Researchers develop green solution to recycle lithium-ion batteries

Researchers have developed a process that dissolves lithium-ion batteries to reduce the amount of hazardous chemicals used in the recycling process.

The environmentally-friendly solution was developed by Researchers at the Department of Energy’s (DOE) Oak Ridge National Laboratory (ORNL) and overcomes the main obstacles presented by previous recycling approaches.

Used lithium-ion batteries from cell phones, laptops and a growing number of electric vehicles are piling up, but options for recycling them remain limited mostly to burning or chemically dissolving shredded batteries. The current state-of-the-art methods can pose environmental challenges and be difficult to make economical at industrial scale.

The conventional process recovers few of the battery materials and relies on caustic, inorganic acids and hazardous chemicals that may introduce impurities. It also requires complicated separation and precipitation to recover the critical metals. However, recovering metals such as cobalt and lithium could reduce both pollution and reliance on foreign sources and choked supply chains.

The ORNL process involves soaking spent batteries in a solution of organic citric acid – which occurs naturally in citrus fruits – dissolved in ethylene glycol, an antifreeze agent commonly used in consumer products such as paint and makeup.

Citric acid comes from sustainable sources and is safer to handle than inorganic acids. Researchers said this process produced an efficient separation and recovery process for the metals from the positively charged electrode of the battery, called the cathode.

The research was conducted in ORNL’s Battery Manufacturing Facility, the United States’ largest open-access battery manufacturing research and development centre.

The recycling technique leached nearly 100 per cent of the cobalt and lithium from the cathode without introducing impurities in the system. It also enabled efficient separation of the metal solution from other residues. Importantly, it served a second function by recovering more than 96 per cent of the cobalt in a matter of hours, without the typical addition of more chemicals in what is usually a tricky process of manually balancing acid levels.

“This is the first time one solution system has covered the functions of both leaching and recovery,” said lead researcher Lu Yu. “It was exciting to find that the cobalt would precipitate and settle out without further interference. We were not expecting that.”

Eliminating the need for extra chemicals reduces costs and avoids creating by-products or secondary wastes.

“We are glad this recycling process developed by our scientists can pave the way for greater recovery of battery critical materials,” said Ilias Belharouak, corporate fellow and head of the ORNL’s electrification section.

The leaching performance of citric acid and ethylene glycol has been explored before, but that approach used more acid and a lower temperature, which proved less effective, according to Yaocai Bai, a member of the ORNL battery research team.

“We were surprised by how quickly the leaching happened in our solution,” Bai said. “With an organic acid, it usually takes 10-12 hours, but this took only one.”

Conventional solutions using inorganic acid are also slower because they include water, which has a boiling point that limits the temperature of the reaction.

The ORNL research is funded as a project of the Advanced Battery Recycling Consortium, or ReCell, a program of the Vehicle Technologies Office within DOE’s Office of Energy Efficiency and Renewable Energy.

Yu, Bai, Belharouak and researchers Rachid Essehli and Anuj Bisht contributed to the study, which used the DOE’s Center for Nanophase Materials Science at ORNL.

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