Polymer gel electrolytes for flexible supercapacitors: Recent progress, challenges, and perspectives

With the rapid development of portable electronic products, wearable flexible energy storage devices such as flexible supercapacitors (FSCs) have attracted much attention. FSC devices possess various advantages, such as small size, flexibility and lightness, smooth operation, wide operating temperature range, and high energy density and power density. However, there are still significant challenges to make FSC devices in large-scale applications, such as poor gel electrolyte/electrode interface compatibility, poor cyclic stability under bending test conditions and low ionic conductivity of the gel electrolyte. Therefore, to develop FSC devices with outstanding characteristics, many efforts have been devoted to the development of polymer gel electrolytes which have excellent mechanical properties and electrochemical performance. This review aims to provide an overview of recent progress towards the development of advanced FSCs based on aqueous, non-aqueous, ionic liquid-based and redox gel electrolytes. We systematically discussed the challenges and future development of various gel electrolytes for FSC devices. Moreover, the development and performance evaluation of FSCs are also discussed.