Direct Recycling of Mixed-Oxide Cathodes: Balancing Cost, Performance and Environmental Trade-Offs

We compare solid-state relithiation (SSR), hydrothermal relithiation (Hydro), molten salt thermochemistry (MST), electrochemical (EC), and chemical (Chem) methods using harmonized techno-economic (Group I), electrochemical (Group II), and environmental/toxicological (Group III) metrics. SSR/Hydro occupies a leading position in Group I. EC combines low energy (143.0 kJ·g^-1) with higher material cost (147.7$·kg^-1) at the laboratory scale, yielding 71.9 pts, while Chem remains competitive (77.8 pts) despite elevated 201.4$·kg^-1 and moderate energy consumption of 333.7 kJ·g^-1. In Group II, MST and SSR lead (64.0 and 61.1 pts), followed by Chem, Hydro, and EC. In Group II, Chem/MST shows the best rate capability recovery, EC-cycling stability recovery, MST-capacity recovery. Group III follows the energy consumption track. The CO₂ emission declines as follows: EC < Chem < MST < Hydro < SSR, with method toxicity near moderate hazard for SSR/MST/Hydro/EC and highly reactive / highly toxic for Chem. Integrated performance for Groups I-III is close for methods with energy control in the range of 60-65 points (SSR, Hydro, MST, EC), while Chem leads (72.3 points). For Ni-rich cathodes, transferable methods should include a brief high-temperature step. EC/Chem can only be used for mild regeneration.