Direct and Low‐Temperature Regeneration of Degraded LiFePO₄ Cathodes at Ambient Conditions Using Green and Sustainable Deep Eutectic Solvent

Abstract The definite lifespan of lithium iron phosphate (LiFePO 4 , LFP) batteries necessitates the advancement of cost‐effective, nature‐friendly, and productive recycling techniques for spent LFP batteries. In this study, ethylene glycol (C 2 H 6 O 2 ), a sustainable and economical small organic molecule, is employed as a multifunctional hydrogen‐bonding donor, along with lithium chloride (LiCl), a readily accessible Li source and hydrogen‐bonding acceptor. Together, they form a novel Li‐salt deep eutectic solvent (DES) through hydrogen bonding interactions. This DES directly repairs and rejuvenates the spent cathode material (S‐LFP) at 80 °C. The Li‐salt DES not only replenishes the depleted Li in S‐LFP and reduces the adverse effects of Li–Fe antisite defects but also establishes a reducing environment that facilitates the reversion of degraded Fe(III) species in S‐LFP back to their original Fe(II) state. Consequently, the regenerated LFP exhibits remarkable electrochemical behavior, delivering an initial capacity of 155.6 mAh g −1 at 0.1 C and retaining 93% of its initial capacity after 300 cycles at 1 C. This approach can be scaled up to treat large quantities of LFP cathode material recovered from fully retired batteries, presenting a practical pathway toward large‐scale recycling of spent LFP batteries in the future.