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Waste lithium-ion batteries from cellphones, laptops and a growing number of electric vehicles are piling up, but recycling options are still largely limited to incineration or chemically dissolving the failed batteries. Current methods can create environmental problems and are difficult to economically produce on an industrial scale.
Traditional processes recycle some battery materials and rely on caustic alkalis, inorganic acids and hazardous chemicals that can introduce impurities. Extracting critical metals also requires complex separation and precipitation. However, recycling metals such as cobalt and lithium can reduce pollution, dependence on foreign sources and clogging supply chains.
Researchers at the U.S. Department of Energy’s Oak Ridge National Laboratory have perfected a method of dissolving batteries in a liquid solution to reduce the amount of hazardous chemicals used in the process. Their research was published in the journal Energy Storage Materials.
The simple, effective and environmentally friendly solution developed by ORNL researchers overcomes major obstacles encountered with previous methods.
Used batteries are soaked in a solution of organic citric acid (naturally found in citrus fruits) dissolved in ethylene glycol, an antifreeze commonly used in consumer products such as paints and cosmetics. Citric acid comes from sustainable sources and is safer to handle than inorganic acids. This environmentally friendly solution provides an extremely efficient process for separating and recycling metals in the battery’s positively charged electrode, called the cathode.
“Because the cathode contains critical materials, it is the most expensive part of any battery, accounting for more than 30 percent of its cost,” said Yaokai Bai, a member of ORNL’s battery research group. “Our approach could reduce battery costs over time.” The study was conducted at Oak Ridge National Laboratory’s battery manufacturing facility, the largest open-air battery research and development facility in the United States.
The processing technology developed there allows almost 100% of cobalt and lithium to be leached from the cathode without introducing impurities into the system. It is also capable of effectively separating metal solutions from other residues. Best of all, its secondary function is to recover over 96% of cobalt within a few hours without adding additional chemicals, which is often a complex manual process for balancing acid levels.
“This is the first time that one solution system covers the functions of leaching and processing,” said lead researcher Lu Yu. “It was interesting to find that the cobalt precipitated and settled without further disturbance. We didn’t expect this.”
Eliminating the need for additional chemicals reduces costs and avoids the generation of by-products or secondary waste. “We are excited that this recycling process developed by our scientists can pave the way for broader recycling of critical battery materials,” said Ilyas Belharouaq, corporate researcher and director of the Electrification Division at Oak Ridge National Laboratory.
Bai said the leaching properties of citric acid and ethylene glycol had been studied before, but this method used more acid and lower temperatures and was less effective.
“We were surprised at how quickly it came out of the solution,” Bai said. “With organic acids it usually takes 10 to 12 hours, but this one only took an hour.” Traditional solutions using inorganic acids are also slower because they contain water, whose boiling point limits the reaction temperature.
Further information: Lu Yu et al., Efficient separation and co-precipitation for simplified cathode recycling, Energy Storage Materials (2023). DOI: 10.1016/j.ensm.2023.103025
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