Safe, High-Performance, Polymer Electrolyte for Lithium Batteries

University Of Maryland, College Park, College Park MD

Investigators

Abstract

Abstract 1157590 Kofinas, Peter Intellectual Merit: One of the key barriers to the widespread use of lithium-ion batteries is their potential for catastrophic failure. When cells are thermally or electrically abused, their temperature can rise and exothermic reactions between the combustible, liquid electrolyte and the charged electrodes can cause the battery to combust, giving rise to safety concerns. While improvements in the electrode would ultimately make the future battery more energy efficient, requiring less active material, safety and shape are still largely controlled by the electrolyte. By combining a polymer electrolyte with ionic liquids, the resultant solid system will possess all the desired properties and be conductive enough to be useful as a battery, which will be inherently safe because there is no longer a flammable liquid component. Battery power would also benefit greatly from the conformal and safe nature of solid polymer electrolytes. The goal of this research is to better understand the electrochemical properties and microstructure of novel thin film solid polymer electrolytes with enhanced performance. Experiments have been designed to explore new ionic liquid chemistries, and at the same time fully characterize the electrochemistry and microstructure of the polymer IL blend, while developing a better understanding the nature of the solid electrolyte interphase (SEI). The following objectives will be pursued: 1. Never synthesized before IL chemistries will be developed consisting of sulfonium and tetrahyrdothiophenium architectures. The chemical structure of the novel ILs will be characterized using nuclear magnetic resonance and mass spectrometry. 2. Solid electrolytes consisting of polyethylene oxide (PEO)-based homopolymers and block copolymers of PEO blended with the synthesized ILs will be prepared via solution casting, and optimized for high power and energy delivery. 3. Upon optimization, a full electrochemical characterization will be completed to allow better understanding of the movement of lithium ions in the bulk and at the SEI. The SEI will be investigated by differential scanning calorimetry (DSC) and accelerated rate calorimetry (ARC), to determine the reaction rates and mechanisms of the constituent materials within the cell. AC impedance experiments will allow the determination of the bulk and interfacial resistance. Overvoltage studies will determine the stability of this interphase. SEM imaging and mass spectroscopy will identify the extent of the SEI and breakdown products. With the development of novel sulfur based ionic liquid compounds proposed in this research, improved performance characteristics are expected of the solid polymer electrolyte. Such shape-conforming materials could be easily wound up into coils or processed as coatings or sheets, thus providing large area devices with integrated electronics. Effectively understanding the mechanism behind the enhanced electrochemical performance of the proposed solid electrolyte systems will greatly benefit the design of the next generation of batteries. Broader Impacts: The broader impact of this research is that it will ultimately help push forward an attractive alternative technology to combustible and corrosive liquid electrolytes. The proposed polymer electrolyte system offers flexibility in both mechanical properties and product design. Ionic liquids offer an attractive option and the electrochemical understanding of novel architectures based upon sulfur will lead to further potential uses for these novel compounds. The solid-electrolyte interphase (SEI) is among the most important yet least understood elements of a battery. Further insight into the polymer electrolyte SEI, would enable the design of tailored interfaces for a future generation of safer batteries with longer lifetimes. This project bridges fundamental concepts of electrochemistry, polymer science, and chemical engineering. In addition to the impacts on science, the proposed project will also broadly impact engineering education, training students of different educational levels and from diverse backgrounds. This training will poise them for successful careers in a wide range of industries or academia. Findings from this work will be published in peer-reviewed journals and presented at professional meetings. Several initiatives are planned including specific programs that assist in undergraduate and graduate education, graduate student mentoring, and training of high school students from schools in minority-rich communities. The PI also plans to mentor a diverse undergraduate "Gemstone" team project on energy storage at the University of Maryland. Gemstone students are members of a living-learning community comprised of fellow students, faculty and staff who work together to enrich the undergraduate experience. This community challenges and supports the students in the development of their research, teamwork, communication and leadership skills. The mentored team of students will presents its energy storage project in the form of a thesis to leaders in the field, and the students complete the program with a citation and a tangible sense of accomplishment.