Reciprocal Ternary Molten Salts Enable the Direct Upcycling of Spent Lithium-Nickel-Manganese-Cobalt Oxide (NMC) Mixtures to Make NMC 622.

Cathode active material is the most valuable component of spent lithium-ion batteries, accounting for ≈30% of their overall value. Direct recycling of cathode materials involves recovering, regenerating, and reusing them without breaking down their chemical structure. This approach maximizes the added value of the cathode compound and reduces manufacturing costs by avoiding the need for virgin material production. However, one key challenge in scaling direct recycling from lab to industry is the requirement for highly purified cathode materials, contrasting with the low purity of black mass generated from battery shredding. No efficient separation process currently exists to isolate different lithium-nickel-manganese-cobalt oxides (NMCs) from each other. Thus, direct recycling technologies that can operate with mixtures of multiple NMC stoichiometries will be best-suited for industrial adoption. This study explores the direct recycling of NMC mixtures into NMC 622 using a "reciprocal ternary molten salts (RTMS)" system. Ionothermal relithiation and upcycling within the RTMS system successfully restore the layered structure, lithium content, and electrochemical performance of degraded NMCs, yielding results comparable to pristine NMC 622 (P-NMC 622).