Hybrid nanocomposites for high-performance li-ion battery electrodes: Carboxylated polythiophene-based electrodes
Kwon, Yo Han
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This thesis describes systematic approaches to Li-ion battery electrodes: How methodical and structural consideration for both ion and electron transport coupled with electrode materials’ surface chemistries can contribute to high battery performance, enabling the realization of high-capacity Li-ion battery applications. In the first stage of the research, simple but crucial fundamental criteria have been identified. Both electron and ion transport are critical factors that determine the internal resistance of electrodes, which is the primary influence on electrochemical performance. Based on this idea, conjugated polymer electrodes were studied by introducing a water-soluble, carboxylate substituted polythiophene (i.e., poly[3-(potassium-4-butanoate) thiophene] (PPBT)). The PPBT π‒conjugated backbone and carboxylate (COO‒) substituted alkyl side chains, respectively, were attracted to the π‒electron carbon surface (e.g. carbon black, or CNT) and chemically interacted with the active material hydroxyl (‒OH) surface to form a carboxylate bond. Those interactions led to stable electrical networks, leading to the excellent electrochemical performance of carboxylated polythiophene-based electrodes. As a consequence, PPBT served as a polymeric binder, or a physical/chemical linker to render electroactive particles and carbonaceous materials (e.g. carbon black, or CNT) well-connected through specific molecular interactions, thereby yielding stable, high-performance battery electrodes. Findings pertaining to a new polymeric binder, electrode structure design, and material surface modification that are effective in battery performance are discussed.