Graduate Thesis Or Dissertation
 

Electrolyte Design: Improving Capacity and Structural Stability of Electrodes

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3t945z970

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  • The grand plan of carbon neutralization and COP26 in Glasgow require a quick shift of energy sources from conventional fossil fuel to a more renewable substitute such as wind, or solar energy. However, the intermittency of those renewable energy sources does not meet the demand of the energy, which requires batteries to bank the electricity when in surplus for later use when in energy deficit. Lithium-ion batteries (LIBs) have been leading the field due to its high energy and power density and such benefits are highly desirable for the application of portable devices (laptops, cell phones, etc.) and electrical vehicles (EV). However, the grid-scale energy storage devices prioritize safety, sustainability, and low cost over high energy density, thus making the LIBs not ideal as a solution for this scenario. Aqueous batteries, which use water as the electrolyte solvent, emerge as a competent candidate for grid-scale application. Such batteries possess merits of low cost, environmental friendliness, and sustainability at the expense of low energy density (narrow stability window of water). Aside from those merits, aqueous batteries often have diverse options of charge carriers: from monovalent (H+, Li+) to multivalent (Ca2+, Al3+, Zn2+), and from cationic to anionic (PF6-, TFSI-, super halides). Among those various charge carriers, proton exists as one of the oldest choices that are being re-investigated recently due to its ubiquitous nature, high rate performance, and low-temperature application. A plethora of materials have been identified as good electrode hosts such as metal oxides (MoO3) and Prussian blue analogs, however, due to the default choice of electrolyte to be aqueous acid, poor cycling stability, and severe HER/OER reaction have been observed in those studies. To solve this general problem in proton battery research, this dissertation elucidated that the inorganic acid H3PO4 could be dissolved and solvated by organic solvent – MeCN instead of water, such new proton electrolyte help prevent the structural deterioration of multiple electrode material with much better reversibility due to the absence of water decomposition. Other than protons, multivalent charge carriers also receive extensive research interest. Zinc ion batteries (ZIBs) stand out due to the appropriate striping/deposition potential of Zn2+/Zn (-0.76 V vs. SHE). Typical intercalation type cathodes for ZIBs include Vanadium based materials (V2O5, VOPO4), Manganese based material (MnO2, Mn2O3), and Prussian blue analogs, etc., and unfortunately, the vanadium-based materials are notorious for the structure collapse and dissolution problem during Zn2+ (de)insertion. To tackle this problem, this dissertation reported that by switching the charge carrier from Zn2+ to Fe2+, the VOPO4 structure is enhanced via iron bolting mechanism, which is induced by the interaction between V5+ and Fe2+, and consequently, much better cycling stability is achieved when storing Fe2+ than storing Zn2+. The most discerning aspect of aqueous batteries, that is, using water as the solvent, endows numerous advantages but also introduces problems to the system. The two most significant shortcomings are 1. Narrow stability window of water, and 2. Material deterioration and dissolution. To solve those, Wang et al. reported water-in-salt strategies of using high concentration salt to expand the window and help preserve the electrode material. Also, this dissertation shows that 30 m ZnCl2, which is a new water-in-salt electrolyte for ZIBs also helps avoid the dissolution of Ferrocene material, and achieve a Reverse Dual ion battery of using [ZnCl4]2- and Zn2+ as charge carriers, respectively. Other than using high concentration to expand the stability window, this dissertation also introduces another strategy, which is to bring the electrolyte to low temperature to convert water to a more stable Donor-Donor, Acceptor-Acceptor (DDAA) geometry. The 25wt% LiCl is chosen as the electrolyte due to its low freezing point, and the widened stability window of this electrolyte at -78 °C enables a full cell of 104 Wh/kg. Such low-temperature study could hold both practical usefulness as required for outer space activity and fundamental science since the water’s low-temperature behavior is mysterious to the electrochemists yet.
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  • Intellectual Property (patent, etc.)
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  • 2021-12-21 to 2024-01-22

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