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).