Dissociation Mechanism on Spent Ternary Lithium-Ion Battery Cathode via Carbothermal Reduction Reaction with Biomass Components

Carbothermal reduction (CTR) using biomass as a reductant has shown great potential for recovering metal resources from spent lithium-ion battery (LIB) cathodes. However, the underlying dissociation mechanism of the cathode is poorly understood. In this study, the reduction effect of typical biomass components (i.e., cellulose and lignin) on nickel–cobalt-manganese (LiNi_0.5Co_0.2Mn_0.3O₂, NCM523) LIB cathode was investigated using thermogravimetric analysis and a fixed-bed reactor with series of characterization. The dissociation mechanism of the NCM523 cathode was investigated through a combination of thermodynamic analysis and density functional theory (DFT) calculations. Results showed that both cellulose and lignin demonstrated excellent performance during the CTR process of the NCM cathode. More than 97.7% of Li, Ni, and Co and 95.7% of Mn, primarily in the form of low-valence oxides, were dissociated after CTR processing at 550 °C with a holding time of 90–120 min. Furthermore, the reduced gases (CO, H₂, and CH₄) generated from the secondary pyrolysis of lignin enhanced the dissociation of valuable metals, leading to improved dissociation efficiency and shortened reduction time. Finally, the dissociation mechanism of the NCM cathode structure through the CTR process was proposed. This work provided fundamental data for green recycling of the LIB cathode.