Waste to value: Synthesis of efficient MnFe2O4 catalytic materials from spent LiMn2O4 cathode materials via FeSO4 reductive leaching and in-situ coprecipitation.

The economic and high-value recycling of spent lithium-ion batteries (LIBs) are essential for the sustainable use of natural resources and environmental conservation. This study introduces an innovative approach that integrates FeSO4 reductive acid leaching with in-situ coprecipitation to upgrade spent LiMn2O4 batteries into MnFe2O4 catalytic materials. Leaching experiments show that FeSO4, as an economical reducing agent, achieves over 98% leaching efficiency for Li and Mn under optimized conditions, replacing H2O2. During the reduction and decomposition of LiMn2O4, Fe2+ is oxidized to Fe3+, enabling the leachate to be directly utilized for coprecipitation without the need for additional iron supplementation. The resulting precursor is then roasted to produce MnFe2O4 catalytic materials. XRD, XPS, SEM, and TEM characterizations reveal that the roasting temperature significantly influences the microstructure size of MnFe2O4 and the cation distribution at octahedral sites. The sample roasted at 500 °C demonstrates the smallest particle size and the highest proportion of Mn3+ at octahedral sites, exhibiting excellent oxygen evolution reaction (OER) performance with an overpotential of only 324 mV (10 mA/cm2). This method efficiently integrates the recycling of spent LiMn2O4 batteries with catalytic materials preparation, offering a streamlined and effective recycling process for spent LIBs.