Silicon-Assisted Direct Regeneration of Spent Lithium Iron Phosphate Cathodes via Coupled Lattice and Electronic Reactivation.

Direct regeneration can preserve the value of spent lithium iron phosphate (LFP) cathodes, but conventional relithiation and thermal repair remain limited by sluggish solid-state diffusion and incomplete reconstruction of the phosphate framework. A silicon-assisted strategy is introduced to couple olivine-lattice restoration with electronic and interfacial reactivation. Structural characterization and density functional theory calculations support preferential Si4+ incorporation at P-deficient sites, which locally expands the lattice, lowers the Li+ migration barrier from 0.67 to 0.43 eV, and narrows the band gap from 3.71 to 1.25 eV. These changes strengthen Fe-O orbital interactions and accelerate ionic and electronic transport. The regenerated material (Si-RLFP) delivers 150.5 mAh g-1 at 0.2 C, 102.5 mAh g-1 at 5 C, and 87.12% capacity retention after 500 cycles at 5 C. A preliminary process assessment estimates an energy demand of 3.347 MJ kg-1 and a net profit of $2.22 kg-1. This work identifies phosphate-framework reconstruction as a key factor in spent-LFP regeneration and provides a scalable strategy for the high-value and sustainable recycling of LFP cathodes.