Elimination of lattice strain to reconstruct ion transport channels facilitates direct regeneration of spent LiFePO4 cathode materials
Direct regeneration is a sustainable solution for recycling spent lithium-ion batteries (LIBs), yet the irregular strains induced by the irreversible FePO4 phase after cycling hinder Li+ replenishment in spent LiFePO4 cathodes. This study proposes a lattice stress modulation strategy that reduces FePO4 to Fe2P2O7, reducing unit cell volume from 271.7 to 122.6 Å3, releasing residual stress and reconstructing continuous Li+ transport channels. The phase transformation reconstructs FeO6 octahedra, lowering the migration energy barrier for ions. This synergistically weakens steric effects, facilitating Li+ replenishment and eliminating Li-Fe anti-site defects. Regenerated LiFePO4 cathodes achieve 80.2% capacity retention after 1000 cycles at 2C, outperforming commercial cathodes. The work establishes fundamental principles for the pre-treatment stage of direct regeneration and provides a paradigm-shifting solution for sustainable LIB recycling.