What is an ultra-small electrolytic capacitor? How does it differ from a conventional capacitor?
Release time:
2022-06-27
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Ultra-small electrolytic capacitors—also known as electrochemical capacitors, double-layer capacitors, gold capacitors, or farad capacitors—are electrochemical components that have been developed since the 1970s and 1980s. They store energy by polarizing an electrolyte.
Ultra-small electrolytic capacitor Also known as electrochemical capacitors, double-layer capacitors, gold capacitors, or farad capacitors, these electrochemical components have been developed since the 1970s and 1980s. They store energy by polarizing an electrolyte.
Unlike conventional chemical power sources, this device is a special type of power source that lies somewhere between traditional capacitors and batteries. It primarily stores electrical energy by relying on charge storage via positive electrode layers and redox pseudocapacitance. However, no chemical reactions occur during the energy-storage process. This energy-storage process is reversible, allowing the capacitor to be repeatedly charged hundreds of thousands of times.
Ultra-small electrolytic capacitor The specific details of the structure depend on the capacitor’s application and usage. Due to manufacturer specifications or particular application requirements, these materials may vary slightly. What all capacitors have in common is that they include an anode, a cathode, and a separator between the two electrodes. The electrolyte fills the two pores separated by the two electrodes and the separator.
Ultra-small electrolytic capacitor The structure consists of a high-surface-area porous electrode material, a porous battery separator, and an electrolyte. The ultra-small electrolytic capacitor separator must meet conditions of the highest possible ionic conductivity and the lowest possible electronic conductivity. Typically, it is an electron-insulating material with a fibrous structure, such as polypropylene film. The type of electrolyte is selected based on the properties of the electrode material.
According to the energy storage mechanism, they can be classified into the following two categories:
1. Double-layer capacitance: At the electrode/solution interface, the oriented arrangement of electrons or ions gives rise to a charge separation. In an electrode/solution system, a double layer is formed at the interface between the electron-conducting electrode and the ion-conducting electrolyte solution.
After an electric field is applied to two electrodes, the cations and anions in the solution migrate toward the positive and negative electrodes, respectively, forming a double layer at the electrode surfaces. Once the electric field is removed, the positive and negative charges on the electrodes attract the oppositely charged ions in the solution, stabilizing the positive charge layer and creating a relatively stable potential difference between the anode and cathode.
At this point, in the case of an electrode, within a certain distance (the diffuse layer), an equal amount of oppositely charged ions is generated, matching the charge on the electrode itself, thereby maintaining electrical neutrality. If the anode is connected to an external circuit, as the electrode's charge moves, a current will flow through the external circuit, and ions in the solution will migrate into the solution, restoring electrical neutrality. This is the charging and discharging principle of a double-layer capacitor.
2. Faraday pseudocapacitance: Its theoretical model was first proposed by Conway. In a two-dimensional or quasi-two-dimensional space located at and near the electrode surface or within the bulk material, electroactive substances undergo low-potential deposition, accompanied by highly reversible chemical adsorption-desorption and redox reactions, thereby generating capacitance that is dependent on the electrode charging potential.
For Faraday pseudocapacitors, the process of charge storage involves not only the storage in the electrical double layer but also redox reactions between electrolyte ions and the electrode active materials.
When ions (such as H⁺, OH⁻, K⁺, or Li⁺) in the electrolyte diffuse from the solution to the electrode/electrolyte interface under the influence of an external electric field, they undergo redox reactions at the interface and enter the bulk phase of the active oxide on the electrode surface, thereby storing a large amount of charge on the electrode. During discharge, the ions that have entered the oxide return to the electrolyte via the reverse of the aforementioned redox reactions, and the stored charge is released through the external circuit. This is the charging and discharging mechanism of a Faraday pseudocapacitor.
Keywords:
Ultra-small electrolytic capacitor
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