Research on closed-loop recycling and regeneration technology of lithium-depleted LiFePO4 cathode waste

Abstract

Efficient recycling and regeneration of LiFePO₄ cathode waste from spent lithium-ion batteries is crucial for achieving resource recovery and promoting sustainable development. In light of the challenges associated with regenerating delithiated LiFePO₄ waste (delithiated slag) due to its elevated impurity levels, this study presents a closed-loop recovery and regeneration technology that leverages a coupled process involving sulfuric acid leaching followed by hydrothermal precipitation. By optimizing the sulfuric acid leaching conditions (concentration 2.5 mol/L, temperature 60 ℃, time 2.5 h, and solid–liquid ratio 1:10), the leaching rates of iron and phosphorus reached 94.95% and 95.68%, respectively. The leachate was treated with ammonia water (pH = 2, 60 ℃, aged for 2 h) to precipitate high-purity FePO₄ precursors. These precursors were subsequently utilized to synthesize regenerated LiFePO₄/C (LFP-B) cathode materials. The results indicated that the regenerated material exhibited an initial discharge capacity of 150.17 mAh/g at a rate of 1 C, along with a capacity retention rate of up to 90.67% after 500 cycles. Furthermore, its electrochemical performance was found to be comparable to that of commercial lithium iron phosphate materials. This study provides an economical and environmentally friendly technical solution to the problem of impurity interference in used LiFePO₄ batteries by constructing a closed-loop path of “delithiated slag → regenerated precursor → high-performance cathode material”, which is of great significance for promoting the recycling of lithium battery materials.