A modified manufacturing process for electric vehicle batteries, developed by University of Michigan engineers, could enable high ranges and fast charging in cold weather, solving problems that are turning potential EV buyers away.
"We envision this approach as something that EV battery manufacturers could adopt without major changes to existing factories," said Neil Dasgupta, U-M associate professor of mechanical engineering and materials science and engineering, and corresponding author of the study published in Joule.
"For the first time, we've shown a pathway to simultaneously achieve extreme fast charging at low temperatures, without sacrificing the energy density of the lithium-ion battery."
Lithium-ion EV batteries made this way can charge 500% faster at temperatures as low as 14 F (-10 C). The structure and coating demonstrated by the team prevented the formation of performance-hindering lithium plating on the battery's electrodes. As a result, batteries with these modifications keep 97% of their capacity even after being fast-charged 100 times at very cold temperatures.
Current EV batteries store and release power through the movement of lithium ions back and forth between electrodes via a liquid electrolyte. In cold temperatures, this movement of the ions slows, reducing both battery power as well as the charging rate.
To extend range, automakers have increased the thickness of the electrodes they use in battery cells. While that has allowed them to promise longer drives between charges, it makes some of the lithium hard to access, resulting in slower charging and less power for a given battery weight.
Previously, Dasgupta's team improved battery charging capability by creating pathways—roughly 40 microns in size—in the anode, the electrode that receives lithium ions during charging. Drilling through the graphite by blasting it with lasers enabled the lithium ions to find places to lodge faster, even deep within the electrode, ensuring more uniform charging.
This sped up room-temperature charging significantly, but cold charging was still inefficient. The team identified the problem: the chemical layer that forms on the surface of the electrode from reacting with the electrolyte. Dasgupta compares this behavior to butter: you can get a knife through it whether it's warm or cold, but it's a lot harder when it's cold. If you try to fast charge through that layer, lithium metal will build up on the anode like a traffic jam.
"That plating prevents the entire electrode from being charged, once again reducing the battery's energy capacity," Manoj Jangid, U-M senior research fellow in mechanical engineering, and co-author of the study.
The team needed to prevent that surface layer from forming. They did this by coating the battery with a glassy material made of lithium borate-carbonate, approximately 20 nanometers thick. The addition of this coating sped up cold charging significantly, and when combined with the channels, the team's test cells were 500% faster to charge in subfreezing temperatures.
"By the synergy between the 3-D architectures and artificial interface, this work can simultaneously address the trilemma of fast charging at low temperature for long-range driving," said Tae Cho, a recent Ph.D. graduate in mechanical engineering and first author of the study.
In the past two decades, EVs have become more commonplace on roadways as consumers look for better environmental options, but AAA survey results showed that the momentum is hard to maintain. From 2023 to 2024, the number of U.S. adults who would be "likely" or "very likely" to buy a new or used EV dropped from 23% to 18%.
And 63% said they would be "unlikely" or "very unlikely" to make an EV their next vehicle purchase. Part of the concerns are range drops over the winter, combined with slower charging, which was widely reported during the January 2024 cold snap.
"Charging an EV battery takes 30 to 40 minutes even for aggressive fast charging, and that time increases to over an hour in the winter. This is the pain point we want to address," Dasgupta said.
Follow-on work to develop factory-ready processes is funded by the Michigan Economic Development Corporation through the Michigan Translational Research and Commercialization (MTRAC) Advanced Transportation Innovation Hub.
The devices were built in the U-M Battery Lab and studied at the Michigan Center for Materials Characterization.
The team has applied for patent protection with the assistance of U-M Innovation Partnerships. Arbor Battery Innovations has licensed and is working to commercialize the channel technology. Dasgupta and the University of Michigan have a financial interest in Arbor Battery Innovations.
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