Ionomers based on polar monomers are an important class of energy materials for applications that require single-ion conduction. In this research, three novel types of materials are being made: (1) High molecular weight Reversible Addition-Fragmentation chain Transfer (RAFT) ionomers that are random copolymers of an anionic monomer and a polar solvating monomer, (2) RAFT diblock copolymers with one ionomeric random copolymer conducting block and one structural block and (3) polar low-Tg (glass transition temperature) non-volatile plasticizers. By fully understanding the dielectric and viscoelastic response of the RAFT copolymer ionomers, the optimal compositions for conduction of Li counterions will be identified and then RAFT diblock copolymers will be prepared with identical composition of the soft block. In this way, the effects of confinement to lamellar or cylinder phases can be identified, using also X-ray scattering to detail morphology. The linear viscoelastic response of these polymers will be understood using simple extensions of Rouse and reptation models to include the effects of ion association lifetimes. Polar low-Tg non-volatile plasticizers will be added to those materials to boost ion conductivity and dielectric constant of the soft domains, while lowering Tg. Thus far, siloxane oligomers with polar solvating side chains seem best, owing to their very low T (between -80 C and -60 C). By exploring the parameter space of ion content, polarity and specific solvation ability of both the comonomer and the plasticizer, the goal is to guide future materials design in the energy materials arena. For the diblock copolymers the modulus near room temperature is also crucial and the effects of these parameter variations on modulus will be measured to understand the tradeoff between ion conduction and mechanical properties, and their link to morphology and the amount of plasticizer in each microphase.
NON-TECHNICAL SUMMARY:
Applications that will be enabled by new materials in the energy arena simultaneously require high conductivity of one (and only one) type of ion and good mechanical strength. This research on ion conduction and mechanical properties of polymeric energy materials aims to understand the structure-property relations in polymers that conduct only one type of ion, such as lithium for advanced batteries. One strong advantage of developing materials for lithium ion transport that only conduct lithium (single-ion conductors as opposed to the lithium salts used in batteries today that also must conduct a negatively charged ion) is that both battery charging and access to the power of the battery could be as much as 100 times faster. If successful, the fundamental knowledge generated from this research will result in the understanding needed to design polymeric materials for a variety of specific energy applications, including advanced batteries, fuel cells, solar cells, ionic actuators, supercapacitors and energy harvesting devices; each of which require ion transport and mechanical strength. These applications offer societal benefits that may improve the lives of humans across the globe. Additionally, the project will involve education and training of graduate and undergraduate students.
