Towards scalable preparation of solid polymer electrolytes with cellulose nanocrystals

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WONG-DISSERTATION-2022.pdf (2.39 MB)
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Wong, Helen
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School of Chemical and Biomolecular Engineering
School established in 1901 as the School of Chemical Engineering; in 2003, renamed School of Chemical and Biomolecular Engineering
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https://hdl.handle.net/1853/72652
Abstract
Flexible power sources are essential to enable the autonomous operation of portable electronic systems. Conventional liquid electrolytes are not desirable for flexible batteries because of safety concerns surrounding the use of flammable organic solvents. A polymer electrolyte presents a promising alternative due to its higher mechanical integrity and lower risk of leaking solvent. Though having such advantages, these electrolytes have lower ionic conductivity compared to conventional liquid electrolytes. The thesis consists of three scalable processes for preparing polymer electrolytes with cellulose nanocrystals (CNCs). First, we demonstrate a “single-pot” synthetic approach that affords a flexible, free-standing solid polymer electrolyte comprising CNCs and a cross-linked interpenetrating polymer network. Polyethylene oxide (PEO) is blended with poly(ethylene glycol) dimethacrylate (PEGDMA), a lithium salt, and organic solvents to afford the cross-linked polymer electrolyte upon UV irradiation. The cross-linked PEGDMA matrix provides good mechanical properties, while PEO is known for excellent electrochemical stability and its ability to solubilize lithium salts. This approach can promote better CNC dispersion in the precursor solution. Also, the non-toxic cellulose additive contributes to good mechanical properties for serving as a reinforcing filler. When the cellulose nanocrystal content reached 10 wt% relative to the PEO fraction, ionic conductivity was retained compared to the PEO control. Second, the “single-pot” process was modified without flammable organic solvents. This “organic-solvent-free” approach is developed by integrating succinonitrile (SN) and low molecular weight polyethylene glycol (PEG) that has a multi-functional role in dissolving lithium salt and facilitating ionic conductivity. Because of the compatibility among the precursor components, CNCs were dispersed uniformly, even without organic solvents. Also, the addition of CNCs shares similar ionic conductivity characteristics to the “single-pot” approach. With no drying step needed to remove solvents, this synthesis is a more manufacturable alternative for having a shorter processing time. Third, the self-assembly of CNCs is examined in the application of polymer electrolytes. Free-standing CNC/PEG nanocomposites were prepared with evaporation-induced self-assembly (EISA). After the aligned membrane was synthesized, the polymer electrolyte solution was introduced in a two-step immersion by first swelling and then infiltrating the membranes with the lithium salt and lower molecular weight PEG. With the ionic conductivity demonstrated up to 0.059 mS/cm at room temperature, the aligned membrane could be a promising candidate for solid polymer electrolytes. Therefore, all the syntheses in the thesis provide paths toward scalable and sustainable processes that can lead to commercialization, producing polymer electrolytes with performance metrics suitable for smart packaging application that requires lower energy demand.
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2022-08-01
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