Low/no-corrosion leaching of spent lithium-ion battery cathode materials in hydrothermal water using amino acid or mixed organic acids as the leachant

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Continuous hydrothermal leaching of spent LiNixCoyMn1-x-yO2 (NCM) cathode materials was successfully achieved employing a flow system and using a mixture of citric acid and glycine (10%/90%, referred to as acid X) as the leaching agent. After feeding the slurry of raw materials for 50 mins, the leaching efficiencies of Li, Co, Ni, and Mn achieved >90% and the pH value of the obtained leachate was kept at around 6.5. That was the first time to realize the continuous acid leaching of spent NCM cathode materials through a green process with high efficiency and low/no acid corrosion.A kinetic study for hydrothermal leaching of spent NCM cathode materials with acid X was conducted using a shrinking unreacted core model. Diffusion within the product layer was found to be the rate-limiting step for leaching Li, Co, Ni, and Mn. According to the determined reaction rates and Arrhenius equations, the activation energies for leaching Li, Co, Ni, and Mn were calculated.Furthermore, hydrothermal leaching of LiCoO2/LiNiO2 (LCO/LNO) cathode materials with citric acid was performed and the metal components in the obtained leachate were separated in order using a series of precipitants. Finally, the recovery rates of Ni, Co, and Li were 97.2, 96.1, and 94.1%, respectively, with the purities of Ni, Co, and Li in the corresponding precipitate being 96.3, 96.2, and 99.9%, respectively. With this success, an upgraded hydrometallurgical method, composed of hydrothermal leaching and precipitation separation steps, was officially launched for LIB recycling and is subject to further development.