Balancing Leaching and Relithiation in Deep Eutectic Solvents for Sustainable LiFePO ₄ Regeneration

ABSTRACT The rapid adoption of LiFePO 4 (LFP) batteries urgently calls for economically and environmentally sustainable recycling processes. While green and low‐cost lithium‐based deep eutectic solvents (DESs) have recently been employed for spent LFP regeneration, the underlying mechanism remains poorly understood. In this work, we report for the first time the leaching phenomenon intrinsically accompanying DES‐based regeneration and propose the “Leaching‐Relithiation” synergistic‐competitive (LRSC) mechanism. Within this framework, moderate proton‐induced lattice leaching promotes relithiation, whereas excessive leaching disrupts the stoichiometry, leading to by‐product formation and inferior relithiation. In a classic Urea‐LiCl DES system, we demonstrate that controlled leaching is essential for effective relithiation under mild conditions. By simply regulating the reaction time, an optimal balance between leaching and relithiation is achieved, enabling the successful regeneration of lithium‐deficient LFP within 1 h. The regenerated LFP delivers 150.1 mAh/g at 0.1C and retains 83.4% of original capacity after 500 cycles at 1C. This process is readily scalable to large quantities of LFP cathode materials, and the DES medium can be recovered and reused. Preliminary techno‐economic analysis indicates favorable cost and energy performance relative to conventional recycling routes. The LRSC mechanism proposed in this work offers fresh insights to guide future regeneration strategies.