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

The LiFePO 4 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 LiFePO 4 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 LiFePO 4 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 Fe 3+ to Fe 2+ , 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 LiFePO 4 batteries with varying degradation levels. The regenerated LiFePO 4 shows great electrochemical performance with a discharge capacity of 158.3 mA h g −1 at 0.5 C, 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.