Abstract:

Self-assembled microspheres of α-MnO₂ nanotubes were successfully synthesized by hydrothermal method using KMnO₄ and HCl as reactants, and H₂SO₄ and NH₄Cl as auxiliaries. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure and morphology of the products. The H⁺ and Cl^- ion concentrations substantially influence the crystal form of the product. Increasing either H⁺ or Cl^- ion concentration decreases the diameter of nanotubes but increases their length. In contrast, increasing both H⁺ and Cl^- ion concentrations, changes the product from α phase to β phase. Moreover, NH₄⁺ ion plays the key role of maintaining the product crystal and its tubular morphology. The electrochemical performance results showed that the microspheres of α-MnO₂ nanotubes with a unique morphology have a high first cycle discharge capacity of 1783.5 mAh·g^-1 at the current density of 20 mA·g^-1, along with a good rate performance. This suggests that the self-assembled microspheres were a promising material for lithium-ion batteries.

Key words: α-MnO₂ nanotubes, Controllable preparation, Self-assembled microspheres, Hydrothermal synthesis, Lithium-ion battery