A Low Temperature Inorganic Molten Salt Supercapacitor

Abstract

Porous activated carbon is an important electrode material for devices such as supercapacitors, batteries and fuel cells. Despite the research and commercialization work that has been carried out, there is still a need to understand some of the fundamental characteristics of the role of activated carbon and the electrolyte in charge storage and ion migration within these structures. There has been two general types of electrolytes used; aqueous electrolytes with high concentrations of conductive salts and organic electrolytes modified to be conductive or directly conductive as in the form of ionic liquids. The former have high ionic conductance, the latter have a larger voltage range for stability. In this work we introduce an alternative to theses electrolytes, a low temperature molten inorganic salt. Potential advantages include high conductivity and a large potential operating range. The work demonstrates that inorganic salts can be used as electrolytes in supercapacitors at temperatures as low as 120oC . The charge discharge characteristics were similar to aqueous electrolyte performance and higher charging voltages than the aqueous limits are possible. The work also showed that the activated carbon pore sizes that can be used for charge discharge are similar for the molten salt ions and the aqueous ions.