Ionic liquid-based electrolytes for capacitor applications

In this work we have synthesized several novel ionic liquids (ILs) based on imidazolium/pyrrolidinium cations and maleate/phthalate anions. The 1.5 mol/L solutions of the ILs in gamma-butyrolactone (GBL) solvent were prepared as the electrolytes of electrochemical energy storage devices such as electrochemical capacitors and electrolytic capacitors. The conductivity, electrochemical stability, sparking voltage and thermal stability of these electrolytes have been investigated systematically in this work. The relatively high room temperature conductivity (up to 18.22 mS cm−1), wide electrochemical window (up to 3.6 V) and good high-temperature durability of the 1-ethyl-3-methylimidazolium and N,N′-dimethylpyrrolidinium cation-based electrolytes make them attractive for capacitor applications. In addition, these types of electrolytes could only be utilized in low-voltage type electrolytic capacitors due to their comparatively low sparking voltage (∼100 V). The temperature dependence of conductivity was also discussed in this study. The Vogel–Tammann–Fulcher (VTF) equation accurately describes the dependence of conductivity on temperature.