CAREER: Understanding Spontaneous Internal Short Circuit Caused Thermal Runaway of Lithium-ion Batteries through In Situ Diagnosis

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Electric vehicles (EVs) are expected to account for more than half of passenger cars sold in the U.S. by 2030. However, costly battery fires have become a critical challenge for the burgeoning EV industry. What makes this challenge most concerning is that, in some cases, the batteries suddenly caught fire when the vehicles were not in use. These fires have been attributed to the internal short circuit of lithium-ion batteries, which is also a major cause of battery fires involving many other applications such as smart phones, laptops, and grid-scale energy storage. This CAREER research seeks to understand how an internal short circuit forms, evolves, and suddenly causes a thermal runaway event (and potentially a fire) in lithium-ion batteries. Insights from the research will advance the understanding of energetic failures of electrochemical energy systems and the development of safer batteries for EVs and many other applications. The integrated educational tasks include organizing a series of seminars on state-of-the-art energy storage technologies, creating an energy-storage club, developing a new course on battery basics, and mentoring undergraduate students in lithium-battery research and senior design projects. These tasks will be performed to train undergraduate students to meet the growing demand of workforce development for the booming EV industry in the Southeastern U.S. The integrated outreach activities include organizing hands-on workshops in local high schools with majority low-income and minority students focusing on battery basics and opportunities of battery-related emerging industries, creating and teaching a module on batteries in the BEST (Be an Engineering STudent) Experience summer camp program at the University of Alabama in Huntsville, and showcasing energy storage research at local STEM events. These activities will attract local K-12 students to STEM fields, preparing them for opportunities in the EV industry and other emerging battery-enabled industries.This research seeks to understand how an internal short circuit (ISC) forms, evolves, and triggers thermal runaway of lithium-ion battery cells through in situ diagnosis. The central hypothesis is that the threshold for thermal runaway due to ISC is a critical energy barrier, not a critical temperature. To test this hypothesis, the project will achieve three objectives: 1. determine the threshold of thermal runaway caused by ISC through in situ measurement of critical parameters, including ISC current, temperature, and heat generation; 2. understand the formation and evolution of ISC through in situ imaging and electrochemical characterization; and 3. understand the effects of current-guiding and self-cooling on ISC behaviors and risk of thermal runaway. The first objective will bridge the gap between conventional ex situ experiments and numerical modeling to identify and determine a reliable threshold of thermal runaway caused by ISC. The second objective will reveal the mechanisms and behaviors of ISC to advance the understanding of this highly localized and transient thermal-electrochemical-coupled phenomenon. The third objective will confirm the threshold energy and provide a basis for industrial engineers to develop future thermal runaway protection strategies and techniques. Together, the research will provide insight into ISC-caused thermal runaway of lithium-ion batteries and help ensure the safety of batteries that are critical to the success of the exponentially growing EV industry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.