Selective Interfacial Separation of Lithium-Ion Battery Cathodes by a Chelator-Engineered Deep Eutectic Solvent: Foil Liberation, Black-Mass Purity, and Process Windows

ABSTRACT: Direct recycling of spent lithium-ion batteries requires selective dissociation of the cathode coating on the aluminum current collectors while minimizing cross-contamination of the recovered fractions. In this study, a chelator-based deep eutectic solvent (ChelaDES) made of levulinyl hydroxamic acid, glyceric acid, and trimethyl (2-methoxyethyl) ammonium chloride was designed as a low-temperature solvent for the selective interfacial separation of LCO, LFP, and NCA cathodes. The method uses four complementary key performance indicators (KPIs) as interfacial separation performance measures: active material removal, mass removed per unit area, bare-Al exposure, and delamination severity score. LCO showed the fastest response, reaching 93.7% active-material removal and >99% bare-Al exposure at 90 °C for 60 min. NCA showed intermediate behavior, reaching approximately 92.5% removal and 82% bare-Al exposure, while LFP exhibited threshold-controlled delamination, reaching 90.8% removal but only 66% bare-Al exposure under the same conditions. Among the kinetic models tested, the PSO-Arrhenius model provided the best overall fit for process comparison, giving apparent activation energies of 25.5, 26.5, and 28.5 kJ·mol⁻¹ for LCO, NCA, and LFP, respectively. A strong correlation was observed for all chemistries between the removed mass per area and bare-Al exposure, which proves to be a useful, rapid quantitative proxy of foil liberation. Further purification studies with SEM-EDXS, XPS, and TGA/DTG suggested that the recovered black mass contained minimal impurities with minimal Al/Cu carryover (<0.1 wt%) and that the aluminum foil remained largely intact. Process heatmaps define the chemistry-specific operating windows, demonstrating that selective interfacial weakening, not bulk dissolution, controls separation. The process, therefore, acts as an upstream selective delamination and purification step, producing cleaner recovered black mass while preserving the current collector.