Irreversible Oxygen Redox Enables Lithium Extraction from Ternary Lithium-Ion Battery Cathodes in Water

Developing a low-cost and environmentally friendly method for lithium extraction is essential for the efficient recycling of spent lithium-ion battery (LIB) cathodes. Current technologies, such as solvent extraction/precipitation and electrochemical processes, rely on anion- or cation-rich extraction agents and necessitate further purification, leading to high energy consumption and waste pollution. Here, we demonstrate that applying mechanical treatment on ternary LIB cathodes enables water to extract lithium from the cathode materials under mild conditions, achieving Li extraction efficiencies of 99.4% for LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811), 98.9% for LiNi_0.9Co_0.075Al_0.025O₂ (NCA), and 97.1% for LiNi_0.9Mn_0.05Co_0.05O₂ (NMC955) at 150 °C. This process involves an irreversible oxygen redox reaction, resulting in the structural transformation to metal hydroxide species. Further experiments revealed that mechanical treatment leads to the formation of oxygen holes (O^2-δ), which are subsequently oxidized into O₂ gas through O-O dimerization during the hydrothermal process, creating oxygen vacancies. These vacant sites then act as channels for the release of surrounding Li⁺ ions, followed by the OH^- refilling process. Unlike previous methods, this work avoids the use of additional leaching reagents and produces high-quality end products, such as transition metal hydroxides and analytical-grade Li₂CO₃. Moreover, our proposed lithium extraction strategy further enables the recovered materials to be seamlessly reintegrated into the production of fresh cathode materials, providing valuable insights into the sustainable recycling of LIB cathodes.