings on the behavior of LIBs during thermal runaway were made. Selected notable findings include: • The SOC and physical structure of the cells was seen to correlate with the probability and magnitude of explosions/fires during simulated thermal abuse. • The progression of thermal runaway identifiers is consistent within all cell types, though more so in the cylindrical cells. These markers can be used to predict impending safety hazards in LIBs and could possibly be used in the prevention of some fire events. • Cylindrical cells always failed at their designed safety vents first; and any fire events successive to vent failure initiated from these vents. This information can be used to optimize safety in cylindrical module designs for both general and train-specific use. • Overall, the hot plate heating method was a reliable and controllable experiment design component. • The FEDS system was effective in conducting safe fire-data acquisition and provides a prototypical infrastructure that can continue to be improved. The contributions delivered from these findings, and the research as a whole, are as follows: • By conducting real, fire tests, independent verification of the fire initiation and propagation for LIBs was achieved, which can be used to determine the early warning stages for the FEDS. • This research has helped design a hot plate initiated, fire test setup at UNC Charlotte. This experiment design has shown that hot plate fire initiation can provide a consistent and repeatable fire start. • These tests demonstrated that, despite the different age of the batteries, they exhibit a consistent correlation between their thermal stability and fire behavior, and their SOC. • Based on this study, a fire detection and prevention strategy has been proposed.