Selective Separation and Recovery of Li from Spent LiFePO4 Cathode Materials by Oxidation Roasting Followed by Low-Acid Pressure Leaching

Abstract

The environmental and economic benefits of recycling spent LiFePO4 batteries are becoming increasingly important. Nevertheless, the reprocessing of this type of material by conventional processes remains a challenge due to the difficulties of Li and Fe separation and low product purity. Herein, a new approach for recovering Li to separate iron and phosphorus from spent LiFePO4 cathode materials is developed. Selective separation of Li can be achieved by oxidation roasting followed by low-acid pressure leaching. During the oxidation-roasting stage, almost all the stable LiFePO4 cathode materials were first transformed into Li3Fe2(PO4)3 and Fe2O3, with the most suitable oxidation-roasting temperature determined to be 550 °C. Then, >96% of Li could be extracted using 0.5 mol·L−1 H2SO4 with an L/S ratio of 150 g·L−1 at 110 °C for 1 h; in contrast, the leaching of Fe was 0.03%. The mineral-phase composition of the leaching residues mainly includes FePO4·2H2O, Fe2O3, and C, which can be used as a raw material for preparing battery-grade FePO4. These findings demonstrate that the recycling process has the advantages of high selectivity for Li, excellent reaction kinetics, low acid consumption, and free oxidizing agent that may benefit the development of a circular economy.