Valorization of Spent Lithium-Ion Battery Cathodes for the Production of Multimetallic Catalyst Precursors

Spent lithium-ion battery (LIB) cathodes were investigated as a multimetallic resource for catalyst precursor synthesis. Cathode material was leached under ultrasound using citric or sulfuric acid, with and without H2O2, to compare metal recovery, stability, and thermal transformation. Sulfuric acid with H2O2 achieved the highest extraction efficiencies, with 93.10% Co and 97.15% Mn, while Li extraction exceeded 95%. Maximum sulfuric concentrations were 12,822 mg L−1 Co, 4588 mg L−1 Mn, 185 mg L−1 Ni, and 659 mg L−1 Li. Initial citrate solution without H2O2 contained 25,870.90 mg L−1 Co, 15,121.95 mg L−1 Mn, 4118.14 mg L−1 Li, 965.79 mg L−1 Al, 162.74 mg L−1 Cu, and 12.69 mg L−1 Ni. Both liquors precipitated. The citrate system exhibited metal–citrate coordination, whereas the sulfuric system retained hydrated sulfate and aquo/sulfate species. After drying, the citrate precursor formed a carbon- and oxygen-rich matrix, while the sulfate precursor retained sulfur and oxygen at 400 °C. Citrate decomposition occurred at 200–400 °C, while sulfate transformation extended to approximately 612 °C. Reduction occurred at 400–900 °C for citrate and predominantly at 800–900 °C for sulfate. Both routes provide complementary precursor platforms for catalyst preparation; however, catalytic performance was not evaluated in this study and remains to be demonstrated.