Characteristics of electric double-layer capacitors based on solid polymer electrolyte composed of sodium polyacrylate.

Abstract

Despite the low cost and high ionic conductivity of aqueous electrolytes, their practical applications are limited because a low withstand voltage of 1.2 V The energy density increases in proportion to the withstand voltage which is a crucial factor for electric double-layer capacitors (EDLCs) with solid polymer electrolytes. In this study, the electrolyte solution was made into a viscous solid polymer electrolyte to improve the withstand voltage of the electrolyte. The solid polymer electrolyte was prepared from sodium polyacrylate and doped with potassium hydroxide (KOH) and pure water. Sodium polyacrylate can absorb water at the temperature of 16-28 °C and exhibits suitable ion transfer. The EDLCs consisted of a distilled Japanese shochu-waste-activated-carbon electrode, a titanium mesh collector, and a solid polymer electrolyte. All the processes were performed at room temperature. Their electrochemical characteristics were measured using cyclic voltammetry (CV). From CV, the withstand voltage, cycle range, and specific capacitance were evaluated. The performance of the solid polymer electrolyte varied depending on the weight ratio of the constituent sodium polyacrylate and the molar concentrations of the KOH. Here, the value of molar concentration and its variation, depends on the weight ratio of the material. With the addition of sodium polyacrylate, the withstand voltage, which was 1.2 V, rose to over 2 V. Some of the samples increased up to 5 V. In the cycle measurement, the rate of decrease in capacity exceeded 20% after 250 cycles.