Free Standing Flexible Lithium-Ion Polymer Electrolyte Membranes formed by Photopolymerization

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TECHNICAL SUMMARY: The principal objectives of this project are (1) to demonstrate how the fundamental understanding of ternary phase diagrams may provide guidance to facile fabrication of free-standing flexible polymer batteries and (2) to elucidate governing principles for creation of periodic arrays of ionic channels aligned homeotropically via photolithography and having well defined domain size and periodicity. These aligned channels produced by photopolymerization-induced phase separation will not only serve as ion conducting wires (or micro-channels), but also increase the ion concentration without sacrificing the mechanical strength and integrity of the free-standing battery membranes. Such periodic arrays of channels with perpendicular orientation have been highly sought for enhanced electron/exciton transport in the development of organic materials for solar cell applications as well as for efficient Li+ ion transport in rechargeable polymer batteries. This project focuses on determination of the eutectic phase diagram as a means of suppressing and/or eliminating undesirable constituent crystals in the binary and ternary mixture of polyethylene glycol diacrylate (PEGDA)/succinonitrile (SCN)/lithium bis-(trifluoromethylsufonyl)imide (LiTFSI). The uniqueness of the present system is that photolithographic crosslinking of PEGDA not only affords improved mechanical strength and integrity of the networks, but also increases the ion transport through the unperturbed channels. Moreover, the aligned oriented channel structure will also increase the ion storage capacity due to increase in interface areas and complexation with nitrile groups of SCN. Another advantage is that SCN can effectively ionize the ionic salts and also completely eliminate the undesirable LiTFSI crystals. More importantly, the fabricated polymer electrolyte membrane is a free-standing film that requires no organic solvent and has a high conductivity (7.1x10-3 S/cm) at ambient temperature. The fabricated polymer electrolyte membrane may be operated over a wide temperature range, from 40-80 deg C.NON-TECHNICAL SUMMARY: The goal of this project is to study and develop lightweight and rechargeable free-standing polymer lithium ion batteries for "green" electric vehicles. Unlike conventional electrolyte batteries, the present polymer electrolyte membrane contains no toxic or flammable organic solvent and thus the safety issue such as solvent leakage or battery combustion may be avoided. The present polymer electrolyte is moldable in any shape or form, and thus it should find broader utility. The strategy of the perpendicular alignment of cylindrical columnar morphology along the film thickness direction will further improve ion transport through the channels and enhance ion storage capacity due to increase in surface/interface areas. The knowledge thus acquired can be transferred beyond the scope of the current project, specifically to development of organic materials for solar cells and photo-optical switching in information technology. This project will educate graduate and undergraduate students who will be exposed to multi-disciplinary research in polymer materials science, engineering mathematics, and electrochemistry. The research outcomes will be disseminated to the public through the PI's website or distance-learning programs of the Akron Global Polymer Academy, which conducts workshops for high-school science teachers and their students.