Chemical Transformations in Li-Ion Battery Electrode Materials by Carbothermic Reduction

The effects of pyrolysis on the composition of the battery cell materials as a function of treatment time and temperature were investigated. Waste of Li-ion batteries was pyrolyzed in a nitrogen atmosphere at 400, 500, 600, and 700 °C for 30, 60, and 90 min. Thermodynamic calculations for the carbothermic reduction of active materials LiCoO2, LiMn2O4, and LiNiO2 by graphite and gas products were performed and compared to the experimental data. Ni, Mn, and Co (NMC) cathode materials recovered from spent Li-ion batteries were also studied. The results indicate that the organic compounds and the graphite are oxidized by oxygen from the active material and provide the reductive atmosphere. Such removal of the organic components increases the purity of the metal bearing material. Reactions with C and CO(g) led to a reduction of metal oxides with Co, CoO, Ni, NiO, Mn, Mn3O4, Li2O, and Li2CO3 as the main products. The reduction reactions transformed the metal compounds in the untreated LiB black mass to more soluble chemical forms. It was concluded that the pyrolysis can be used as an effective tool for the battery waste pretreatment to increase the efficiency of the leaching in hydrometallurgical processing of the black mass. The results obtained can help to optimize the parameters in the industrial processing already used for Li-ion battery recycling, especially if followed by hydrometallurgical treatment. Such optimization will decrease the energy demand and increase the metal recovery rate and utilization of the byproducts.