Core-shell structured Fe₃O₄@NiS nanocomposite as high-performance anode material for alkaline nickel-iron rechargeable batteries

In this work, novel core-shell structured Fe₃O₄@NiS nanocomposites with different NiS: Fe₃O₄ mass ratios, namely x wt.% Fe₃O₄@NiS, have been successfully synthesized by a modified sedimentation-oxygenation method, in which the NiS outer layer (∼4 nm) in-situ grown on the surface of Fe₃O₄ nanoparticles (∼30 nm). For comparison propose, pure Fe₃O₄ as well as NiS ex-situ modified Fe₃O₄ composites (x wt.% Fe₃O₄/NiS) are also prepared and studied. When evaluated the electrochemical properties as anode material, all of the Fe₃O₄@NiS nanocomposites exhibit much better performance than pristine Fe₃O₄ material, due to the inhibition effect of NiS layer for retarding the generation of Fe(OH)₂ passivation layer, which inevitably generates in the discharge process of the electrode and will hinder the OH⁻ getting deeper into the active particles for further electrochemical reactions. Contrast to Fe₃O₄/NiS, Fe₃O₄@NiS nanocomposites also display better electrochemical properties owing to their relatively completer and more uniform NiS coating layer. In view of the advantages of the designed in-situ nano core-shell structure as the facile controlled synthesis process and low cost of the raw materials, it is believed the environment-friendly and high-performance Fe₃O₄@NiS nanocomposite is a promising type of anode candidate material for iron-based alkaline rechargeable batteries.