Multifunctional Oleylamine Enables Direct Regeneration of Spent Lithium Iron Phosphate Cathodes through Coupled Lattice and Interface Repair

Abstract

The rapid accumulation of spent lithium iron phosphate batteries has created an urgent need for sustainable and economically viable direct regeneration technologies. Direct regeneration requires restoring lithium stoichiometry, Fe valence, antisite defects, particle morphology, and surface conductivity. Herein, a multifunctional oleylamine‐assisted solvothermal strategy is introduced for coupled lattice and interface repair of spent lithium iron phosphate cathodes. Benefiting from its strongly coordinating amine groups and long hydrophobic alkyl chains, oleylamine simultaneously acts as an intrinsic reductant, defect‐repair mediator, morphology stabilizer, and carbon/nitrogen precursor. During solvothermal regeneration, oleylamine reduces Fe 3+ to Fe 2+ , repairs the degraded olivine framework, and suppresses Li‐Fe antisite disorder, while steric stabilization from its alkyl chains prevents particle coarsening and aggregation. Subsequent thermal treatment converts surface‐adsorbed oleylamine into a uniform N‐doped carbon coating, endowing the regenerated particles with improved electronic conductivity and accelerated Li + transport. Consequently, the regenerated LiFePO 4 (R‐LFP) cathode delivers a reversible discharge capacity of 155.2 mAh g −1 at 0.2 C and 93.5% capacity retention after 1000 cycles at 5 C. A 1.8 Ah R‐LFP||graphite pouch cell retains 82.6% of its capacity after 1000 cycles at 2 C. This work presents an integrated oleylamine‐assisted strategy for multi‐dimensional reconstruction of spent lithium iron phosphate cathodes, enabling high‐value battery recycling.