Chemical and Biomolecular Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2751
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Item ELECTROLYTE AND INTERPHASE DESIGN FOR HIGH-ENERGY AND LONG-LIFE LITHIUM/SULFURIZED POLYACRYLONITRILE (Li/SPAN) BATTERIES(2024) Phan, An Le Bao; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Lithium/sulfurized polyacrylonitrile (Li/SPAN) recently emerged as a promising battery chemistry with theoretical energy density beyond traditional lithium-ion batteries, attributed to the high specific capacities of Li and SPAN. Compared to traditional sulfur-based cathodes, SPAN demonstrated superior sulfur activity/utilization and no polysulfide dissolution issue. Compared to batteries based on layered oxide cathodes, Li/SPAN shows two significant advantages: (1) high theoretical energy density (> 1000 Wh kg-1, compared to around 750 Wh kg-1 of Li/LiNi0.8Mn0.1Co0.1O2) and (2) transition-metal-free nature, which eliminates the shortcomings associated with transition metals, such as high cost, low abundance, uneven distribution on the earth and potential toxicity. The success of Li/SPAN chemistry with those two critical advantages would not only relief the range and cost anxiety persistently associated with electric vehicle (EV) applications, but also have great implications for the general energy storage market. However, current Li/SPAN batteries still fall far behind their true potential in terms of both energy density and cycle life. This dissertation aims to provide new insights into bridging the theory-practice gap of Li/SPAN batteries by appropriate interphase and comprehensive electrolyte designs. First, the effect of Li/SPAN cell design on energy density and cycle life was discussed using relevant in-house developed models. The concept of “sensitivity factor” was established and used to quantitatively analyze the influence of input parameters. It was found that the electrolyte, rather than SPAN and Li electrodes, represents the bottleneck in Li/SPAN development, which explains our motivation to focus on electrolyte study. Another remarkable finding is that although not well-perceived, electrolyte density has a great impact on Li/SPAN cell-level energy density. Second, design principles to achieve good electrode-electrolyte compatibility were explored. Novel approaches to promote the formation of more protective, inorganic-rich interphases (SEI or CEI) were proposed and validated with proper experiments, including electrochemical tests, material characterizations (such as SEM, XPS, NMR, IR, Raman), and their correlations. Finally, based on the principles discussed in previous chapters, we developed a new electrolyte that simultaneously offers good electrochemical performance (Li CE > 99.4%, Li-SPAN full-cells > 200 cycles), decent ionic conductivity (1.3 mS cm-1), low density (1.04 g mL-1), good processability (higher vapor pressure than conventional carbonates, b.p. > 140 °C), and good safety. Outlook and perspective will also be presented. Beyond Li/SPAN, we believe that our findings regarding cell design as well as electrolyte solvation structure, interphases chemistry, and their implications on electrochemical performance are also meaningful for the development of other high-energy battery chemistries.Item ELECTROLYTE DESIGN FOR HIGH-ENERGY METAL BATTERIES(2022) Hou, Singyuk; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The demand for advanced batteries surged in the past decade because they are at the heart of several tactically important technologies, such as renewable electrification grids and electric vehicles (EVs). These technologies will progressively transform our energy consumption structure toward sustainability and alleviate the global climate crisis. Unlike consumer electronics, EVs require batteries with larger energy storage to avoid "range anxiety". According to the US Advanced Battery Consortium (USABC), breakthroughs are needed to double the battery energy density and reduce the price by 50% for EVs to be competitive in the automobile market. These stringent requirements are unlikely to be met by the Li-ion batteries (LIBs) because the charge storage limits have been reached. Metal batteries using metals as anodes require no host materials and have up to ten times higher charge storage capacities. When metals with low redox potentials (Mg, Ca, and Li) are used, new battery systems that benefit from larger capacities and high cell voltages result in over 100 % leap in energy density to satisfy the USABC's goals for EV applications. On the other hand, the scarcity of materials related to LIBs raises uncertainties and doubts in the transition to electric transportation. Metals such as Mg and Ca are highly abundant in the earth crust, which potentially ensures the reliability of the energy supply in the future.Despite the exciting prospects of metal batteries, there are knowledge gaps in understanding how the electrolyte changes the behaviors of metal plating/stripping. Although electrolytes are considered inert materials in batteries, they are indispensable in maintaining ionic transport, modulating interfacial reaction kinetics, and maintaining reversible electrode reactions through the formation of solid-electrolyte interphase (SEI). In this dissertation, I detailed our efforts to establish the microscopic understanding of the electrolyte structures, SEI components, nucleation, and growth of the electroplated metal with spectroscopic techniques and physical models. These understandings guided the design of electrolytes for reversible metal anodes in practical high-energy battery applications.Item Polymer-Ionic Liquid Hybrid Electrolytes for Lithium Batteries(2012) Fisher, Aaron Steven; Kofinas, Peter; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Intellectual Merit: The goal of this dissertation is to investigate the electrochemical properties and microstructure of thin film polymer electrolytes with enhanced electrochemical performance. Solid electrolyte architectures have been produced by blending novel room temperature ionic liquid (RTIL) chemistries with ionically conductive polymer matrices. A variety of microstructure and electrical characterization tools have been employed to understand the hybrid electrolyte's performance. Lithium-ion batteries are limited because of the safety of the electrolyte. The current generation of batteries uses organic solvents to conduct lithium between the electrodes. Occasionally, the low boiling point and high combustibility of these solvents lead to pressure build ups and fires within cells. Additionally, there are issues with electrolyte loss and decreased performance that must be accounted for in daily use. Thus, interest in replacing this system with a solid polymer electrolyte that can match the properties of an organic solvent is of great interest in battery research. However, a polymer electrolyte by itself is incapable of meeting the performance characteristics, and thus by adding an RTIL it has met the necessary threshold values. With the development of the novel sulfur based ionic liquid compounds, improved performance characteristics were realized for the polymer electrolyte. The synthesized RTILs were blended with ionically conductive polymer matrices (polyethylene oxide (PEO) or block copolymers of PEO) to produce solid electrolytes. Such shape-conforming materials could be lead to unique battery morphologies, but more importantly the safety of these new batteries will greatly exceeds those based on traditional organic carbonate electrolytes. Broader Impacts: The broader impact of this research is that it will ultimately help push forward an attractive alternative to carbonate based liquid electrolyte systems. Development of these alternatives has been slow; however bypassing the current commercial options will lead to not only safer and more powerful batteries. The polymer electrolyte system offers flexibility in both mechanical properties and product design. In due course, this will lead to batteries unlike any currently available on the market. RTILs offer quite an attractive option and the electrochemical understanding of novel architectures based upon sulfur will lead to further potential uses for these compounds.