Na-ion conducting gel polymer membrane for flexible supercapacitor application

A sodium-ion conducting poly(vinyl alcohol)-based gel polymer electrolyte membrane is developed by plasticizing with an ionic liquid , for the fabrication of electric double-layer capacitors. Sodium triflate is selected as the sodium salt. 1-Ethyl-3 methylimidazoliumtrifluoromethanesulfonate is employed as the plasticizer . The properties of the electrolyte membranes are analyzed in terms of their crystallinity , morphology, thermal stability, electrochemical stability window, ionic transference number, and ionic conductivity . The composition with poly(vinyl alcohol) - 30% sodium triflate + 10% 1-ethyl-3 methylimidazoliumtrifluoromethanesulfonate shows the optimal performances such as good thermal stability up to 150 °C and wide electrochemical stability window of 4.70 V. It is thus employed in the fabrication of electric double-layer capacitors, serving as both ion-conducting electrolyte and separator. The capacitor shows almost 100% coulombic efficiency and stable charge-discharge cyclic property with almost 100% capacity retention after 1000 cycles, when charging up to 1.6 V and 2.0 V with a specific capacitance of 103.7 and 127.8 F g −1 , respectively. It compares well with that made of a liquid electrolyte . This excellent performance is attributed to the sodium triflate with large-sized anions and thus high ionic conductivity (3.8 × 10 −3  S cm −1 ) of the electrolyte membrane.