High-Performance LiFePO4 Regeneration through Na-Induced Lattice Activation and Conductivity Rewiring

Abstract

The recycling of spent LiFePO4 (LFP) is crucial for the sustainable development of Li-ion batteries. However, conventional lithium-replenishment repair merely restores the material to its original state, falling short of the performance required for next-generation electrodes. Herein, we propose a lattice-synergistic activation strategy that enables the upcycling of degraded LFP by simultaneously enhancing both electronic and Li+ transport pathways. Through Na doping at Li sites, the lattice of regenerated LFP is effectively activated. The larger ionic radius of Na+ expands the Li+ diffusion channels and significantly accelerates Li+ transport kinetics. Moreover, the stronger electron-cloud overlap between Na+ and O2- shifts electron density from O2- to Na+. To maintain charge neutrality, electrons migrate from Fe2+ to O2-, inducing partial oxidation of Fe2+ to Fe3+. The coexistence of Fe2+/Fe3+ lowers the electron migration barrier across Fe 3d orbitals, leading to a marked improvement in electronic conductivity. As a result, the regenerated LFP with 5% Na delivers a high discharge capacity of 141.1 mAh g-1 at 1 C with 99.4% capacity retention after 100 cycles. Even at a high rate of 5 C, it maintains 99.0% retention over 400 cycles. This Na-induced lattice-activation strategy bypasses the limitations of traditional Fe-site doping, which typically requires breaking the Fe-O bond, and opens a new avenue for both the regeneration and performance upgrading of lithium battery materials.