혼합 이온성 액체를 함유한 블록공중합체의 이온전도특성 연구

Abstract

Recently, polymer electrolytes containing ionic liquids have been attracting much attention because of their applicability to electrochemical devices such as lithium ion batteries, fuel cells, and electroactive actuators. Ionic liquids have many advantages such as high ionic conductivity, high electrochemical and thermal stability.Along with these ionic liquids, using block copolymers composed of an ionophilic domain and anionophobic domain as a polymer matrix, the ionic conductivity and mechanical durability can be achievedsimultaneously.However, practical application is impossible until now due to insufficient ion transport property.As factors affecting ion transport efficiency, there are morphologies, grain boundaries, dead end, and interfacial properties.Many studies have been carried out to identify and control them to improve ionic conductivity. Interfacial mixing ofionophilic and ionophobic domains of block copolymer is one of the main reasons of reduction ofion transport efficiency. Our group has already reported that the good ion transport efficiency can be achieved when ionic liquids were confined within ionic domains with a sharp interface, owing to the creation of less tortuous ion conduction pathway.In addition, the interfacial property and substructure of the lamellar structure are determined by the ion distribution within, and it can be controlled by varying the type of anion in the ionic liquids. Herein, I investigated ion transport properties of sulfonated block copolymers with lamellarmorphologies, which contain mixed ionic liquids. Lamellar morphology and substructure are identified by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), and ion distribution was identified by dynamic secondary ion mass spectroscopy (DSIMS). Although the ionic liquid has inherent high conductivity, if it forms tortuous conduction pathway when incorporated with the block copolymer, low conductivity is obtained by bad efficiency. ButI mixed this ionic liquid with another ionic liquid which forms less tortuous conduction pathway and introduced these mixed ILs into block copolymers. As results, improved ion transport propertieswere achieved by only mixing and introducing two ionic liquids into block copolymersdue to the efficient conduction pathway and inherent high conductivity.This creation of less tortuous conduction pathway is attributed to specific substructure and ion distribution within block copolymers. This work presentsfascinating experimental insights into interface-drivenmodulation of ion transport properties for polymer electrolyte, andthe ability to finetunethe conduct5ivity of IL-doped polymer electrolytes by varying composition of mixed ionic liquids could be the future avenue of designing desired polymer electrolytes.