Supercapacitors are electrochemical energy storage devices that find use in many electronic devices as well as increased application in large high-power requirement devices. The primary advantages of using a supercapacitor are the fast charge/ discharge rates and the long cycling lifetime. Traditionally supercapacitors have utilized organic or aqueous electrolytes both of which introduce significant drawbacks. For example, organic electrolytes are flammable which creates safety considerations that need to be addressed while aqueous electrolytes are limited to the electrochemical stability of water (1.23 V). Ionic Liquids (ILs) are a growing class of electrolyte that offer increased thermal and electrochemical stability over standard electrolytes. Additionally, ILs are non-flammable and are non-volatile, eliminating the possibility of flammable devices. Despite the advantages of IL electrolytes, they are highly viscous and do not easily access the pores of the electrode material in supercapacitors. Most commonly, high surface area carbon is used as supercapacitor electrodes but is only effective if the pores are filled with electrolyte. It is expected that successful wetting of the electrode surface will make IL electrolytes competitive with the current state of the art. Here, new surfactant ILs are synthesized and assessed as the electrolyte in supercapacitors containing porous carbon electrodes.

The physical properties of ILs can be tailored by modification of the anion and cation structures. Here, a mixture of surfactant ILs was used as the electrolyte which is shown to offer enhanced capacitance over the parent ILs. Each surfactant IL was synthesized in house and characterized through NMR, TGA, as well as viscosity and conductivity measurements. Capacitance, calculated from the integration of cyclic voltammograms, is shown to depend on the concentration of each IL and temperature, which is attributed to the changes in viscosity and conductivity of the mixture. Improved capacitance in supercapacitors with porous carbon electrodes can be related to lower surface tension and increased wettability of the porous electrodes the surfactant IL additive. In addition we demonstrate a significant thermal operating window of the proposed electrolyte.