Sulfur-Based Yolk-Shell Nanoparticles for Lithium Sulfur Batteries

The work presented in this dissertation focuses on the synthesis of gold-functionalized sulfur yolk-shell nanoparticles. Sulfur was chosen as a cathode material due to its high theoretical specific capacity (1675 mA h g−1). However, there are still many technical limitations for Li-S batteries, like the dissolution of the intermediate polysulfide and the large volumetric expansion of the material in the cell upon lithiation (~80%). Sulfur yolk-shell nanostructures were designed to improve the electrical performance of the lithium sulfur batteries. In the initial study, a sulfur@silica@porous gold yolk-shell nanostructure was chosen as the targeted nanostructure. The silica layer not only prevents aggregation, but also serves as an absorption layer to capture polysulfides. The porous gold layer was used to increase conductivity of the material. This unique yolk-shell nanostructure has the potential to enhance the performance of lithium sulfur batteries. This study has provided a template for the design and synthesis of yolk-shell nanoparticles with differing thicknesses of gold. In a separate study, gold was functionalized in the SiO2 shell of the sulfur yolk-shell nanoparticles. For this design, reducing the amount of gold was expected to increase the mass percentage of sulfur in the material battery. The cyclic and rate performance of the all the nanoparticles were tested. Additionally, other metal oxides, such as TiO2, can interact with polysulfide species through an adsorption mechanism, preventing their dissolution in the electrolyte and diffusion onto the Li anode. In a different study, we provide a template to synthesize various TiO2 nanoshells. All of the targeted nanoparticles reported herein were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and X-ray powder diffraction (XRD) spectroscopy.