Epicatechin-mediated interfacial redox regulation for room-temperature aqueous direct regeneration of spent LiFePO4

Epicatechin is first proposed as a mild mediator for aqueous LFP regeneration. • An epicatechin-mediated controlled electron donation mechanism is revealed. • Rapid room-temperature relithiation converts FePO4 to LiFePO4 within 1.5 h. • Regenerated LFP delivers 161.9 mAh g − 1 and 94.07% retention after 1500 cycles at 10C. Aqueous direct regeneration is a promising route for repairing spent lithium iron phosphate (LiFePO 4 , LFP) cathodes, yet achieving complete relithiation requires the coupling of interfacial electron transfer, Li + reinsertion, FePO 4 /LiFePO 4 phase conversion, and defect recovery, which can become kinetically mismatched under strongly reducing conditions. Here, we develop an epicatechin-mediated aqueous relithiation strategy using a bio-derived polyphenol as a mild interfacial redox mediator. Epicatechin provides a mild interfacial redox environment through its catechol-type phenolic groups, enabling room-temperature relithiation. The aqueous step restores the LiFePO 4 phase and Fe valence states, while subsequent short-time annealing promotes Fe/Li site rearrangement, reduces the antisite defect content from 2.84 at .% to 1.17 at .%, and improves lattice homogeneity and interfacial conductivity. As a result, the regenerated LiFePO 4 delivers a discharge capacity of 161.9 mAh g −1 at 0.2C and retains 94.07% of its capacity after 1500 cycles at 10C, which is comparable to that of commercial LFP cathodes. This work provides a mild interfacial redox mediation strategy for efficient and sustainable aqueous direct regeneration of spent LFP cathodes. Download: Download high-res image (137KB) Download: Download full-size image