Selective Recovery of Lithium from Spent LiFePO4 Cathode Powder Using the [BSO3HMIm]HSO4–H2O2 System

Abstract

The recycling of spent LiFePO4 cathodes is critical for meeting the growing demand for lithium and reducing dependence on primary mining. Conventional hydrometallurgical routes are typically limited by high reagent consumption, poor selectivity, and secondary pollution, limiting their industrial and environmental sustainability. Herein, a green and highly selective lithium recovery process is developed by using the acidic ionic liquid 1-(4-sulfobutyl)–3-methylimidazolium hydrogen sulfate ([BSO3HMIm]HSO4) in combination with H2O2 as a mild oxidant. Under optimized conditions (H2O2/Li molar ratio of 2.118, leaching time of 240 min, and ionic liquid concentration of 0.05 mol/L), a lithium leaching efficiency of 97.38% was achieved with minimal iron co-dissolution (0.24%), corresponding to a high Li/Fe selectivity of 99.74%, demonstrating excellent selectivity. Kinetic analysis revealed that the leaching process conforms to the shrinking-core model and is controlled by intraparticle diffusion, with an apparent activation energy of 18.607 kJ/mol. Lithium was subsequently recovered from the leachate as Li2CO3 with a recovery efficiency of 80.45% and a purity of 95.86%. The solid residue, mainly graphite and FePO4, can be directly recycled for LiFePO4 re-synthesis, realizing a closed-loop resource cycle. This work offers an efficient, environmentally benign, and circular strategy for sustainable spent LiFePO4 battery recycling.