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

Abstract

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.