Hydrothermal leaching of ternary and binary lithium-ion battery cathode materials with citric acid and the kinetic study

Metal ions in ternary LIB cathode materials (LiCoO₂/LiNiO₂/LiMn₂O₄) were leached into hydrothermal water with citric acid at 60–90 °C. The leaching efficiency increased with temperature and time. Mn ion was completely leached at 60 °C for 5 min, and at 90 °C for 20 min, the leaching efficiencies of Li, Ni, and Co arrived at 81 %, 73 %, and 100 %, respectively. Hydrothermal leaching has a higher rate than the traditional method and avoids the pollutions caused by high-concentration acids and reductants like H₂O₂. To improve the Ni leaching efficiency, hydrothermal leaching of binary LIB cathode materials (LiCoO₂/LiNiO₂) with citric acid was performed at 90–120 °C. At above 100 °C for 20 min, the Ni leaching efficiency reached to 90 %. A shrinking unreacted-core model was adopted to predict reaction behavior, and the activated energy for leaching each metal was calculated. Additionally, a reasonable correlation of the rate constants of Co leaching at different pulp densities was attempted.