Direct repair of spent LiFePO₄ via a closed-loop deep eutectic solvent process

The LiFePO₄ batteries are expected to face a significant wave of retirement in the coming years. This necessitates the establishment of a comprehensive and environmentally friendly recycling system for spent LiFePO₄ batteries. The traditional hydrometallurgical and pyrometallurgical methods involve high costs and serious pollution. This work provides a more efficient and environmentally benign alternative by repairing spent LiFePO₄ through a citric acid-LiCl deep eutectic solvent (DES). The citric acid and LiCl form a molten state through hydrogen bonding at lower temperatures, enabling the ambient-pressure repair. The LiCl acts as a Li source to replace the lost Li. The citric acid donates electrons to reduce Fe³⁺ to Fe²⁺, reducing electrostatic repulsion to facilitate Fe to return to its original lattice site, thereby eliminating Fe-Li anti-site defects and promoting the insertion of Li⁺ into the lattice. Remarkably, this method eliminates the strict requirement for Li/Fe molar ratio control, making it applicable to spent LiFePO₄ batteries with varying degradation levels. The regenerated LiFePO₄ shows great electrochemical performance with a discharge capacity of 158.3 mA h g⁻¹ at 0.5C, with a capacity retention of 82.8% after 600 cycles. Notably, the DES demonstrates recyclability and stable regeneration efficiency, while its eco-friendly nature further enhances the economic viability and industrial potential of this process.

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