Metals and Metallic Alloys for Energy Harvesting and Storage

Abstract

Metals have been widely used for harvesting and storing energy in devices such as superabsorbers and Li-ion batteries. However, incorporating metals into a wider range of energy applications is severely limited by their intrinsic optical and electrochemical properties. Therefore, in this thesis, we provide a new class of metallic materials by forming binary mixtures of Ag, Au, Cu, and Al with novel physical properties for photonics, and a comprehensive understanding of the fundamental electrochemistry in Al and Si anode all-solid-state batteries for energy storage.

The first part of my thesis focuses on developing metallic alloys with a tunable optical response. We realize a new family of metallic materials by alloying Ag, Au, and Cu with on-demand dielectric functions, which can be used in superabsorbers and hot carrier devices. We design and fabricate alloyed nanostructures with engineered optical response and spatially resolve the electric field distribution at the nanoscale by utilizing near-field scanning optical microscopy, which can potentially enhance the performance of optoelectronic devices. To understand the physical origin of the optical response of the alloys, we measure the valence band spectra and calculate the band structures of Ag-Au alloys, providing direct evidence that the change in the electronic bands is responsible for its optical property. Further, we obtain a photonic device with superior performance using metallic alloys. Specifically, an Al-Cu/Si bilayer superabsorber is reached in a lithography-free manner with maximum absorption > 99%, which can be used for energy harvesting.

The second part of my thesis highlights the importance of understanding the reactions and ion distribution in energy storage devices. We inspect how the Al electrode surface changes upon cycling and directly map the Li distribution in 3-dimensions within all-solid-state batteries by implementing time-of-flight secondary ion mass spectroscopy. This research indicates that undesired chemical reactions, including the formation of an insulating layer on the Al anode surface and the trapping of Li ions at the interfaces, hinder the cycling performance of the devices. Overall, our results will contribute to the design of energy storage devices with enhanced electrochemical performance.