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Ion Transport Phenomena at the Nanoscale in Different Model Battery Systems

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Lithium ion battery technology has flourished since its introduction into the consumer market. Not only has it helped revolutionize consumer electronics, it also compliments R&D into clean forms of energy harvest e.g. solar, wind, and hydro-electric. As demand for the technology grows, innovative approaches have been taken to improve capacity, output, and lifetime in Li-ion batteries. The approach studied in this research involves the inclusion of nanostructures, which have the potential to significantly increase capacity. While several techniques to fabricate nanostructures are understood, underlying phenomena governing ion transport in and around these nanostructures is only partially understood, which could directly impact design principles for such devices.

This thesis examines a variety of model systems which could serve to simulate environments found in proposed devices and answer questions regarding ion transport phenomena. The main components we studied from such battery systems were electrolyte and cathode materials. The electrolyte experiences different ion transport phenomena arising from the nanoconfinement of the cathode structures both around and inside the electrode material. Thus, having model systems to examine electrolyte and cathode material separately and in tandem is useful for elucidating phenomena without the challenge of deconvolution resulting from other current-carrying mechanisms.

Our main tools for carrying out our research were synthetic nanopores. The nanopore structures afforded means to access nanoscale, control environment, and even fabricate components for study. By studying the current-voltage curves in these systems, we were able to draw meaningful conclusions about mechanisms of ion transport in these model systems. The main findings of this research include the inducement of positive surface charge on nanopore structures by organic solvent-based electrolytes by means of dipole and/or ion adsorption, positive evidence of gel electrolyte fitting current models of ion current rectification, and the impact of oxidation state and cycling in cathode material on ion transport through its porous media. Each of these findings is directly related to the thrust of the research and potentially provide insights for future battery design.

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