Halometallurgy: Reduction of Battery Cathode Materials under a Quasi-Inert Environment of Alkali Chloride Salts

This study introduces halometallurgy, an approach for reducing common Li-ion cathode materials in air using a eutectic mixture of chloride salts, with direct implications for processing battery black mass containing NMC, NCA, LCO, LNMO, and LMO. In-depth analysis, including in situ XRD, SEM/EDX, and TGA-DSC, reveals that reduction in the presence of NaCl-KCl proceeds via distinct halothermal and carbothermal routes. During the halothermal stage, lithium migrates from cathode particles into the chlorides, leading to the decomposition of layered or spinel structures into a solid solution of cubic oxides. Lithium migration facilitates the melting of the salts, resulting in the encapsulation of the oxide phase and the creation of quasi-inert conditions. This enables further reduction during the carbothermal stage and promotes the nucleation of metallic crystallites. Upon washing with water, lithium predominantly remains in the saline solution, termed halothermal brine, while the insoluble fraction consists of porous transition metal oxides and graphite. Depending on cathode composition, halothermal reduction is observed at 460–640 °C, while carbothermal reduction occurs above 620–650 °C. Typical black-mass impurities, including current collectors, binders, and electrolyte residues, were also examined, demonstrating relevance for real waste streams. The proposed treatment offers a pathway toward decentralized battery recycling.