Citrus solution enhances Li-ion battery recycling efficiency

Used lithium-ion batteries from mobile phones, laptops and a growing number of electric vehicles need to be recycled, but the options for doing so remain limited to mostly burning or chemically dissolving shredded batteries. The current state-of-the-art methods can pose environmental challenges and be difficult to make economical at the industrial scale. The current process recovers few of the battery’s materials and relies on caustic, inorganic acids and hazardous chemicals that may introduce impurities. Recovering metals such as cobalt and lithium could reduce pollution and reliance on foreign sources and choked supply chains.

Now, researchers at the US Department of Energy’s Oak Ridge National Laboratory have enhanced approaches that dissolve the battery in a liquid solution in order to reduce the amount of hazardous chemicals used in the process. This simple, efficient and environmentally friendly solution also overcomes the main obstacles presented by previous approaches.

The spent batter is soaked 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 like paint and makeup. Citric acid comes from sustainable sources and is much safer to handle than inorganic acids. This green solution produced an efficient separation and recovery process for the metals from the positively charged electrode of the battery, called the cathode.

Yaocai Bai, a member of the ORNL research team, said the cathode is the most expensive part of any battery, contributing more than 30% of the cost, because it contains critical materials. “Our approach could reduce the cost of batteries over time,” Bai said.

The recycling technique developed at the ORNL laboratory leached nearly 100% 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 and served a second function by recovering over 96% of the cobalt in a matter of hours, without the typical addition of more chemicals.

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

Eliminating the need for extra chemicals reduces costs and avoids creating by-products or secondary wastes. This recycling process could pave the way for greater recovery of battery-critical materials. 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 Bai. “We were surprised by how quickly the leaching happened in our solution. With an organic acid, it usually takes 10–12 hours, but this took only one,” Bai said.

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

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