Elimination of lattice strain to reconstruct ion transport channels facilitates direct regeneration of spent LiFePO₄ cathode materials

Direct regeneration is considered a sustainable solution to the issue of resource recycling and the environmental pollution caused by discarded lithium-ion batteries (LIBs). However, the direct regeneration of spent LiFePO₄ cathode materials still faces a formidable challenge that the irregular strains induced by the irreversible FePO₄ phase after several charge and discharge cycles hinder the regenerative replenishment of Li⁺. This work proposes a lattice stress modulation strategy that reduces FePO₄ phase into Fe₂P₂O₇ phase (reduction of unit cell volume from 271.7 to 122.6 ų), which releases the residual stress, paving continuous transport channels for Li⁺. In addition, the phase transformation reconstructs the FeO₆ octahedra, significantly decreasing the migration energy barrier of ions within the lattice. Ultimately, the steric effect is synergistically weakened, facilitating the replenishment of Li⁺ and the elimination of Li-Fe anti-site defects. The regenerated LiFePO₄ cathodes outperform commercial cathodes (80.2% capacity retention after 1000 cycles at 2 C). This work establishes fundamental principles for the pretreatment stage of the direct regeneration process and provides a paradigm shifting solution for sustainable LIBs recycling technology.