Since ionic liquids (ILs) possess several attractive properties, including chemical and thermal stability, nonflammability, high ionic conductivity, and negligible vapor pressure, a new electrolyte system based on ILs has been proposed for chip type aluminum electrolytic capacitors. Four ILs based on imidazolium/pyrrolidinium cations and maleate/phthalate anions have been synthesized and their thermal stabilities have been examined. The 25 wt.% solutions of the four ILs in gamma-butyrolactone (GBL) solvent were prepared as electrolytes of chip type aluminum electrolytic capacitors. The conductivity, sparking voltage and thermal stability of these electrolytes have been systematically investigated. The results revealed that the four IL-based electrolytes exhibited high conductivity. Furthermore, the conductivity of maleate anion-based electrolytes is higher than that of phthalate anion-based electrolytes, whereas the high-temperature durability of phthalate anion-based electrolytes in conductivity is superior to that of maleate anion-based electrolytes irrespective of pyrrolidinium or imidazolium, cation. However, this type of electrolytes could only be utilized in low-voltage type capacitors due to their comparatively low sparking voltage. In addition, the capacitors utilizing the four IL-based electrolytes show excellent thermal stabilities during a reflow soldering process. (c) 2005 Elsevier B.V. All rights reserved.