Graduate Thesis Or Dissertation
 

High-Energy Lithium-Sulfur Batteries and Non-Metallic Ion Aqueous Batteries: Integrating Experiment and Theoretical Modeling

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/jw827k358

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  • Humanities have been craving more freedom and conveniences in whatever form. Carriages evolved to cars and ultimately to aircraft so that one can reach any place in the globe within a day. The mobile phone has enabled people to make a phone call without a need to find a phone booth, and laptops gave us conveniences to work outside of the office. Even with those benefits, people are still looking for more freedom by reducing the time of being connected to the charging stations to recharge batteries in your portable devices and even electrified transportations. To quench the thirst, a grand mission given to battery scientists is to boost up the energy density of batteries so that you can use your portable devices lengthy and drive farther without frequent charge. However, the current lithium-ion batteries (LIB) are facing capacity limitation due to the inherent Li storage performance of graphite and transition metal (TM) oxides. As a result, multiple promising Li-based chemistries were introduced during the past decade including lithium-sulfur (Li-S) batteries. Although those technologies promise more than five times of discharge capacity compared to that of state-of-the-art TM-based cathodes, their residence is still limited inside the laboratory due to the critical reasons that are usually being swept under the rug in academic-level researches. Not only the batteries for portable devices, but stationary batteries are also another important equipment to store electricity for household use and auxiliary power supply. As electricity has no shelf life, it translates into poor futuristic usage without proper storage devices albeit we feel it is ubiquitous these days. That is, the generation and consumption of electricity should come together, where the energy storage device is incongruous with the intermittency of the power generated from renewable sources. Pumped hydropower is a globally used method but a geographical requirement for the operation limits the wide applicability of it. Hence, rechargeable aqueous batteries, which are safe and cheap, are the best alternatives by ‘directly’ storing electricity while removing the location restriction and rendering us the time-independent options to utilize the resource. Especially, non-metallic charge carriers have not received attention as metal ions have been dominating the battery fields, which was deemed common sense. Here we suggest the possibility of using chemical waste to be utilized as the electrolyte source by showcasing prolonged rechargeable aqueous batteries using common acids as major electrolyte ingredients. To that end, high-energy Li-S batteries and cheap but safe aqueous batteries have been called for commercialization. Based on the purposes, different materials are applied for each type of battery, however, the all-encompassing underlying operation mechanism is more than similar: ‘chemical bonding’ of species inside the electrolyte and host electrode materials, which directly translates the performance of the electrochemical cells. Herein, this dissertation addresses three main topics. The first topic focuses on high-energy Li-S batteries towards a more practical-level under harsh conditions. In the first part, the synthesis of nano-sized ZnS crystals on the carbon/sulfur composites for better wettability of sulfur cathodes is introduced. In that work, we applied the facile coating method to the composite to enable the sulfur cathode work under the lean electrolyte regime, then its electrochemical performance and working chemistry are revealed. The second part describes a highly reversible lithium metal anode by introducing the secondary solvent, fluorinated ether, to be compatible with both anode and cathode for high gravimetric energy density Li-S batteries. The effect of co-solvent at the molecular level is studied to elucidate its chemical bonding between salts and solvents. Lastly, a full cell is tested under the practical level conditions, including lean electrolyte and the limited amount of anode that was not studied before. This information can be a good guideline for the development of feasible Li-S cells forward. The second topic presents theoretical modeling of non-metallic ion aqueous batteries. Here we used density functional theory (DFT) calculations to understand the unique chemical bonding between non-metal charge carriers and host materials. As stated before, simple acids were used as electrolytes and unexpected electrochemical performance was elucidated by exploring electron distribution via quantum chemistry-based modeling studies. We reveal proton, ammonium, and methyl viologen can be reversibly inserted via hydrogen bonds and exclusive host-guest interactions, where this finding can open a new avenue for the development of viable non-metallic ion aqueous batteries. The third part discusses integrating theoretical modeling with experimental results to distinguish the local Li environment in the layered LiMn0.5Ni0.5O2 for LIB cathode studies. We compared the experimental NMR spectrum and calculated NMR peaks based on particular TM orderings, where we can correlate the effect of annealing temperature in the experiment and composition of each TM arrangement. This information advises the new possibility of atomistic-scale interpretation by linking the DFT calculation and experimental NMR spectrum to comprehend the sub-nano scale world with confidence.
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  • Pending Publication
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  • 2021-02-01 to 2022-03-09

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