Regenerating spent LiFePO₄ with tailored molecular groups: from bulk lattice repair to surface conductive coating for...

Due to its economic and environmental value, the recycling of spent LiFePO₄ (S-LFP) has been the subject of plenty of attention. However, it still suffers from inferior energy-storage properties, ascribed to the fact that the fading traits from bulk-phase to surface layers are hardly tailored at the same time. Herein, through the control of the active structure of amino acid, S-LFP is successfully regenerated with optimized Li-Fe anti-sites and high-conductive N-doped double carbon layers. Their internal lattice stress is effectively alleviated, bringing about the removal of phase cracks. Through the balancing between H⁺ and electrons cloud of O-atoms, the further dissolution of Fe-ions is inhibited from nano-size solid-solution LiFePO₄/FePO₄, meanwhile without the formation of by-product Li₃PO₄. The optimized capacity could be maintained at 134 mAh g^-1 at 1.0C after 500 cycles, with a capacity retention ratio 95.7%. Even at 5.0C, their initial capacity was still kept about ∼120 mAh g^-1 with a capacity retention ratio of 92.2% after 1000 cycles. Supported by the detailed kinetic analysis, the suitable anti-sites and double carbon-layers served important roles for the enhancements of ion-diffusion behaviors and the decrease of internal resistance. More significantly, the uniform chemical-electrochemical interface could be noted after numerous cycles. Given this, the work is expected to illustrate the regeneration effect of molecular groups, whilst providing controllably repairing strategies for S-LFP.