Energy materials based on single-ion conducting polymers mixed with zwitterions

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NON-TECHNICAL SUMMARY: Applications that will be enabled by new materials in the energy arena simultaneously require maximal conductivity of one and only one type of ion. This research on ion conduction and dielectric constant 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 and perhaps larger mobile ions for supercapacitors, sensors, and mechanical actuators. A way to increase the mobility of the conducting ions is to add "zwitterions", which are small molecules containing both positive and negative charges, to single-ion conducting polymers. Although the method of adding zwitterions to polymeric materials has shown promise, fundamental insight is needed to design materials for specific functions for future applications. 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 maximizing ion transport). Each of those applications has the potential to change current technologies and improve the lives of humans across the globe. This project will also provide advanced scientific training and exposure to interdisciplinary research to graduate and undergraduate students, as well as opportunities for outreach.TECHNICAL SUMMARY: Ionomers are an important class of energy materials for applications that require single-ion conduction, yet their structure-property relations are only beginning to be explored. In this research, three novel types of materials are being made: (1) High molecular weight polycations with conducting counter-anions that are homopolymers, random copolymers and diblock copolymers, (2) high molecular weight polyanions with conducting counter-cations that are homopolymers, random copolymers and diblock copolymers, and (3) polar small molecule zwitterions that are non-volatile plasticizers for both types of ionomers to boost ionic conductivity. A key fundamental question is how mixtures of ionomers and zwitterions can be optimized by careful molecular design of the two. If successful, this research will reveal the design rules for the codesign of ionomer and zwitterion. By fully understanding the dielectric response of these materials (including the temperature dependence of dielectric constant and ionic conductivity) and using X-ray scattering to detail their morphology, the effects of systematic variations in zwitterion structure in such mixtures will be understood in detail. By exploring the parameter space of ion content, counterion type and polarity (dielectric constant) of the zwitterion, the potential of this class of energy materials, in terms of highest possible dielectric constant and ionic conductivity, will be determined.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.