Fiber supercapacitor using epoxy-based gel polymer electrolyte with high ionic conductivity and mechanical flexibility

Abstract

Recently, flexible energy storage devices have become an important issue for the smart textile market and flexible electric devices. Among them, fiber supercapacitors are one of the most promising candidates due to their light weight and mechanical flexibility. Traditional liquid electrolytes for fiber supercapacitors exhibit critical problems such as leakage when the device is deformed. On the other hand, solid electrolytes have a trade-off relationship between mechanical property for flexibility and ionic conductivity. Therefore, gel polymer electrolytes (GPEs) have attracted attention because of their sufficient ionic conductivity and high flexibility for maintaining their structure under bending, stretching, or twisting. However, liquid electrolytes in GPEs have a safety issue caused by narrow window voltage and flammability. Electrolytes with narrow window voltages could not provide the appropriate capacitance. To overcome this problem, ionic liquids that featured high electrochemical and thermal stability are used for GPEs. However, GPEs with ionic liquid have limited flexibility and ionic conductivity. In this work, we report a GPE comprising an ionic liquid and polyethylene oxide-abundant epoxy. The epoxy is synthesized from the crosslinking reaction between the amine with three-block copolymer and bisphenol A diglycidyl ether. The ionic conductivity of the fabricated GPE increased 2.0 × 10−3 S cm−1 at room temperature with increasing contents of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMImTFSI). Further, EMImTFSI gives an improvement of flexibility up to 107%. A fiber supercapacitor using developed GPE shows excellent electrochemical performance approaching using liquid electrolyte. In short, our result demonstrates that the GPE is a promising candidate for various applications involving multidirectional deformation such as fiber-type electric and flexible devices.