Review of PVA-based gel polymer electrolytes in flexible solid-state supercapacitors: Opportunities and challenges

Flexible solid-state supercapacitors with high power density and rate performance, long cycle life, high safety and ease of fabrication are highly desirable. They can be used in an emerging market of flexible and wearable electronic gadgets. Gel polymer electrolytes are being considered as one of the best candidates. They typically have higher ionic conductivity than solid electrolytes without safety concerns of liquid electrolytes. This article reviews the latest achievements in the application of PVA-based gel polymer electrolytes for flexible supercapacitors and new findings on the improvement of their ionic conductivity, mechanical properties, and overall electrochemical performance. Several current kinds of research attempt to overcome these challenges with the main goal of improving ionic conductivity and electrochemical properties. There is no limitation for ionic conductivity of gel electrolyte because high ionic conductivity can lead to higher specific capacitance and also sufficient electrochemical performance. A recent study of gel electrolytes has shown the highest ionic conductivity of 82 mS.cm−1 for PVA/H2SO4/Glutaraldehyde/H2O which results in a large areal capacitance of 488 mF.cm−2 (100 reference).