Date: Tuesday, May 11, 2021
Time: 11:00 am
Talk Title: Engineering Polymeric Ionic Liquids for Metal Ion Conduction
Metal-ion rechargeable batteries are the technology of choice for numerous applications, yet the energy density and safety of commercial devices is often limited by using organic liquid electrolytes with high flammability and poor stability of electrode/electrolyte interfaces during operation. Ionic liquids are a class of functional liquid salts that address both voltage and thermal stability concerns. Incorporation of ionic liquid moieties onto a polymer to form polymeric ionic liquids (PILs) synergistically combines the functionality of ionic liquids with the mechanical robustness and mesostructured control imparted by the polymer backbone. I will discuss the design of ionic liquid-metal cation interactions and overall polymer design to create all solid-state polymer electrolytes with high ionic conductivity of Li+ as well as higher valency metal cations relevant to next generation batteries. These metal ion-IL interactions are frequently metal-coordination bonds that simultaneously act as reversible cross-links, lending additional mechanical strength. The metal-ligand bond lifetime therefore determines both the ionic conduction and the time-dependent mechanical properties. Further, this lifetime is shown to dominate performance to a much greater extent than other variables including polymer dielectric constant.
Structure control over soft matter on a molecular through nanoscopic lengthscale is a vital tool to optimizing properties for applications ranging from energy (solar and thermal) to biomaterials. For example, while molecular structure affects the electronic properties of semiconducting polymers, the crystal and grain structure greatly affect bulk conductivity, and nanometer lengthscale pattern of internal interfaces is vital to charge separation and recombination in photovoltaic and light emission effects. Similarly, biological materials gain functionality from structures ranging from monomeric sequence through chain shape through self-assembly. The Segalman Group works to both understand the effects of structure on properties and gain pattern control in these inherently multidimensional problems. We are particularly interested in materials for energy applications such as photovoltaics, fuel cells, and thermoelectrics.