Green direct recycling of spent LiFePO4via electronic structure reconstruction and reinforced Fe–O d–p orbital hybridization for enhanced energy storage performance

Abstract

Direct recycling of spent LiFePO₄ (LFP) cathodes is a sustainable and energy-efficient strategy for recovering valuable materials while preserving the intrinsic olivine structure. Herein, we report a LiI-assisted regeneration approach that achieves electronic structure reconstruction and reinforced Fe–O d–p orbital hybridization, enabling simultaneous repair of structural defects and enhancement of Li⁺ transport kinetics. The reductive I⁻ ions promote Fe³⁺ → Fe²⁺ conversion and effectively eliminate Fe–Li antisite defects, while Li⁺ replenishment restores the stoichiometry of degraded LFP. Density functional theory (DFT) calculations reveal that LiI triggers a downward shift of the Fe 3d band center and an upward shift of the O 2p band center, narrowing their energy separation and strengthening Fe–O covalency. These electronic modifications reduce Li⁺ migration barriers and reconstruct continuous Li⁺ transport channels, as further validated by ab initio molecular dynamics simulations. In situ XRD measurements confirm reduced unit-cell volume fluctuations and enhanced FeO₆–PO₄ framework stability, demonstrating improved structural reversibility during cycling. Benefiting from this coupled structural–electronic reconstruction, regenerated LFP delivers 146.9 mAh g⁻¹ at 1 C and retains 97.4% capacity after 500 cycles, outperforming the spent material. This work proposes a green and low-energy direct regeneration route for cathode materials and provides important theoretical guidance for their efficient repair and regeneration.