Energy-level-guided redox mediator design for direct cathode recycling via chemical relithiation

초록

Rapid growth in electric vehicles and grid-scale energy storage has created an urgent need for lithium-ion battery recycling. Redox-mediator (RM)-assisted chemical relithiation offers a promising direct cathode recycling route under mild conditions; however, RM selection lacks well-defined screening criteria. This study establishes design principles for identifying optimal RM candidates by comparing three quinone-based RMs-benzoquinone, naphthoquinone, and anthraquinone-with increasing It-conjugation and progressively lower redox potentials across two solvents. Anthraquinone in dimethoxyethane provides the optimal balance among RM reversibility, lithium recovery, and stability. Although dimethylacetamide enhances lithium replenishment, it exacerbates solvent-derived interfacial degradation. By integrating spectroscopic, electrochemical, and surface analyses with density functional theory calculations, three screening criteria are identified: (i) a redox potential within the cathode lithiation window, (ii) an RM lowest unoccupied molecular orbital (LUMO) below that of the solvent LUMO, and (iii) an RM highest occupied molecular orbital (HOMO) near or above the solvent HOMO. These findings establish a predictive framework based on frontier-orbital alignment, enabling rational RM development for sustainable battery recycling.

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