An economical and closed-loop hydrometallurgical method to prepare battery-grade iron phosphate from delithiated LiFePO4 cathode scrap

The economical recovery of Fe and P poses a significant challenge in the comprehensive recovery of spent LiFePO4 batteries. A novel approach for the preparation of battery-grade FePO4.2H2O from iron phosphate residue by H3PO4 leaching and precipitation without alkali addition was proposed in this study. Under the optimized conditions of H3PO4 concentration of 6 mol L-1, liquid-solid ratio of 7.5 mL g-1, leaching temperature of 75 degrees C, and leaching time of 180 min, the leaching rates of 99.2% and 98.0% were achieved for Fe and P, respectively. During the leaching process, first dissolved Fe and P will recombine to form FePO4.2H2O, whereas the complete dissolution of FePO4.2H2O requires an increase in leaching temperature. Subsequently, 93.5% of Fe in the leaching solution can be precipitated as FePO4.2H2O at dilution ratio of 3.5, temperature of 90 degrees C, and crystallization time of 4 h. The mother liquor can be employed as a leaching agent after simple evaporation; thus, the closed-loop hydrometallurgical method avoids wastewater emissions. The LiFePO4/C cathode materials synthesized from FePO4.2H2O precursors exhibited an initial discharge capacity of 157.6 mAh g-1 at 0.1 C. After 100 cycles at 1 C, the reversible specific capacity remained 136.2 mAh g-1 with a capacity retention rate of 100%. This study presents an economical and environmental-friendly method for recycling iron phosphate residue, which is promising to address a crucial problem in the comprehensive recovery of spent LiFePO4 batteries.