The engineers at the University of California, Riverside, recently published a study that discusses the damaging effects of fast-charging on electric car batteries.
According to the team’s research, fast-charging stations subject electric car batteries to high resistance and temperatures that may cause leakage, cracks, and lower storage capacity.
The research team — led by Mihri Ozkan, an electrical and computer engineering professor, and Cengiz Ozkan, a mechanical engineering professor at the Marlan and Rosemary Bourns College of Engineering — developed a new charging method that works at lower temperatures with much lesser risk of catastrophic battery damages and lost storage capacities.
The new charging method is adaptive in nature. This means it “learns” from the battery by monitoring its internal resistance when charging. The system will stop the moment internal resistance kicks up to eliminate any loss in charging capacity.
To test both types of charging systems, the team first charged a set of discharged Panasonic NCR 18650B cylindrical lithium-ion batteries from a Tesla car, using fast-chargers located along local freeways. In this case, high internal resistance proved to be the root cause of many problems during charging.
Another set of batteries were, then, charged with a new fast-charging algorithm that’s based on the internal resistance of the battery. This method interfered with the smooth flow of electrons. Here, the battery’s internal resistance changed according to battery’s age, charge state, temperature, and other factors.
The battery storage capacity remained the same for both charging techniques during the first 13 charging cycles. After that, the standard fast-charging method started reducing the storage capacity of the battery. After completion of 40 charging cycles, the batteries were left with just 60 percent of their original storage capacity.
However, the batteries charged using the internal resistance charging method retained 80 percent of their original storage capacity after the 40th cycle.
When the lithium-ion batteries reach 80 percent capacity, they have almost reached the end of their useful life. The batteries subjected to the industry fast-charging method reached this stage after completing only 25 charging cycles. The batteries charged with the new internal resistance method lasted for 36 cycles.
“Industrial fast-charging affects the lifespan of lithium-ion batteries adversely because of the increase in the internal resistance of the batteries, which in turn results in heat generation,” explained Tanner Zerrin, the doctoral student and co-author of a related research paper.
After 60 charging cycles, it got even worse. The batteries charged using the fast-charging method cracked open, exposing the electrolyte and electrodes to air and increasing the chances of explosion or fire by a 100 times. Temperatures as high as 60 degrees Celsius accelerated both the risk and the damage.
“Capacity loss, internal chemical and mechanical damage, and the high heat for each battery are major safety concerns, each battery are major safety concerns, especially considering there are seven, 104 lithium-ion batteries in a Tesla Model S and four in a 416 in a Tesla Model 3,” said Ozkan.
The internal resistance method helped to keep temperatures low, minimizing the damage to zero.
Ozkan addws: “Our alternative adaptive fast charging algorithm reduced capacity fade and eliminated fractures and changes in composition in the commercial battery cells.”
“The proposed adaptive fast charging provides a novel perspective for the design of fast charging technology for electric vehicles with better safety performance and longer battery lifespan,” said Bo Dong, paper co-author and a doctoral student.
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