Ambient-pressure relithiation of spent LiFePO4 using alkaline solutions enables direct regeneration of lithium-ion battery cathodes

Lithium iron phosphate (LiFePO4) is widely recognized for its cost-effectiveness in manufacturing and high safety during usage, making it a favored choice for electric vehicles and energy storage stations. Nevertheless, the development of efficient and low-cost recycling methods has emerged as an urgent priority due to the economic and environmental benefits associated with it. Here, the present study successfully demonstrates the ambientpressure relithiation of lithium-deficient LiFePO4 particles in alkaline solutions. Specifically, the incorporation of reductive sodium nitrite with lower redox potential in the alkaline environment spontaneously repairs the compositional and structural defects, facilitating effective lithium-ion insertion back into the original site. Consequently, the short-term annealing step promotes the formation of more thermodynamically stable particles, resulting in enhanced cycling stability and rate capability comparable to that of the pristine materials. The regenerated LiFePO4 cathode exhibits improved electrochemical performance in terms of long-term cyclability, high-rate properties and reduced polarization (a high retention of 93 % after 1000 cycles at 5C). The findings of this study suggest the significant potential for utilizing various reductants in an alkaline environment to achieve ambient-pressure relithiation, thereby facilitating the recycling and remanufacturing of spent lithium-ion cathode materials.