Polystyrene-b-[poly(ethylene oxide)]3 믹토암 스타 블록 공중합체의 합성과 특성 연구

Abstract

Lithium ion batteries (LIBs) have been widely investigated as one of promising devices due to long cycle life, high specific capacity and high cell potential. But recently LIBs have safety issue due to flammable liquid electrolytes. To overcome the safety issue, Polyethylene oxide (PEO) based electrolytes was discussed in order to substitute liquid electrolytes. Moreover solid polymer electrolytes based on poly(styrene-b-ethylene oxide) (PS-b-PEO) have intensively been investigated to improve the stability of lithium ion battery. Given that the PS-b-PEO block copolymers can be self-assembled into various nanoscale morphologies, intimately linked to their ion transport properties, more researches have been focused on the variation of block composition and molecular weight of PS-b-PEO block copolymers. In this study, I investigated morphology and ionic conductivity of PS-b-PEO3 miktoarm star block copolymers compare to PS-b-PEO linear block copolymers. PS-b-PEO3 miktoarm star block copolymers and PS-b-PEO linear block copolymers are synthesized by atom transfer radical polymerization (ATRP) and anionic polymerization. Their morphology was confirmed by small angle x-ray scattering (SAXS) experiments. Lamellar morphology was obtained in all cases. Lithium ionic conductivity is measured through electrochemical impedance spectroscopy (EIS). Conductivity values of PS-b-PEO3 were about 30 times higher than that of PS-b-PEO at ambient temperature. It was caused by low crystallinity of PEO in case of PS-b-PEO3. Crystallinity of PEO was demonstrated by differential scanning calorimetry (DSC). Additionally dynamic storage and loss moduli of polymers are measured by rheometer. It was found that the PS-b-PEO3 provided high mechanical properties at temperature below 50 ℃. Consequently, improvement of Li+ ion transport and mechanical properties is related to differences of polymer structure. So I conclude that chain structure of PS-b-PEO3 miktoarm star block copolymer is effective to improve ionic conductivity and mechanical properties.