What is a SuperCapacitor and how does it work?

2019-09-09 [13:54]
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  A capacitor is a device that can store electrical energy. As shown in Figure 1, the capacitor basically consists of two electrodes facing each other.

When the DC voltage consisting of Anode and Cathode flows to two electrodes in the structure of Fig. 1, electric charges are collected and stored at each electrode. At this time, a current flows during the storage of the charge, but no current flows in the stored state.
   In addition to collecting electric charges and storing electrical energy, capacitors have a function of instantaneous current flowing through the capacitor when a DC voltage is applied to the capacitor. By using this function that cannot pass DC, it is used as a DC blocking device in electronic circuits.
In the case of alternating current, unlike direct current, the alternating current has the effect of continuously changing the anode and the cathode polarities.
  The capacitor is manufactured by putting an insulator between two electrode plates. At this time, various kinds of capacitors can be manufactured according to the material of the insulator, and there are also capacitors which use air as a dielectric without inserting anything.
  Recently, researches for applying nanostructures to capacitors have been conducted, and efforts have been made to apply carbon nanotubes as ionic states of liquids having polarity at the interface between a conductive solid electrode and an electrolyte. In addition, developing EDLC technology with high power and high energy density is conducted. If these research and development is completed, it is expected to increase the capacity of the capacitor.
   The unit representing the capacitance of the capacitor is used as the Farad (F). In general, since the charge capacity accumulated in the capacitor is very small, a unit of μF or pF is used, with the developing EDLC technology, SuperCapacitor capacitance is used as the units of F.
  Super capacitors are the capacitors with very high capacitance, also called ultra capacitors, as it has ultra-capacitance. In academic terms, it is called an electrochemical capacitor compared to the existing electrostatic or electrolytic capacitor. In Korea, when the national industrial technology classification system was reorganized in 2004, supercapacitors were defined as the ultracapacitor, the capacitor with ultra-capacitance

  Supercapacitors have been commercialized since the 1980s, but their development history is a relatively short period of time, but the technology development of new electrode materials such as metal oxides and conductive polymers including activated carbon and hybrid technology using asymmetric electrodes made much progress. Some announced supercapacitor to have energy densities exceeding Ni-MH batteries.
  The supercapacitor uses activated carbon with a large surface area and shortens the distance of the dielectric to achieve a very large capacitance in F units. In addition, sustaining overcharging and over-discharging does not affect the life of the battery as well as excellent environmental friendliness. As it is an electronic component that can be soldered on, there is no short circuit or connection instability like a secondary battery. Basically, the secondary battery uses the electrochemical reaction, whereas the supercapacitor uses the method of physically accumulating the charge itself so that the charge and discharge time can be controlled, and the long life and the high energy density can be obtained. 

  The charging or discharging energy by physical adsorption and desorption of electric charge on the surface of activated carbon is the supercapacitor principle as shown in Figure 2. It is a high output power source that supplies high current instantaneously or continuously after storing a lot of energy instantly. Supercapacitors have brought a dramatic increase in capacitance by using activated carbon (~ 3000m2 / g), as an electrode material, which increases the specific surface area per unit weight.

  The basic structure of the supercapacitor consists of a porous electrode, an electrolyte, a current collector, and a separator consisting of a positive electrode and a negative electrode as shown in Figure 3. By applying a voltage of several volts across the unit cell electrodes, ions in the electrolyte move along the electric field and act as an electrochemical mechanism generated by adsorption on the electrode surface. Supercapacitors have a relatively simple structure compared to secondary batteries.
  Electric Double Layer Capacitors (EDLCs) Related to an electric double layer formed at the interface of an electrode and an electrolyte, it consists of two polarizable electrodes. The charging and discharging principle show that charges are arranged at the electrode-solution interface as shown in Figure 4.

Source : Materials and Components Technology Network
Korea Institute of Science and Technology Information (KISTI)

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