Proton-Conducting Polymer Electrolytes for Solid Flexible Supercapacitors
A typical solid polymer electrolyte consists of an ionic conductor, a polymer matrix, and additives. Heteropolyacids (HPAs) are excellent solid-state proton conductors at room temperature . One of the common HPAs is silicotungstic acid (SiWA, H4SiW12O40•nH2O).
We have developed a polymer-in-salt electrolyte system for supercapacitors using SiWA and polyvinyl alcohol (PVA). A systematic approach has been used to improve the performance of SiWA-PVA polymer electrolytes through additives and polymer structural modifications. The electrolytes showed excellent proton conductivity, stability, and film flexibility that enables thin and light weight solid supercapacitors (Fig. 1). They also outperformed Nafion® in terms of environmental stability at ambient conditions .
These SiWA-based polymer electrolytes have demonstrated high rate performance in both electrochemical double layer capacitors and pseudo-capacitors [3-5]. The solid polymer electrolyte-based devices were able to charge and discharge up to 100 Vs-1, with a time constant of 10 ms [3-5]. To further expand the potential window of the SiWA-based electrolyte, and thus increase the energy density, alternative HPAs have been synthesized. In this talk, proton conductivity and structural properties of the developed polymer electrolytes will be discussed. Device performance of different HPA-based solid supercapacitors will be presented and compared.
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Fig. 1. Photographs of (a) a HPA-based polymer electrolyte film and (b) an assembled flexible solid supercapacitor.