Synthesis of one-dimensional NiFe₂O₄ nanostructures: Tunable morphology and high-performance anode materials for Li ion batteries

In this study, various controllable one-dimensional NiFe₂O₄ nanostructures including solid nanofibers, yolk/shell nanofibers and nanotubes have been successfully synthesized by a novel "electrospinning-hydraulic agitation" combined method. The morphologies, components and structures of different NiFe₂O₄ samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N₂ adsorption-desorption curve, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and inductively coupled plasma-atomic emission spectrometry (ICP-AES). A possible formation mechanism for the different morphologies was proposed based on the experimental results. More importantly, this method has been verified to be universally applicable for fabricating a variety of ferrite materials with tunable shapes, such as CoFe₂O₄, ZnFe₂O₄, CdFe₂O₄ and α-Fe₂O₃. Compared with the NiFe₂O₄ nanoparticles, solid nanofibers and yolk/shell nanofibers, the NiFe₂O₄ nanotubes exhibited a superior lithium storage capacity, which stabilized at an average capacity of 1349 mA h g^-1 even after 220 cycles at a current density of 100 mA g^-1. The unique one-dimensional continuous tubular nanostructures and the higher surface area of NiFe₂O₄ nanotubes deliver a prominent contribution to the excellent electrochemical performance.