A novel method for selective lithium recovery from end-of-life LiFePO4 automotive batteries via thermal treatment combined with a leaching process

As the demand for electric vehicles increases, effective solutions for recycling end-of-life lithium-ion batteries become crucial. Since lithium iron phosphate (LFP) batteries represent a significant portion of the automotive battery market, this research introduces an innovative method to produce concentrated lithium solutions by combining a calcination process with a microwave-assisted hydrometallurgical process. The initial steps involve safe collection and disassembly of discarded batteries to preserve components and minimize contamination. The cathode coils are separated and ground to a particle size smaller than 0.25 mm, concentrating 96% of the lithium compounds. Afterward, the cathode material undergoes calcination for 1 h at temperatures ranging from 300 to 900 °C in air and N₂ atmospheres. For samples treated in an oxidative atmosphere, the complete phase conversion of LiFePO₄ to Li₂Fe₃(PO₄)₃ occurs at 500 °C, whereas in an inert atmosphere, this phase change fully manifests at 700 °C. Different sulfuric acid concentrations (0.5, 1.0, and 1.5 mol/L) are subsequently used in the microwave-assisted leaching process for all the calcined and non-calcined cathodic powders. Using leaching with aqua regia as a reference for the complete leaching of metals, the best results in terms of lithium selectivity are achieved with samples calcined at 500 °C and leached with 0.5 mol/L sulfuric acid. Under these conditions, 75% of all the lithium and only 2.5% of all the iron are extracted in solution. This result demonstrates that calcination in an air atmosphere prior to a hydrometallurgical process plays a fundamental role in achieving high lithium selectivity without the need for any other additives.