Capacitance Degradation in Hydrogel Electrolyte Containing Magnesium-ion Conducting Water-in-Salt Solution

Abstract

For the purpose of fabrication of novel all-solid-state supercapacitor systems, compatibility of a gel polymer electrolyte consisting of “water-in-salt” aqueous solutions of magnesium bis(trifluoromethane sulfonyl)imide in polyacrylamide matrix was compared with the lithium analogue via symmetric supercapacitor cells. Although the lithium gel electrolyte promotes an irreversible plateau at around 1.5 V during initial charging of a carbon nanofiber based cell, reversible charge–discharge can be up to 2.0 V for an activated carbon based cell. Magnesium gel electrolyte promotes charge–discharge at the first cycle. However, during subsequent cycles, the cells show severe capacitance degradation, probably because of Mg(OH)2 precipitation at the negative electrode.

Keywords

• hydrogel electrolyte
• supercapacitor
• water-in-salt solution