A fundamental study of the interplay between ordered morphology, grain structure, and ionic conductivity in mixtures of block copolymers and lithium salts is proposed. The results of the proposed work have the potential to impact the development of high specific energy batteries with solid electrolytes. The work will focus on mixtures of polystyrene-polyethyleneoxide block copolymers, synthesized by anionic polymerization, and bis-trifluoromethylsulfonimide (LiTFSI), a salt that is often used in batteries containing polymer electrolytes. Small-angle X-ray scattering and depolarized light scattering will be used to determine the nature of the order-disorder and order-order phase transitions in these materials. Conductivity measurements will be made on the same samples as those used in the X-ray and light scattering studies using AC impedance spectroscopy. Measurements will be made over a wide range of block copolymer compositions, salt concentration, temperature, and annealing conditions.
NON-TECHNICAL SUMMARY:
The fundamental work proposed in this project is motivated by the need to design safe rechargeable batteries for clean energy-related applications such as electric vehicles and stationary energy storage. The proposed nanostructured ion-conducting solid will be used as the electrolyte in a lithium battery. By replacing the flammable liquid electrolyte that is used in current lithium batteries by a solid, one can use higher energy electrodes that, in turn increase the energy density of the battery. The absence of a flammable component makes the battery safe. The co-PIs will use solid-state batteries for demonstrations in their outreach activities involving high school students. Garetz works with the David Packard Center for Technology and Educational Alliances in New York City to mentor local high school students in fields related to technology and research. Balsara works with Math and Science Summer Academy program at Berkeley, and enrichment program which brings students from the Oakland School District to the University of California. The PIs will continue an ongoing collaboration with Professor M. Banaszak at A. Mickiewicz University, Poland on the subject of ion-containing polymers that arose from an NSF-sponsored workshop in Poland.
Technical accomplishments This is a collaborative project aimed at obtaining a fundamental understanding of a new class of electrolytes for lithium batteries. One of the limitations of current lithium batteries is safety. About one in ten million lithium-ion batteries exhibits catastrophic failure that is often initiated by combustion of the electrolyte. The electrolytes that we are studying are inherently nonflammable. In addition, they are mechanically rigid and tough, and this prevents deformation of the electrodes during battery cycling. The electrolytes are nanostructured, comprising ordered co-continuous domains of a hard polymer that gives the electrolyte the desired mechanical properties and soft salt-containing domains necessary for ion transport during charging and discharging the battery. The domains are formed spontaneously when the electrolyte is prepared by casting or melt-processing. We report on three fundamental discoveries related to the relationship between structure and properties of this class of electrolytes. When the ordered domains form from a homogeneous disordered phase, one obtains coexistence of order and disorder. This has important consequences on the manner in which the ordered phase forms. In nanostructured polymers without salt, the ordered phase grows until the entire sample is ordered. In nanostructured electrolytes, the initial growth of the ordered phase is followed by decay due to partitioning of the salt into the ordered domains. For practical applications, it is important to have a completely ordered electrolyte, and our work outlines regimes where this is possible. An important property of our electrolytes is the fact that the orientation of the domains is random; coherent order is restricted to regions that we call grains. We have, for the first time, established the relationship between grain structure and ion transport. The work described above was the fruit of collaboration between two research groups with complementary skills. The group at NYU Polytechnic School of Engineering specializes is characterization of grain structure while the group at UC Berkeley specializes in synthesis and characterization of ion transport. Student development and broader impacts The NSF funds were used to support one graduate student, Xin Wang, at NYU Polytechnic School of Engineering. He has received multidisciplinary scientific training in the crucial area of materials necessary for producing the next generation of batteries for transportation and other applications. The importance of this field is recognized by academia, industry, and national laboratories. The specific background in characterization of charge transport in nanostructured block copolymers is relevant for numerous other technologies. The work done by Xin Wang encompasses the characterization of polymers, optics, scattering, electrochemistry, and thermodynamics. Our collaborations with scientists at the national facilities (SSRL and APS NIST) have exposed Xin Wang and the UC Berkeley students to senior scientists with complementary backgrounds and research interests. Leveraging the nation's investment in research infrastructure for education of graduate students is a long-standing tradition in our groups. NSF funds also supported undergraduate student, Romana Amir, who received summer training in the characterization of polymers, optics, and light scattering. Throughout the course of this grant, the PI has been engaged in several activities that bring science to a wider audience. Since 2009, he has been a Directing Officer of the Brooklyn subsection of the American Chemical Society. Among the various activities of this group has been the organization and sponsorship of an annual public lecture called "Brooklyn Frontiers in Science" held at the NYU Polytechnic School of Engineering and aimed at a general audience. These lectures have been especially tailored to educate and excite students from various public and parochial high schools in Brooklyn. Recent speakers have been Jacqueline Barton, George Whitesides, Daniel Nocera and Sir Harold Kroto. Since 2005, the PI has organized a Distinguished Lecture Series in honor of retired Professor Herbert Morawetz, also directed toward a general audience, and covering all areas of science. Since 2006, the PI has also directed a Summer Undergraduate Research Internship Program in the Chemical and Biomolecular Engineering Department of the NYU Polytechnic School of Engineering. Significance and Societal Impact Lithium-ion batteries, used traditionally to power personal electronics, are being considered for powering electric vehicles, storing energy from the sun and wind, and for providing electrical power on airplanes. The electrolyte used in current lithium batteries is a flammable organic solvent. Safety concerns have limited the use of large format lithium ion batteries. Our research is related to the fundamental thermodynamic and transport characteristics of solid polymer electrolytes for lithium batteries. The electrolytes are nonflammable and thus have the potential to deliver energy more safely than current systems.
