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 has increased, effective solutions for recycling end-of-life lithium-ion batteries have become crucial. Since lithium iron phosphate (LFP) batteries represent a significant portion of the automotive battery market, this research presents 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 were separated and ground to a particle size smaller than 0.25 mm, concentrating 96% of the lithium compounds. Afterward, the cathode material was calcined for 1 h at temperatures ranging from 300°C 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 was achieved at 500°C, whereas in an inert atmosphere, this phase change fully manifested at 700°C. Different sulfuric acid concentrations (0.5, 1.0 and 1.5 mol/L) were subsequently used in the microwave-assisted leaching process for all the calcined and non-calcined cathodic powders. Considering leaching with aqua regia as a reference for the complete leaching of metals, the best results obtained in terms of lithium selectivity were obtained 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 were extracted in solution. This result reveals 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.