Achieving Stable and Fast Ion Transport in Regenerated LiFePO₄ Via Vacancy-Mediated Upcycling

The high stability and low cost of LiFePO₄ batteries have fueled their rapid expansion, resulting in a growing volume of spent battery materials that require effective recycling. While direct regeneration restores cathode performance to the original state, the intrinsic steric hindrance and susceptibility to anti-site defect formation of one-dimensional ion transport channels restrict lithium-ion kinetics in regenerated LiFePO₄. Herein, we propose a vacancy-mediated upcycling strategy to regenerate LiFePO₄, enabling stable and fast ion transport. It uses lithium vacancy defects in degraded cathodes to facilitate simultaneous lithium replenishment and dopant diffusion into the lattice, achieving lattice repair and modulation. This leads to contracted Fe─O bonds and elongated Li─O bonds, which form fast and stable ion transport channels. Regenerated LiFePO₄ exhibits exceptional rate capability (101.9 mAh g^-1 at 10 C) and low-temperature performance (64.3 mAh g^-1 at -20°C). After 1000 cycles at 1 C, the cathode retains 95.7% capacity (137.6 mAh g^-1), and the cycled cathode also exhibits reduced anti-site defects and superior kinetics due to the lattice modulation. This vacancy-mediated upcycling strategy for improving cathode performance presents significant economic and environmental benefits, providing a sustainable pathway for advanced battery recycling.