Recycling Nd Magnet Scraps to Synthesize Carbon-Swaddled Fe3O4 Anode Material for Lithium-Ion Battery

Abstract

This study explores the innovative recycling of neodymium (Nd) permanent magnet scrap to synthesize Fe₃O₄, a high-capacity anode material for secondary batteries, by leveraging the Fe oxalate solution produced during recycling. The traditional process of recovering Fe from permanent magnets in the form of oxides produces products with limited economic viability and usability. For the first time, we have successfully synthesized Fe₃O₄ as an anode material for lithium-ion (Li-ion) secondary batteries from scrap Nd magnets. We address the existing challenge by employing a novel approach: hydrothermal synthesis of crystalline FeC₂O₄·2H₂O from the Fe leachate, extracted via oxalic acid leaching from a mixed phase of NdF₃-Fe₂O₃ controlled during fluorination heat treatment while recycling. The recovered FeC₂O₄·2H₂O is subsequently phase-transferred to Fe₃O₄ under an Ar atmosphere. To overcome the inherent low conductivity and rate capability of Fe₃O₄, a carbon-coating process utilizing dopamine HCl is implemented. The developed C-Fe₃O₄ anode material exhibits a significant capacity retention of 428 mAh/g after 500 cycles at 1C, showcasing its potential for use in high-performance secondary batteries and contributing to the sustainable recycling of critical materials.