Fe₃O₄@Fe Core–Shell Okara-Derived Activated Carbon for Superior Polysulfide Control in Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries offer high energy density but suffer from a polysulfide shuttle effect, leading to capacity fading and poor cycling stability. To address this, the Fe3O4@Fe core–shell Okara-derived activated carbon (Fe3O4@Fe-AC) using a sustainable and scalable approach with okara, a soybean residue, as the carbon precursor was developed. Electrochemical tests demonstrate that Fe3O4@Fe-AC/S cathodes exhibit superior cyclic stability, achieving an initial discharge capacity of 755 mAh/g at 0.5C and retaining 572 mAh/g after 500 cycles, with an ultralow capacity decay rate of 0.050% per cycle. At a high rate of 3C, the battery delivers an initial capacity of 557 mAh/g and retains a capacity of 367 mAh/g after 500 cycles, highlighting its excellent rate performance and low polarization potential. This composite enhances battery performance by integrating high-surface-area activated carbon for physical polysulfide adsorption, Fe3O4 for dipole–dipole interactions, and metallic Fe for catalytic LiPS conversion. With its high electrochemical performance, cost-effective synthesis, and sustainable precursor, Fe3O4@Fe-AC represents a promising material for practical Li–S battery applications.