A simple green method for in-situ selective extraction of Li from spent LiFePO4 batteries by synergistic effect of deep-eutectic solvent and ozone

Efficient and clean extraction lithium (Li) from spent LiFePO 4 batteries (LIBs) still remains a challenge. In this paper, a green deep eutectic solvent (DES) based on ethylene glycol (EG) and choline chloride (CC), combined with ozone (O 3 ) from air source, realized highly selective leaching Li from LiFePO 4 in situ for the first time. The influence of experimental parameters on Li and Fe leaching efficiencies ( η Li , η Fe ) were studied by orthogonal and single-factor tests, and η Li  ≥ 92.2% while η Fe  ≤ 1.6% were obtained under the optimal conditions (6 h, 20 g/L, 8EG:1CC, 40 °C). The impurity Fe in the filtrate was completely precipitated as amorphous FePO 4 ·3H 2 O after heating (150 °C, 0.5 h), achieving a pure Li-solution. The leaching mechanism elucidated that the synergistic effect (acidification, replacement and oxidation reaction) between the DES and O 3 determined the phase transition of Li and Fe, promoting the efficient selective extraction of Li and in-situ separation of Fe (FePO 4 ). The average η Li and η Fe were separately 85.4% and 2.0% after ten cycles of the 8EG:1CC, indicative of its’ excellent reusability. Meanwhile, LiCl was recovered from the filtrate. This process avoided the use of strong acid/alkali and discharge of waste water, providing fresh perspectives on the green recovery of spent LiFePO 4 batteries.