Ionic liquid is a “salt” that is liquid at room temperature. A salt that is composed of ions has been thought to be solid at room temperature due to its high melting point like sodium chloride. However, ionic liquid, which is liquid at room temperature due to its low melting point, is a unique substance with properties that have never been seen in other known liquids. In recent years, applied research on various applications of ionic liquid has been under way because of its properties and the high designability of structures formed of a combination of anions and cations.