Abstract
Energy storage is a fundamental requirement for utilising clean but intermittent renewable resources, maintaining a resilient power grid and powering a multitude of portable electric devices and systems. The work presented in this thesis investigates methods of filling the performance gap between electrochemical capacitors (EC) (commonly known as supercapacitors) and batteries; the former often have high power capability but low energy density while the latter often have high energy density but low power capability. Three approaches towards this are taken during this work: first, capacitance balancing of a traditional electrical double-layer capacitor (EDLC) type EC device is attempted by electrode material asymmetry; this approach advances upon previous techniques in which cells have electrode material symmetry but electrode mass asymmetry. The benefits of capacitance balancing were found to be improved device energy density and reduced capacitance loss during long term operation. Second, a novel type of lithium ion capacitor (LIC) which uses a silicon based negative electrode is developed. Such a device was found to offer high power capability (23 kW kg-1) while demonstrating an energy density of over 97 W h kg-1, both values are per total electrode mass. Third, layer-targeted spray deposition was used to deposit multi-walled carbon nanotubes (MWCNTs) at specific locations within an electrode structure. It was found that spray depositing MWCNTs at the outer electrode surface may increase its power capability. A consequence of this targeted deposition may be a reduction in the current collector material alongside improvements in energy storage and power capabilities.