Principle and Application of Supercapacitor


Super capacitors, also called Electrical Double-Layer C […]

Super capacitors, also called Electrical Double-Layer Capacitors, gold capacitors, and farad capacitors, store energy through polarized electrolyte. It is an electrochemical element, but no chemical reaction occurs during its energy storage. This energy storage process is reversible, and it is precisely because this super capacitor can be repeatedly charged and discharged hundreds of thousands of times. A supercapacitor can be considered as two non-reactive porous electrode plates suspended in an electrolyte. When power is applied to the electrode plates, the positive electrode plate attracts negative ions in the electrolyte, and the negative electrode plate attracts positive ions, which actually forms two capacitive storages. Layer, the separated positive ions are near the negative plate, and the negative ions are near the positive plate.
Supercapacitors can be quickly charged and discharged, and the peak current is limited only by their internal resistance, and even a short circuit is not fatal. In fact, it depends on the size of the capacitor unit. For matched loads, small units can put 10A and large units can put 1000A. Another limiting condition of the discharge rate is heat. Repeatedly discharging at a violent rate will increase the temperature of the capacitor and eventually lead to an open circuit.
The resistance of the super capacitor prevents its rapid discharge. The time constant of the super capacitor is 1-2s. It takes about 5τ to completely discharge the resistance-capacitive circuit, that is, if the short-circuit discharge takes about 5-10s (they are due to the special structure of the electrode. It actually takes several hours to fully discharge the residual charge.
Supercapacitors store energy in the separated charges. The larger the area for storing the charges, the denser the separated charges, and the larger the capacitance. The area of ​​a conventional capacitor is the flat area of ​​a conductor. In order to obtain a larger capacity, the conductor material is rolled very long, and sometimes its special structure is used to increase its surface area. Traditional capacitors use insulating materials to separate their two electrode plates, usually plastic films, paper, etc. These materials are usually required to be as thin as possible. The surface area of ​​the supercapacitor is based on a porous carbon material. The porous junction of the material allows its area to reach 2000m / g, and a larger surface area can be achieved through some measures. The distance at which supercapacitors are separated by charge is determined by the size of the electrolyte ions that are attracted to the charged electrode. This distance (<10 A) and the distance that can be achieved with traditional capacitor film materials are even smaller. This huge surface area coupled with a very small charge separation distance makes supercapacitors have a surprisingly large electrostatic capacity compared to traditional capacitors, which is also their "super".

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