When Michigan temperatures drop, snow isn’t the only barrier to getting electrified vehicles on the road. Charging time may take much longer, which has turned potential EV owners away from the 21st century trend. But a new University of Michigan study suggests that lithium-ion EV batteries can be charged up to five times faster even in cold temperatures when manufactured with more charging channels and a coating.
“You go to the gas station, it takes on average three to four minutes to refuel the vehicle, whereas even with aggressive supercharging of an electric car, you're still talking about at least 30-40 minutes, and when it gets to winter time, those times can become even longer,” said Neil Dasgupta, U-M associate professor of mechanical engineering and materials science and engineer and co-author of the study.
Currently, lithium-ion EV batteries flow through a liquid electrolyte to produce electricity, but when temperatures plunge, lithium travels more slowly, thus releasing less energy and slower charging rates. The study found that the lithium ions move through the battery more quickly when more pathways are created in its electrodes and the battery is coated with a glass material.
“Inside of the battery you have lithium, which is the chemical that is moving from one side to the other and the speed at which that motion can occur depends on the temperature,” Dasgupta said.
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, he said. While that process speeds up room temperature charging, still, the movement was much slower in frigid temperatures.
Dasgupta compares this to a knife and butter. A knife can slice through a stick of butter regardless of temperatures, but this becomes more difficult in colder temperatures.
“What we found is that when you go to cold temperatures a bottleneck starts to arise on the surface of the graphite material inside the battery between the solid and liquid components,” he said.
The solution was to coat the surface of the graphite with a very thin film.
“This is a thin film on the order of nanometer scale -- we’re thinking more than 100 times thinner than a human hair” Dasgupta explained. “That very thin coating on the surface of the graphite allowed us to speed things up at low temperature.”
The coating on the graphite coupled with the creation of more pathways in the negative end of the terminal allows the lithium-ion battery to charge up to 500% faster at temperatures as low as 14 degrees Fahrenheit, which prevents the performance-hindering lithium plating from forming on the battery's electrodes.
“The chemicals used in the coating are readily available,” he said. “It doesn’t require any sort of non-earth abundant elements, its lithium, boron, carbon and oxygen.”
The idea is not to reinvent everything about the lithium-ion battery, Dasgupta added, but to use the technology as one part of the manufacturing process of the battery. The team is in the process of applying for patent protection for the technology.
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