The main advantage of ultra capacitors is that they have high energy density as compared to conventional batteries. Moreover, ultra capacitors are bio degradable and can be used for both small portable electronic items and also huge aircrafts.
Super capacitors, as they are also known, are double layer capacitors with electrolytic solution. The polarized solution stores energy inside the capacitor. It is to note that no chemical reaction takes place inside the solution as it does inside a conventional battery. Moreover, this mechanism is also reversible, which means that ultra capacitor can store and discharge electricity hundred times to that of conventional batteries.
This high electricity storage capacity is possible because of two main reasons. Firstly, ultra capacitors use porous carbon electrodes, which increases the surface area and thus allow more energy storage. Secondly, it has a dielectric capacitor which creates a small charge separation, allowing maximum storage of power throughout the capacitor.
Just check out the diagrams below which show the construction schematic of a single cell and a series arrangement of such cells