Tuning ultrafine manganese oxide nanowire synthesis seeded by Si particles and its superior Li storage behaviors

Abstract

The nanostructure and the dimension of materials greatly affect their performance and function. It is important to develop synthesis strategies that enable the control of the materials’ morphology and structure and further reduce their size. In the present work, we report a novel synthesis approach that utilizes Si nanoparticles for synthesizing ultrafine MnO nanowires. The resulting nanostructure comprises MnO nanowires with a diameter of ~5–10 nm embedded in an amorphous carbon matrix. X-ray diffraction patterns and high-resolution transmission electron microscopy images clearly reveal the growth mechanism of nanowires. As an anode material for the lithium-ion battery, the nanostructure exhibits excellent charge transfer kinetics and extremely high electrochemical performance, including reversible specific capacities of 285.9 mA h g−1 at 30 A g−1 and 757.4 mA h g−1 at 1 A g−1 after 1000 cycles. X-ray absorption fine structure (XAFS) confirms that the enhanced performance is related to the increase of the ordering of the O2− ions in the MnO structure during the charge/discharge processes. This novel synthesis strategy may inspire studies of other transition-metal-oxide nanomaterials with special orientation to tune their physical chemistry properties. By using silicon nanoparticles as seeds, a team in China has made ultrafine manganese oxide (MnO) nanowires in a matrix of amorphous carbon. The properties of nanowires vary according depending on their size and shape, and hence methods are needed for controllably synthesizing nanostructures and for shrinking their dimensions. Now, Dingguo Xia and co-workers at Peking University in Beijing have used epitaxial growth to synthesize MnO nanowires with diameters in the range 5–10 nanometres embedded in a carbon matrix. They characterized the growth mechanism and properties of this nanocomposite and found that it is promising as an anode material for lithium-ion batteries. In particular, it exhibited excellent charge transfer kinetics and electrochemical performance. The scientists consider that the synthesis strategy may be applicable for making nanostructures of other transition-metal oxides. It can be found that the Mn/Si ratio is a crucial factor affecting the morphology of the as-obtained products. The pristine Si nanoparticles are sphere-like particles of ~100 nm in diameter. When the Mn/Si molar ratio is 4:1, ultrafine MnCO3 nanowires less than 10 nm in diameter are obtained. The MnO@C nanowires were synthesized via polymerization–pyrolysis steps, and the excellent high-rate performance and stability of the MnO@C nanowires used as an anode in the lithium-ion battery are attributed to the unique interconnected nanostructure.