In a paper published in the journal Separation and Purification Technology, the researchers explain that the new method starts with pulverizing the contents of spent lithium-ion cells in a fume cupboard. The result is a finely ground black powder dissolved in a transparent liquid – oxalic acid. Both of these elements are produced in something reminiscent of a kitchen mixer.
By fine-tuning temperature, concentration and time, the researchers have come up with a remarkable new recipe for using oxalic acid.
“We need alternatives to inorganic chemicals. One of the biggest bottlenecks in today’s processes is removing residual materials like aluminum. This is an innovative method that can offer the recycling industry new alternatives and help solve problems that hinder development,” head researcher Martina Petranikova said in a media statement.
This aqueous-based recycling method is called hydrometallurgy. In traditional hydrometallurgy, all the metals in an EV battery cell are dissolved in an inorganic acid. Then, “impurities” such as aluminum and copper are removed. Lastly, valuable metals such as cobalt, nickel, manganese and lithium can be recovered separately. Even though the amount of residual aluminum and copper is small, it requires several purification steps and each step can cause lithium loss.
With the new method, the researchers reverse the order and recover the lithium and aluminum first. Thus, they can reduce the waste of valuable metals needed to make new batteries.
The latter part of the process, in which the black mixture is filtered, is reminiscent of brewing coffee. While aluminum and lithium end up in the liquid, the other metals are left in the “solids.” The following phase is to separate aluminum and lithium.
“Since the metals have very different properties, we don’t think it’ll be hard to separate them. Our method is a promising new route for battery recycling – a route that definitely warrants further exploration,” Léa Rouquette, lead author of the paper, said.
“As the method can be scaled up, we hope it can be used in industry in future years,” Petranikova added.
Petranikova’s group has spent many years conducting research in the recycling of metals found in lithium-ion batteries. The group is involved in various collaborations with companies and is a partner in the Volvo Cars’ and Northvolt’s Nybat project.