Upcycling spent lithium-ion battery cathodes into cobalt-polyphenol networks by DES dissolution and solvent-induced crystallization

The industrialization of the recycling of spent lithium-ion batteries presents promising opportunities and challenges. Herein, we developed a strategy of combining task-specific deep eutectic solvent (3,4,5-trihydroxybenzoic acid: choline chloride) dissolution and the following solvent-induced crystallization (SIC) for upcycling LiCoO2 (LCO) battery cathodes into cobalt-polyphenol networks. It has been confirmed that protic solvents (ethylene glycol, methanol, ethanol, and H2O) serve as effective inducing agents to achieve this strategy, playing a role in: (1) regulating the coordination environment of metal ions, initiating the self-assembly process with polyphenol anions and (2) provoking the precipitation of metal-polyphenol network particles (MPNPs) by altering the solubility. Comprehensive research indicated that when organic building blocks (phenolic acid, polyphenol compounds and their derivatives), Cl-, and inducing agents concurrently exist in the system, one-step conversion from LCO to MPNPs could be achieved. A tandem scheme is proposed based on the research for upcycling LCO into MPNPs, which are applied widely in separation, purification and catalysis. Experiments on ternary electrode materials demonstrated the robust generalizability of our strategy. This work provides valuable insights for the industrialization of spent LCO battery recycling and its transformation into novel materials. A strategy is proposed to induce the self-assembly process of metal ions with polyphenol in deep eutectic solvents (DESs) for the generation of metal-polyphenol network particles (MPNPs).