Electric/Thermal Coupling Field Promotes Phonon Delocalization to Accelerate Defect‐Repair Kinetics in Spent LiFePO 4

Solid‐phase regeneration is widely considered as the most promising scalable approach for recycling spent LiFePO 4 (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.