Organic Acid‐Based Hydrothermal Leaching of LiFePO₄ Cathode Materials

Abstract This study conducts hydrothermal leaching of commercial LiFePO₄ (LFPO) cathode materials with oxalic acid, citric acid, or glycine without any other oxidants or reductants. Of these acids, glycine exhibits the weakest leaching behavior, with the leaching efficiency of lithium (Li), iron (Fe), or phosphorus (P) less than 15% even at 200 °C and an acid concentration of 0.8 mol L⁻¹ for 10 min. For oxalic acid, at 200 °C for 10 min, with a pulp density of 30 g L⁻¹ and an acid concentration of 0.8 mol L⁻¹, the leaching efficiencies for Li and P are 100% and 97%, respectively, and 98.5% of Fe precipitates as iron oxalate (FeC₂O₄) that can be used as a precursor for preparing LFPO cathode materials. Citric acid shows the highest leaching efficiency for Li, Fe, and P, reaching 96%, 100%, and 88%, respectively, at 90 °C for 10 min with a pulp density of 10 g L⁻¹ and an acid concentration of 0.8 mol L⁻¹. The continuous hydrothermal leaching of LFPO cathode materials with citric acid is first achieved. These results clarify the superiority of citric acid over oxalic acid and glycine with respect to the leaching efficiency for Li, Fe, and P from LFPO batteries under hydrothermal conditions.