Electric/Thermal Coupling Field Promotes Phonon Delocalization to Accelerate Defect-Repair Kinetics in Spent LiFePO₄

Solid-phase regeneration is widely considered as the most promising scalable approach for recycling spent LiFePO₄ (S-LFP) cathode. However, the sluggish defect-repair kinetics in traditional solid-phase routes remains mechanistically unclear, limiting the practical deployment of this technology. Here, theoretical calculations reveal that the phonon localization in defect-rich S-LFP is the essential factor responsible for the sluggish defect-repair kinetics. Localized phonons retard thermal diffusion, hindering the energy available to overcome defect repair barriers, and concurrently intensify electron-phonon coupling that suppresses the electron migration necessary for the reduction of Fe(III). Guided by this insight, we employ electric/thermal coupling field strategy to repair the S-LFP cathode. Carriers driven by the electric field transfer energy to phonons through electron-phonon scattering, which promotes energy redistribution across disparate phonon modes, collectively enhancing phonon delocalization. As a result, Li-Fe antisites (Fe_Li) were repaired within 5 s at 700°C, and the complete structural repair and lithiation are achieved within 60 s. Experimental results indicate that the regenerated cathode delivers a discharge specific capacity of 151.2 mAh g^-1 at 0.1C, and exhibits a capacity retention of 84.3% after 1100 cycles at 1 C. This theoretical breakthrough establishes a solid theoretical foundation for developing advanced S-LFP restoration technologies.