Direct Restoration of Spent LiFePO4 via Lattice Defect Correction and Nitrogen-Doped Interface Engineering

Abstract The proliferation of spent lithium-ion batteries demands efficient, environmentally sustainable recycling technologies, yet regenerating spent cathode materials remains challenging. Here, we present a mild, scalable direct regeneration strategy for spent LiFePO4 (S-LFP) cathodes leveraging the synergistic effect of ethanolamine and LiNO3. Ethanolamine with moderate alkalinity and strong reducing capability gently removes surface passivation layers and amorphous impurities, selectively reducing Fe(III) to Fe(II) for lattice-stabilized valence balance. Thanks to its low steric hindrance and favorable mass-transport properties, it penetrates particle interiors and cooperates with Li+ from LiNO3 to fill Li vacancies, eliminating Li–Fe antisite defects and repairing distorted lattices. During subsequent annealing, ethanolamine acts as an in situ N source to form a uniform N-doped interfacial layer that suppresses side reactions and boosts charge-transfer kinetics. Regenerated LiFePO4 (R-LFP) achieves 106.04 mAh g–1 at 5.0 C with 100% capacity retention over 500 cycles. EverBatt-based assessments confirm its favorable economic and environmental benefits.