Ultrasound, which expectant parents know as the technology that enables them to see their babies for the first time, can be used at very low frequencies to serve an entirely different purpose. Researchers at KTH Royal Institute of Technology in Sweden report the first ultrasonic extraction of valuable metals from NMC electric car batteries – a major contribution to the battery recycling process.
The new method not only adds ultrasound to the process of extracting metal ions from damaged batteries, but also provides an alternative to the current use of harmful filtering agents – such as sulfuric acid. The payoff is a 50 percent reduction in extraction time and increased recovery of metal ions such as lithium, cobalt, manganese and nickel, says Xiong Xiao, a researcher in polymeric materials at KTH.
“The cornerstone of the future sustainable battery market will be resource-efficient metal recycling, allowing for a continuous supply of raw materials,” Xiao says. “The benefits will extend beyond the electrification of cars to countless systems based on sustainable energy storage – from mobile phones to electric grids.”
Ultrasound baths send waves of mechanical pressure at extremely high frequencies. In this case, the researchers used a frequency of 40 kHz – a tone well beyond the hearing range of humans. These waves create tiny bubbles that collapse, generate local temperatures of nearly 5,000°C, and produce highly reactive free radicals. The resulting agitation increases mass transfer in battery metals to the point that harsh chemicals are no longer necessary for metal extraction.
Instead, environmentally safe acids such as citric and acetic acid can be used, Xiao says.
As mentioned in the magazine green chemistry, this method achieved an average of 97 percent recovery of metal ions, which is a much higher amount of recovered metal ions compared to the same conditions when only mechanical agitation was used. The highest recovery rates for cobalt and nickel were achieved, reaching more than 99 percent, while lithium and manganese were recovered with an efficiency of 94 to 96 percent.
“Using ultrasound, Xiong Xiao has discovered a way to eliminate the need for commonly used chemicals, such as strong, almost uncontrollable acids,” says Richard Olson, co-author and lecturer in KTH’s Department of Polymer Materials.
The next step, Olson says, is to further optimize the ultrasound, for example, by using different levels of intensity and frequency in order to achieve faster extraction of the battery’s precious metals.
Xiao’s work is part of the PERLI (Process for Effective Recycling of Lithium-Ion Batteries) project 48228-1 funded by the Swedish Energy Agency. The research was conducted in collaboration with battery manufacturer Northvolt.
Advanced research makes battery recycling more economical
Xiong Xiao et al, Ultrasound-assisted extraction of minerals from lithium-ion batteries using natural organic acids, green chemistry (2021). DOI: 10.1039 / D1GC02693C
Provided by KTH . Royal Institute of Technology
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