Reduction Behavior of Black Mass Recovered from NCM-based Spent Lithium-ion Batteries by CO Gas

The cathode active materials of lithium-ion batteries (LIBs) contain critical metals including Ni, Co, Mn, and Li. Since these metals are only produced in a few countries, it is necessary to recover them from spent lithium-ion batteries. The concentrated electrode materials of lithium-ion batteries are referred to as black mass (B/M), which contains a large amount of carbon used as the anode material, along with metal oxides used in the cathode. In this study, the effect of roasting temperature in an Ar+CO gas atmosphere on the reduction behavior of NCM (LiNixCoyMn1-x-yO₂)-based black mass powder and the recovery of Li was investigated. In the thermogravimetric analysis, the CO₂ concentration increased sharply from about 430 ℃ to a maximum value and then decreased, during which a weight gain due to the formation of Li₂CO₃ was also observed. Above approximately 700 ℃, the concentration of CO increased due to the reaction of CO₂ with the C in the B/M due to the Boudouard reaction. In the isothermal roasting in an Ar+CO 50 vol.% atmosphere, the weight of the sample decreased significantly above 696 ℃, and the final weight loss amount also increased with increasing temperature. Most of the significant weight loss is thought to be due to the Boudouard reaction. Li₂CO₃ was generated regardless of temperature. Above 696 ℃, most of the Ni and Co oxides were reduced to metals, and above 900 ℃, some of the MnO was also reduced and is thought to have been dissolved in the Ni-Co alloy. At temperatures above 696 ℃, where the NiO was fully reduced, the recoveries rate of lithium was approximately 90 % with no significant difference.