Efficient Direct Recycling Strategy of Spent LiFePO4 Cathodes by Structural Defect Repair and Interface Construction.

The increasing number of retired LiFePO4 batteries urgently requires efficient and environmentally friendly recycling methods. The primary causes of LiFePO4 battery failure can be attributed to lithium loss and the formation of Fe(III) phases. Therefore, the synergistic interaction between the green reagent citric acid (CA) and urea (UR) achieves low-temperature spontaneous defect repair and the construction of an N-doped carbon layer. Specifically, CA creates a reductive atmosphere that reduces Fe(III) to the Fe(II) phase, thereby eliminating Li-Fe anti-site defects. Meanwhile, the amino group (─NH2) in UR acts as a nitrogen source, enabling N-doping modification of the carbon layer on the surface of LiFePO4 particles. The formed N-doped carbon layer effectively improves the electronic conductivity and lithium-ion migration dynamics of regenerated LiFePO4 (R-LFP). Moreover, the strengthening of Fe-O and P─O bonds further increases the overall structural stability of R-LFP, resulting in its remarkable electrochemical performance. The R-LFP electrode material delivers 163 mAh/g specific capacity during the first discharge cycle at 0.1C and retains 93.5% of its initial capacity after 500 cycles at 1C. This economical and environmentally friendly recycling strategy provides a greatly promising solution for the sustainable recovery of lithium-ion batteries (LIBs).