Development of poly(vinyl alcohol) (PVA)-based sodium ion conductors for electric double-layer capacitors application

Abstract

In this work, ionic liquid, poly(vinyl alcohol) (PVA)-based sodium ion conductors were prepared by solution casting technique. The additives-free ion conductors illustrated poor ionic conductivity which is not applicable in any electrochemical device. Therefore, ionic liquid was added to improve the ionic conductivity of polymer electrolytes. Ionic liquid, 1-butyl-3-methylimidazolium bromide (BmImBr)-added solid polymer electrolytes comprising poly(vinyl alcohol) (PVA) and sodium acetate trihydrate (CH3COONa·3H2O) was investigated. The ionic conductivity of BmImBr-added polymer electrolyte (PE) showed an increment about five orders of magnitude from (1.07 ± 0.03) × 10−8 S cm−1 to (1.95 ± 0.01) × 10−3 S cm−1 with doping of 20 wt% of BmImBr under ambient temperature. The BmImBr-added PEs obey the Vogel–Tamman–Fulcher (VTF) theory. The plasticizing effect of BmImBr reduces the glass transition temperature (Tg) of the PEs. Complexation between PVA, CH3COONa·3H2O, and BmImBr was proven in Fourier-transform Infrared (FTIR) spectroscopy studies. Quantitative analysis of the interaction between PVA, CH3COONa·3H2O, and BmImBr was also scrutinized in FTIR study. The electrochemical potential window of the electrolyte was wider upon the addition of ionic liquid. Electric double-layer capacitors (EDLCs) were assembled. The assembled EDLC illustrated a specific capacitance of 0.684F g−1 with excellent electrochemical stability.