Interfacial-Electronegativity-Induced Near-Surface Tetrahedral Reconstruction Enables One-Step Upcycling of Spent LiFePO₄ for High-Rate and Long-Life Pouch Cells.

Abstract

Direct upcycling of spent lithium iron phosphate (S-LFP) into high-rate cathodes is highly desirable yet remains challenging. While conventional solid-state sintering can repair bulk lattice defects, it is intrinsically limited in reconstructing localized near-surface tetrahedral distortions, which critically impede 1D [010] Li⁺ diffusion under high-rate conditions. Herein, we propose a novel electronegative-heterointerface-enhanced solid-state sintering for one-step upcycling S-LFP into high-rate pouch-cell cathodes. In this approach, S-LFP nanoparticles are in situ encapsulated by highly electronegative heterointerfaces through temperature-controlled solid-state sintering, which finely modulates Fe d-band/O p-band hybridization, engineers O₁─O₂─O₃─O₃ tetrahedra, and accelerates Li⁺ near-surface migration. Consequently, regenerated LFP exhibits record-high rate capability (125.0 and 70.0 mA h g^-1 at 5 C and 30 C, respectively) and superior cycling stability (91.2% after 400 cycles at 5 C), significantly outperforming both conventional sintering paradigms and commercial counterparts by ∼100% at high rates. Moreover, regenerated Ah-level pouch cells retain 82.9% of their 1 C capacity at 5 C and deliver 88.0% capacity retention even after 1000 cycles, simultaneously achieving high power and energy densities that surpass those of commercial LFP (C-LFP) and demonstrating strong practical viability by successfully powering unmanned aerial vehicles. This work elucidates the fundamental correlation between electronegative heterointerfaces and tetrahedral framework for high-rate LFP.