High performance of regenerated LiFePO4 from spent cathodes via an in situ coating and heteroatom-doping strategy using amino acids

Abstract

In recent years, recycling of numerous spent lithium-ion battery cathode materials has received increasing attention in order to protect the environment as well as to conserve resources, and the recovery of spent LiFePO₄ (LFP) by direct regeneration has been widely studied. A considerable body of literature has delved into the failure mechanism of LFP. The mechanism is characterized by an irreversible phase change, which is primarily attributed to the sluggish diffusion of lithium ions (Li⁺) during cycling. Additionally, the migration of iron (Fe) ions to occupy Li⁺ sites further impedes Li⁺ diffusion. Consequently, the electrochemical performance of directly regenerated LFP is diminished by the phenomenon of Li defects. Here, a method of direct regeneration of LFP based on a doping strategy using environmentally friendly and economically efficient natural biomass amino acids has been developed, which inhibits Fe ion migration and improves the diffusion kinetics of Li⁺ and electrons by constructing a nitrogen-doped carbon coating. The regenerated LFP cathode exhibits excellent cycling stability and rate performance (98.7% capacity retention over 100 cycles at 1C current density and a high capacity retention of 87.9% after 500 cycles at 1C).