Unraveling Redox Mediator-Assisted Chemical Relithiation Mechanism for Direct Recycling of Spent Ni-Rich Layered Cathode Materials

The increasing demand for Li-ion batteries across various energy storage applications underscores the urgent need for environmentally friendly and efficient direct recycling strategies to address the issue of substantial cathode waste. Diverse reducing agents for Li supplements, such as quinone molecules, have been considered to homogenize the Li distribution in the cathode materials obtained after cycling; however, the detailed reaction mechanism is still unknown. Herein, the ideal electrochemical potential factor and reaction mechanism of the redox mediator 3,5-di-tert-butyl-o-benzoquinone (DTBQ) for the chemical relithiation of high-Ni-layered cathodes are elucidated. Here, 100% efficiency of DTBQ-assisted chemical relithiation is achieved by adjusting the direct immersion time of Li-deficient cathode electrodes. The reversible reaction features of the physical and chemical structures of both the regenerated cathodes and the DTBQ molecules are investigated using advanced characterization and density functional theory calculations. These findings emphasize the potential of redox-mediator-assisted chemical relithiation for realizing direct recycling processes and offer a facile and sustainable solution for battery recycling.