Enhanced Green Leaching of Spent Lithium-Ion Batteries: Pyrolysis Pretreatment Combined with Eco-Friendly Citric Acid and Ascorbic Acid

The presence of polyvinyl fluoride (PVDF) between electrode particles is a potentially critical factor to reduce the leaching rate of the electrode materials in spent lithium-ion batteries (LIBs). Pyrolysis method was proposed to remove the PVDF to improve the leaching behavior. The pyrolysis characteristics of electrode materials, PVDF and pure LiCoO2 were analyzed to determine the pyrolysis temperature. The content of functional groups representing PVDF in the pyrolyzed and un-pyrolyzed electrode material was measured by XPS to evaluate the pyrolysis effect. Subsequently, eco-friendly citric acid and ascorbic acid was used to leach pyrolyzed and un-pyrolyzed electrode materials. Meanwhile, leaching behavior of pure LiCoO2 was also verified to evaluate the leaching effect of waste LiCoO2, the leaching behavior of pyrolyzed and un-pyrolyzed electrode materials was analyzed to evaluate the enhancement effect of pyrolysis. The morphology of the leaching residue was analyzed by SEM to verify the leaching effect. Results show that pyrolysis at 500 °C can fully remove PVDF and enhance the leaching rate of electrode materials. Further, citric acid and ascorbic acid can achieve efficient and green leaching of electrode materials. The leaching rate of Li and Co in un-pyrolyzed electrode materials is 58.51 % and 58.88 %, while it is 92.01 % and 90.87 % in the pyrolyzed electrode materials. The XPS analysis of pyrolyzed electrode materials and SEM analysis of the leaching residue also verified that the pyrolysis achieved full removal of PVDF.