US university advises against fast charging of electric vehicles

China Energy Storage Network: According to foreign media reports, engineers at the University of California, Riverside said that commercial fast charging stations expose electric vehicle batteries to high-temperature, high-resistance environments that can cause batteries to crack, leak and lose stored capacity. To solve this problem, researchers have developed a method to charge batteries at lower temperatures, thereby reducing the risk of catastrophic damage and storage capacity loss.

(Image credit: University of California, Riverside)

Mihri Ozkan, professor of electrical and computer engineering, and Cengiz Ozkan, professor of mechanical engineering in the Marlan and Rosemary Bourns College of Engineering, led a team that used fast chargers installed along highways to charge Panasonic NCR 18650B cylindrical lithium-ion batteries in Tesla vehicles.

They also use a fast-charging algorithm based on the battery's internal resistance, which interferes with the flow of electrons. The battery's internal resistance changes with temperature, state of charge, battery age and other factors, and high internal resistance can cause problems during charging.

The UC Riverside battery team's charging method is an adaptive system that learns from the battery by checking the internal resistance of the battery as it charges. When the internal resistance comes into play, the charging method stops working so that the battery does not lose charging capacity.

(Image credit: University of California, Riverside)

In the first 13 charging cycles, the battery storage capacity caused by both charging technologies remained similar. Then, the fast charging technology caused the battery capacity to decay faster, and after 40 charging cycles, the battery only retained 60% of the storage capacity. However, when charging the battery using internal resistance charging, the battery still maintained more than 80% of its capacity at the 40th charging cycle.

Retaining 80% of capacity indicates that rechargeable lithium-ion batteries have reached the end of their useful life and are unusable for most applications. Batteries charged using the fast charging technique reached this state after 25 charging cycles, while batteries charged using the internal resistance charging method reached this state after 36 charging cycles.

Worse, after 60 charging cycles, the casing of batteries charged using the fast charging method will crack, exposing the electrodes and electrolyte to the air, increasing the risk of fire or explosion. High temperatures of 60 degrees Celsius/140 degrees Fahrenheit will accelerate battery damage and the risk of fire/explosion, but the internal resistance charging method will cause the battery temperature to be lower, eliminating the damage.

The researchers have applied for a patent for an adaptive internal resistance fast charging algorithm that could be licensed to battery and car manufacturers. In the meantime, the UC Riverside battery team recommends minimizing the use of commercial fast chargers, charging before the battery is depleted, and preventing overcharging.