Electric vehicles are taking off, with worldwide EV sales skyrocketing from around 1 million to more than 10 million over the past five years. Many automakers have pledged to transition to an all-electric fleet in the coming decade. But one of the biggest unresolved issues with EVs — and a significant barrier to more widespread adoption — is the risk of their batteries catching fire.
It’s not that EV batteries are especially prone to igniting — the risk is actually much lower than with a traditional combustion engine. The problem is that EV fires can be very difficult to put out, making them highly catastrophic. When an EV battery malfunctions, it can kickstart a chemical reaction, known as thermal runaway, that produces a lot of heat in a small space. Chemical fires don’t need oxygen to burn and can easily reignite, even after being doused with water.
EV development is moving quickly as automakers compete to get more and better cars on the road. While thermal runaway is a serious concern, many researchers are focusing exclusively on the conditions under which it occurs. Assistant Professor of Mechanical Engineering Lei Chen, on the other hand, is working to understand the root cause. “Our purpose is not just testing when does the runaway take place,” Chen explains. “I also want to find the reason, the origin, for the thermal runaway.”
His research recently got a boost with a $432,400 National Science Foundation grant that will be used to create a new research facility with an accelerating rate calorimeter as the centerpiece. The ARC system, which is expected to be installed this spring, has three different chambers, and can enable scientists to test batteries under a staggering range of temperatures — from -40 to 600° C (that’s -40 to 1112° F). Besides thermal runaway concerns, the ARC can also help researchers understand how low temperatures can affect battery performance.
One thing Chen already knows: a cause of thermal runaway is the formation of lithium dendrite — metal that can grow in tree-branch-like patterns along the battery. When lithium dendrite connects the anode and cathode, a short circuit occurs, sparking a fire. Chen suspects that the origin of lithium dendrite may be so-called user “overcharging” beyond the battery’s maximum capacity, commonly known as “charging abuse.” Defects like cracks or debonding within the battery that can stimulate formation of lithium dendrite may be another cause.
Getting a handle on what happens in the manufacturing process that can cause batteries to ignite later can go a long way toward improving battery safety. It can also help batteries work better, ultimately making EVs more functional, desirable and cost-effective. "I want to close the loop," Chen explains. "You have manufacturing defects and you have charging abuse and the two work together, and then the fire may happen. I’m looking at the entire story."
In a second research project funded by General Motors and the U.S. Department of Energy, Chen and his colleagues have developed a physics-based model to help predict where the manufacturing defects occur and where the dendrites might form on a battery. Using the model in manufacturing would be quicker than manual testing, reducing the cost. But to fully gauge if the model is accurate, Chen plans to use the ARC to test his findings and fine-tune the predictions.
Currently, there is only one ARC system in southeast Michigan that Chen is aware of. It is installed at General Motors and is only available to a select group of researchers there. UM-Dearborn’s ARC facility — which presents opportunities for chemists and chemical companies in addition to automotive engineers and others — will be open to researchers across campus, as well as to other universities. Research teams from UM-Ann Arbor, Wayne State, Oakland University and Kettering have already expressed interest. The lab will also offer new industry partnership opportunities, adding to the driving simulator, microscopy facility, clean room and other CECS facilities that are already open to corporate partners. “The availability of this facility will expand the list of collaborators,” says CECS Dean Ghassan Kridli. “By making it accessible to researchers in the field, we believe we can provide industry in southeast Michigan with top-notch researchers as well as top-notch equipment to use in their development work.”
In addition to Chen, UM-Dearborn faculty involved in the NSF project include:
- Associate Professor of Industrial and Manufacturing Systems Engineering Cheol Lee
- Associate Professor of Electrical and Computer Engineering Xuan (Joe) Zhou
- Associate Professor of Electrical and Computer Engineering Mengqi Wang
- Associate Professor of Mechanical Engineering Youngki Kim
- Professor of Mechanical Engineering Oleg Zikanov
- Professor of Mechanical Engineering Dewey Jung
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Story by Sarah Derouin and Kristin Palm
