Microsupercapacitors (MSCs) are microfabricated energy storage devices that utilize the rapid adsorption and desorption of ions at the electrode/electrolyte interface to store charge or electrical energy. To enable a microscale size, potential for on-chip integration with other electronics, and more rapid charge/discharge rates, MSCs are microfabricated with planar interdigital electrodes which differs from the conventional stacked electrode architecture of typical supercapacitors. Instead of a polymer-based separator, MSCs utilize the air or spacing between the interdigital electrodes as the separator. Compared to thin film batteries, MSCs have advantages such as higher power density and extended cycle life, but the energy density is lacking. As a result, these miniaturized devices are attractive for use as energy storage components to continuously power Internet of Things (IoT) devices, sensors, as well as other self-powering electronics. Carbon nanomaterials have been commonly used as electrodes due to their porous structure and high conductivity. The porous structure provides high surface area for ion exchange, leading to high capacitance. Additionally, these surfaces could be functionalized by transition conducting polymers, metal oxides, or metal nitrides to increase capacitance via pseudocapacitance. Pseudocapacitive materials stores charges via Faradaic reversible redox reactions at the electrode surface. In this study, we expect that incorporating thin and conformal coatings of pseudocapacitive materials onto vertically oriented carbon electrodes will increase the specific capacitance and energy density per area of the 3D MSC device by orders of magnitude while maintaining the conventional advantages of high power density and capacitance retention oven tens of thousands of charge/discharge cycles.

The goal of this study is to improve the energy density and capacitance of 3D MSCs, through novel fabrication method and coating design. This research will explore several novel methods and materials for fabricating nanostructured pseudocapacitive coatings on vertically aligned carbon nanotubes (VACNT) and graphenated carbon nanotubes (gCNT) based electrodes for use in high performance 3D MSCs. Various methods will be used to apply coating material to the carbon based MSC device in order to produce high energy and power densities. This work proposes a variety of approaches such as atomic layer deposition (ALD), electrodeposition, drop-casting and aerosol jet printing (AJP) to deposit pseudocapacitive materials on carbon based MSC electrodes. ALD is a relatively new high precision deposition method that pulses precursors to the substrate and forms conformal ultra-thin films with subatomic layer resolution in a subsequent half-reaction. Although there are numerous publications that demonstrate the use of ALD to deposit oxide or nitride thin films as pseudocapacitive layers for energy storage applications, these studies have been limited to electrode fabrication only. This project demonstrates the first full-cell 3D VACNT-MSC device via ALD of TiO2 and TiN.