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Unlike ordinary capacitors, supercapacitors do not use a conventional solid dielectric, but rather, they use electrostatic double-layer capacitance and electrochemical pseudocapacitance, both of which contribute to the total energy storage of the capacitor.
The operating voltage range of a standard capacitor is very high, but for supercapacitors, it is between 2.5 and 2.7 V. The electrochemical supercapacitors are classified into three categories based on the charge storage mechanism: (1) electrochemical double-layer capacitors (EDLCs), (2) pseudocapacitors, and (3) hybrid capacitors.
The supercapacitor, also known as ultracapacitor or double-layer capacitor, differs from a regular capacitor in that it has very high capacitance. A capacitor stores energy by means of a static charge as opposed to an electrochemical reaction. Applying a voltage differential on the positive and negative plates charges the capacitor.
Contemporary usage sees double-layer capacitors, together with pseudocapacitors, as part of a larger family of electrochemical capacitors called supercapacitors. They are also known as ultracapacitors. The properties of supercapacitors come from the interaction of their internal materials.
The capacitance value of a supercapacitor is determined by two storage principles: Double-layer capacitance – electrostatic storage of the electrical energy achieved by separation of charge in a Helmholtz double layer at the interface between the surface of a conductor electrode and an electrolytic solution electrolyte.
In comparison, the self-capacitance of the entire planet Earth is only about 710 µF, more than 15 million times less than the capacitance of a supercapacitor. While an ordinary electrostatic capacitor may have a high maximum operating voltage, the typical maximum charge voltage of a supercapacitor lies between 2.5 and 2.7 volts.
Supercapacitors have a specific power 5 to 10 times greater than that of batteries. For example, while Li-ion batteries have a specific power of 1 - 3 kW/kg, the specific power of a typical supercapacitor is around 10 kW/kg.
