Engineers at the University of California (UC), Riverside, stated in a recent study that commercial fast-charging stations expose e-car batteries to high temperatures and high resistance, which can cause them to break, leak and lose their storage capacity. To prevent this from happening, the researchers have developed a method that allows charging at low temperatures without damaging the battery.
New algorithm leads to better battery life
Mihri Ozkan, a professor of electrical and computer engineering, and Cengiz Ozkan, a professor of mechanical engineering at Marlan and Rosemary Bourns College of Engineering, each used a set of discharged Panasonic NCR 18650B cylindrical lithium-ion (Tesla) batteries and charged them using an industrial fast-charging method as well as the specially developed UC Riverside Battery Team charging method. The results could not be more different.
It is worth mentioning that the specially developed charging method relies on an algorithm which, depending on the basis of the internal resistance of the battery, influences the charging process, as this can disturb the flow of electrons. The internal resistance of a battery fluctuates depending on temperature, state of charge, battery age and other factors. High internal resistance can cause problems during charging. The UC system learns from the battery by checking the internal resistance of the battery during charging. It does this by putting the charging process into a rest phase when the internal resistance exceeds a specified limit to eliminate the loss of charging capacity.
During the first 13 charging cycles, the storage capacities of the batteries remained similar for both charging techniques. After that, however, the industry's rapid charging technology led to a much faster reduction in capacity. After 40 charge cycles, the batteries retained only 60% of their storage capacity. Batteries charged with the UC charging method retained more than 80% of their capacity after the 40th cycle. Based on the assumption that batteries with 80% residual capacity are no longer used for electric cars, one can assume that they have reached the end of their service life.
44 per cent longer service life than industrial rapid charging
This as a benchmark indicates that the industry's fast charging method reaches the point after 25 charging cycles, while the battery charged with the UC Riverside Battery Team charging method reaches the point after 36 charging cycles. "Due to the increased internal resistance of the batteries, industrial rapid charging has a negative effect on the service life of lithium-ion batteries, which in turn leads to heat generation," said PhD student and co-author Tanner Zerrin.
"Loss of capacity, internal chemical and mechanical damage and the high heat for each battery are major safety concerns, especially considering that there are 7,104 lithium-ion batteries in a Tesla Model S and 4,416 in a Tesla Model 3," said Mihri Ozkan about the results of the study. Charging with internal resistance resulted in much lower temperatures and no damage to the battery. "Our alternative adaptive fast charge algorithm reduced capacity shrinkage and eliminated breaks and changes in the composition of commercial battery cells," said Cengiz Ozkan.
Source: Chemie.de - Rapid charging damages batteries of electric cars
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