Materials and electrode configuration strategies for flexible, printable, and implantable energy storage
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Global energy consumption is projected to double from its 1990 level by 2030. Although rechargeable lithium-ion batteries have powered mobile computing and telecommunications for two decades, their energy density is inadequate to meet rising demands for grid storage, and falls short of DOE targets for electric vehicles and the needs of new electronic devices. As a result, the lithium-sulfur (Li-S) system has emerged as a leading “Beyond Lithium Ion” candidate. Simultaneously, the impetus for a comprehensive “Internet of Things” that interactively monitors and controls energy use, infrastructure, and human health has been consistently hampered by a lack of batteries that are small, thin, flexible, implantable, high-energy density, and cheaply manufactured to power the multitude of required devices. This dissertation addresses three aspects of these dilemmas. First, an elastic, conductive, and electroactive polymer nanocomposite comprising polypyrrole and polyurethane (PPyPU) is developed to serve as a binder for flexible Li-S cathodes. After fifty flex/bend cycles, the cathodes provide high capacity with essentially no capacity-fade for 100 cycles at high sulfur loadings. The electroactive PPy in the binder is believed to stabilize dissolved polysulfides, while the elastic PU accommodates the significant sulfur expansion which is known to compromise Li-S cathode integrity during charge/discharge. Second, a process is presented for producing extrusion-printed carbon nanotube-based electrodes for Li-S cathodes. Although printing provides a high-throughput, inexpensive, top-down, “green” alternative to industrial microfabrication, it has been infrequently applied to batteries, and the few reports of printed batteries were based on low energy-density materials. Therefore, multiwall carbon nanotube inks are formulated for printing microelectrodes to be utilized as electrodeposition scaffolds for high-loading Li/polysulfide catholytes. The resulting lithium-sulfur cathodes are shown to meet industrial benchmarks for portable and wearable electronics. In concert, sulfur-infused single-wall carbon nanotubes (S@SWNT) are used for inkjet-printed thin-film cathodes as proof-of-concept for integrated, printing-based nanomanufacturing. Third, an electroactive bio-nanocomposite comprising purely endogenous materials (dopamine and hyaluronic acid) is synthesized and characterized in vitro as a potentially implantable energy-storage material. The dopamine-hyaluronic acid (DAHA) hydrogel composite can be electropolymerized to create a pseudocapacitive biopolymer, p(DAHA), that exhibits catechol−quinone interconversion, high pseudocapacitance and discharge capacity, and stable, long-term electroactivity for 400 cycles. These characteristics predispose it for bioelectronic energy storage, i.e., as a supercapacitor or, when coupled with an implantable Ag/AgCl electrode, a biobattery with an operating voltage of ∼0.85 V.