What is the difference between Farad capacitors and ordinary capacitors

 What is the difference between Farad capacitors and ordinary capacitors?   

      Supercapacitors , also known as electrochemical capacitors , electric double-layer capacitors , gold capacitors , and Farad capacitors, are electrochemical components developed from the 1970s and 1980s to store energy through polarized electrolytes.

       Different from traditional chemical power sources, it is a power source with special properties between traditional capacitors and batteries. It mainly relies on electric double layers and redox pseudocapacitive charges to store electrical energy. However, there is no chemical reaction during its energy storage process. This energy storage process is reversible, and it is precisely because of this that the supercapacitor can be repeatedly charged and discharged hundreds of thousands of times.

      The specific details of the supercapacitor structure depend on the application and use of the supercapacitor. These materials may vary slightly due to manufacturer or specific application needs. Common to all supercapacitors is that they contain a positive electrode, a negative electrode, and a separator between the two electrodes, and the electrolyte fills the two pores separated by the two electrodes and the separator.

The structure of supercapacitor is composed of porous electrode material with high specific surface area, porous battery separator and electrolyte. The separator should meet the conditions of having as high ionic conductance as possible and as low electronic conductance as possible, and is generally an electronic insulating material with a fiber structure, such as a polypropylene film. The type of electrolyte is selected according to the properties of the electrode material.

According to the different energy storage mechanisms, it can be divided into the following two categories:

1. Electric double layer capacitance : It is generated by the confrontation of charges caused by the directional arrangement of electrons or ions at the electrode/solution interface. For an electrode/solution system, an electric double layer is formed at the interface of the electronically conducting electrode and the ionically conducting electrolyte solution. When an electric field is applied to the two electrodes, the anions and cations in the solution migrate to the positive and negative electrodes respectively, forming an electric double layer on the surface of the electrodes; after the electric field is removed, the positive and negative charges on the electrodes are in phase with the oppositely charged ions in the solution. The attraction makes the electric double layer stable, and a relatively stable potential difference is generated between the positive and negative electrodes. At this time, for a certain electrode, an opposite ion charge equivalent to the charge on the electrode will be generated within a certain distance (dispersion layer) to keep it electrically neutral; when the two electrodes are connected to the external circuit, the The charge migrates to generate a current in the external circuit, and the ions in the solution migrate to the solution to be electrically neutral, which is the charging and discharging principle of the electric double layer capacitor.

2. Faraday quasi-capacitance : its theoretical model was first proposed by Conway, which is that electroactive substances undergo underpotential deposition on the electrode surface and near-surface or two-dimensional or quasi-two-dimensional space in the bulk phase, and a highly reversible chemical adsorption occurs. Desorption and redox reactions result in capacitance related to electrode charging potential. For Faraday quasi-capacitors, the process of storing charges includes not only the storage on the electric double layer, but also the redox reaction between electrolyte ions and electrode active materials. When the ions in the electrolyte (such as H+, OH-, K+ or Li+) diffuse from the solution to the electrode/solution interface under the action of an applied electric field, they will enter the active oxide on the surface of the electrode through the redox reaction on the interface. in the bulk phase, so that a large amount of charge is stored in the electrode. During discharge, these ions entering the oxide will return to the electrolyte through the reverse reaction of the above redox reaction, and the stored charge will be released through the external circuit, which is the charging and discharging mechanism of the Faraday quasi-capacitor.