| Outline of Annual Research Achievements |
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.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
First, the research plan made for the last fiscal year has been well completed. The continuous hydrothermal leaching of spent NCM cathode materials with a citric acid/glycine mixture was achieved for the first time. During this process, high leaching efficiencies for Li, Co, Ni, and Mn were obtained with low/no acid corrosion. Then, a kinetic study during this hydrothermal leaching process using the shrinking unreacted core model was conducted. The reaction rates were determined and the activation energies for leaching Li, Co, Ni, and Mn were calculated.
Second, some research was started ahead of the research plan with excellent results. Metal components in the leachate obtained from commercial LCO/LNO cathode materials with citric acid were isolated in order through a series of precipitants, with high metal recovery rates and high product purities. These results will serve to pave the way for a better implementation of the research plan in the next fiscal year.
Therefore, it is regarded that the project is progressing more smoothly than initially planned.
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| Strategy for Future Research Activity |
Based on the results of the first and second fiscal years of this process, mixed organic acid of citric acid and glycine (referred to as acid X) was found to be a suitable acid leachant for achieving high leaching efficiency and resolving the problem of acid corrosion during the continuous hydrothermal leaching of spent LIB cathode materials. During a kinetic study, the reaction rates during the hydrothermal leaching with acid X were determined and the activation energies for leaching Li, Co, Ni, and Mn were calculated. Then, metal components were successfully isolated from the leachate solution obtained by the hydrothermal leaching of LCO/LMO cathode materials with citric acid.
In the third fiscal year, metal components in the leachate solution obtained from spent NCM cathode materials by hydrothermal leaching with acid X will be isolated using chemical precipitation. The parameters such as the pH values and the ratio of metal to precipitant during the precipitation steps will be optimized. Finally, the whole metal recovery process including hydrothermal leaching and separation processes will be evaluated considering the recovery rate, cost, and environmental impact.
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| Causes of Carryover |
Due to the global epidemic, attending or organizing an academic conference in a related area is very difficult. Some conferences were canceled, postponed, or changed to be held online. This greatly hinders the cooperation and communication among countries or different research fields. On the other hand, it became difficult or would take a very long time to order some parts or tools used in the experiments.
Recently, because the COVID-19 is slowly passing, the international communication and cooperation are becoming often, and the transportation and manufacturing are returning to normal. In the third fiscal year, it is expected to make better use of the left funds to complete research plan, purchase devices or consumes, conduct new exploratory research, and participate in various national and international conferences for reconnecting with the world.
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