Influence of Synthesis Temperature on the Crystal Structure and Electrode Property of Sulfur-Doped Manganese Oxide Nanowires

Sulfur-doped manganese oxide 1D nanostructures with controllable crystal structures and crystallite dimensions have been synthesized via one-pot non-hydrothermal solution route. Powder X-ray diffraction analysis clearly demonstrated that the crystal structures of the sulfur-doped manganates can be tailored by the change of reaction temperature; layered δ-MnO₂-structured material was obtained at 60 °C while the reaction at 90 °C produced tunnel α-MnO₂ structured material. According to field emission-scanning electron microscopy, both sulfur-doped manganates possess 1D nanostructure-type morphology with the diameter of ∼20 nm and the length of ∼1 μm for δ-MnO₂-type material, and the diameter of ∼100 nm and the length of ∼800 nm for α-MnO₂-type material, respectively. From X-ray photoelectron and X-ray absorption spectroscopic analyses, sulfur ions exist as highly oxidized sulfate cluster on surface or grain boundary of the manganate crystallite whereas manganese ions are stabilized in octahedral geometry with the mixed oxidation state of Mn⁺³/Mn⁺⁴. Of special importance is that both sulfur-doped manganate nanowires show promising electrode performances for lithium secondary batteries.