장기화하고자 장치를 위한 이온성 액체기반의 고체 고분자 전해질

Abstract

Since the first observation of ionic conductivity in poly(ethylene oxide) complexes with alkali metal, solid polymer electrolytes (SPEs) have more advantages, compared to conventional liquid electrolytes in terms of lightweight design, high energy density, flexibility and mechanical stability, except for relatively lower ionic conductivity. Introducing ionic liquid having unique physical properties into polymer electrolytes has been considered as an imperative way to enhance ionic conductivity. Furthermore, the physical or chemical interactions between ionic liquid and polymer electrolyte could be used for adjusting the mechanical properties of polymer electrolyte through lowering glass transition temperature of host polymer resulting in the enhancement of polymer chain flexibility as well as ionic conductivity of the polymer electrolyte. In this study, therefore, the role of ionic liquid on ion conduction and morphology, of polymer electrolytes containing ionic liquids is thoroughly investigated for the development of advanced electrochemical devices. In order to increase ionic conductivity of solid polymer electrolyte, two different types of ionic liquids are selected: one is a neat ionic liquid as BMIM-TFSI and the other is weak binding lithium salts dissolved in BMIM-TFSI. To optimize mechanical and electrical properties, we study three different type of SPEs; epoxy-, thermoplastic polyurethane (TPS)-, and diblock copolymer-based SPEs. For the development of structural SPEs, epoxy-based SPEs can be prepared with one-pot synthesis via ring opening polymerization of epoxy-resin (YD128) as framework, PEGDE as plasticizer, BDMA as catalyst, and MeTHPA as curing agent, after three step thermal curing. We also utilize TPU with the hard and soft segments to simultaneously enhance ionic conductivity and stretchability. To provide such a multifunctional property, silica network is introduced in TPU via sol-gel reaction. The unique porous morphology of poly(styrene-block-2-vinylpiridine) (PSP2VP) diblock copolymer combining with ionic liquids is also explored. The nanopores can act as ion pathway where ionic can be fast diffused inside block copolymer. The incorporation of silica network into the block copolymer allows to create a hierarchically morphology, which can further enhance ionic conductivity by two orders of magnitude. Conducting ions concentration and mobility are simultaneously investigated, using electrochemical impedance spectroscopy. Glass transition temperature, measured by DSC, gradually decreases with increasing ionic liquid content. Mechanical strength such as Young’s modulus and elongation at break is systematically explored using DMA. These investigations are complementally by microstructural study from FE-SEM and EDS mapping.