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Title:Development and characterization of next generation batteries
Author(s):Shin, Minjeong
Director of Research:Gewirth, Andrew A.
Doctoral Committee Chair(s):Gewirth, Andrew A.
Doctoral Committee Member(s):Nuzzo, Ralph G.; Kenis, Paul J. A.; Rodríguez-López, Joaquín
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Energy Storage
Rechargeable Batteries
Next Generation Batteries
Abstract:Advances in electrochemical energy storage technology have the potential to revolutionize every aspect of society from transportation to the power grid. Despite significant advancements in Li-ion batteries over the last few decades, the current Li-ion battery has almost reached its limit in terms of energy density. Even when fully developed, the highest energy density the Li-ion battery can deliver is not enough to meet the market demand for the transportation sector. Thus, exploring new battery chemistries beyond Li-ion is crucial to electrify transportation and enable grid electricity storage. The work in this dissertation describes approaches to develop and improve next generation battery systems by establishing structure-property relationships that govern battery performance. Chapter 1 provides the foundation to understand operating principles and related challenges of the rechargeable battery systems. Chapters 2 and 3 describe the redox chemistry of Li−S battery and strategies to mitigate the dissolution of sulfur species during electrochemical reaction. Chapter 4 describes the degradation mechanism of Ni-rich lithium nickel cobalt manganese oxide cathode materials for advanced Li-ion battery. In Chapter 2, the use of highly concentrated solvate electrolyte and the effect of adding hydrofluoroether (HFE) cosolvent on the cycling performance of Li−S battery is discussed. In order to evaluate interactions that might change Li−S battery properties, four different HFEs with varying degrees of fluorination were examined as cosolvents in the (MeCN)2−LiTFSI solvate electrolyte. The use of different HFEs enables fine tuning of Li+−solvent interactions which affect the cycling stability of the Li−S cell. Indeed, the cyclability of the Li–S cell varies depending on the HFE cosolvent, where the addition of highly fluorinated HFEs exhibits better capacity retention relative to the cells with less fluorinated HFE cosolvents. The origin of this HFE effect is evaluated using various surface and bulk analytical techniques coupled with computational methods. Results show that the lower polysulfide solubility in certain solvate:HFE solutions results in stable cycling and higher capacity as limited crossover of polysulfides generates cleaner Li anodes. Using sparingly solvating electrolyte is efficient in decreasing polysulfide diffusion, however, the Li−S battery chemistry is still dictated by the very low but non-negligible polysulfide solubility in solvate electrolytes. Another promising approach to afford Li−S battery chemistry without producing polysulfide intermediates is to utilize inorganic solid electrolytes (SE). The performance of all-solid-state Li−S battery using SE, however, is much worse than Li−S cells with liquid electrolytes in terms of active material utilization and rate capability. The major issue hindering the development of all-solid-state Li−S battery is the poor interfacial properties at the solid electrolyte/electrode interfaces. In Chapter 3, the strategy of modifying the interface to develop high performance solid-state Li−S battery is discussed. The highly concentrated solvate solution was employed as an interlayer material at the solid electrolyte/electrode interfaces, in order to form a favorable ionic contact while maintaining the nonsolvating property of the solid electrolyte. The incorporation of the interlayer enhances the cyclability of the solid-state Li2S cell compared to the bare counterpart. Electrochemical impedance spectroscopy of the interlayer-modified cell shows a gradual decrease in interfacial resistance as a function of cycle number, whereas the cell impedance of the bare cell remains constant. Another method to utilize the solvate electrolyte is to premix the solvate with SE to yield a solvate–solid electrolyte mixture (solvSEM) electrolyte. The hybrid Li2S battery using solvSEM electrolyte further improves the battery performance in terms of active material utilization, capacity retention, and active material loading. The solvSEM electrolyte combines the benefits of solid electrolyte and liquid electrolyte in that solid electrolyte acts as a blocking layer for polysulfide diffusion while solvate electrolyte forms the favorable ionic contact at battery interfaces. In Chapter 4, the effect of water treatment on the structure of lithium nickel cobalt manganese oxide (NCM) cathode materials is investigated. Three different compositions of varying Ni, Co, and Mn content were evaluated systematically. Following water treatment, the recovered NCM materials and supernatant solutions were analyzed using various spectroscopic techniques. After water exposure, the surface impurities such as Li2CO3 and LiOH dissolve and leach out into solution where the concentration of dissolved Li+ species is higher in Ni-rich NCMs. This result suggests that the thickness of the Li-rich surface layer is greater in high Ni-NCMs relative to the low Ni-NCMs and thus more susceptible to dissolution. Extensive exposure of NCM to water leads to chemical delithiation resulting in electronic and structural changes including Ni oxidation and an increase in the amount of near-surface lattice O2- in high Ni content NCMs.
Issue Date:2019-11-25
Rights Information:Copyright 2019 Minjeong Shin
Date Available in IDEALS:2020-03-02
Date Deposited:2019-12

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