Abstract:

With the increasingly widespread adoption of electronics into everyday objects with the introduction of the Internet of Things, the need for smaller, more efficient, and more robust energy storage devices is greater than ever. In this dissertation I discuss the development of a method of fabrication of nanoscopic thin films of niobium (V) oxide, Nb2O5, an intercalation material for Li-ion supercapacitors and batteries. Electrophoretic deposition from a colloidal solution of amorphous NbOxnanoparticles followed by calcination resulted in crystalline thin films of orthorhombic T-Nb2O5 with an inherent mesoporosity imparted by the electrophoretic deposition process. These films were evaluated electrochemically and were determined to have extraordinarily high energy storage metrics, however with repeated cycling these favorable metrics diminished. The high performance of Nb2O5 for Li-ion supercapacitors prompted an investigation of the mechanisms of capacity degradation over tens of thousands of charge/discharge cycles using electron microscopy, x-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and other methods. The result of these studies illustrated that there were two parallel causes of capacity degradation in Nb2O5 thin films: delamination of the active material from the current collector, and the progressive loss of crystalline structure associated with repeated insertion and extraction of Li-ions from the T-Nb2O5 lattice. After completing the degradation study of Nb­2O5 I turned my attention to understanding the electrochemical performance of manganese (II) sulfide, MnS, a conversion material for Na-ion energy storage. To do this I standardized a procedure for the electrodeposition of MnS thin films using the electrochemical quartz crystal microbalance technique. I then developed a method for the fabrication of core@shell Au@MnS nanowires. Comparison of the electrochemical performance of the thin film and nanowire samples with equivalent thicknesses show that the nanowire morphology imparts enhanced rate capability and improved energy storage metrics relative to thin films for high power applications.