What is a supercapacitor? You can think of a supercapacitor as a battery with very low internal resistance.
Charging a supercapacitor is simple, as long as its peak voltage is not exceeded. As for discharging a supercapacitor, the voltage decreases, while the current depends on the load. Generally, the resistance of the downstream load varies, not remains constant. If it were constant, the current would also decrease.
Supercapacitors, also known as electrochemical capacitors, electric double-layer capacitors, gold capacitors, or farad capacitors, are electrochemical components that store energy by polarizing electrolytes and were developed in the 1970s and 1980s.
Unlike traditional chemical power sources, supercapacitors are a type of power source with special properties, falling between traditional capacitors and batteries. They primarily rely on the electric double layer and redox pseudocapacitance to store electrical energy. However, no chemical reaction occurs during the energy storage process, making it reversible. This is why supercapacitors can be charged and discharged hundreds of thousands of times.
The specific details of a supercapacitor's structure depend on its application and usage. These materials may vary slightly depending on the manufacturer or specific application requirements. What all supercapacitors have in common is that they all contain a positive electrode, a negative electrode, and a separator between these two electrodes. An electrolyte fills the pores created by the two electrodes and the separator.
The structure of a supercapacitor, as shown in the figure, consists of porous electrode materials with high specific surface area, current collectors, a porous battery separator, and an electrolyte. The electrode materials and current collectors must be tightly connected to minimize contact resistance. The separator should possess the highest possible ionic conductivity and the lowest possible electronic conductivity; it is generally made of a fibrous electronic insulating material, such as a polypropylene membrane. The type of electrolyte is selected based on the properties of the electrode materials.
The components of a supercapacitor can vary from product to product. This is determined by the geometry of the supercapacitor package. For prismatic or square packaged products, the internal structure is based on the arrangement of internal components, where the internal collectors are extruded from a stack of electrodes. These collector pads are soldered to the terminals, thus extending the current path outside the capacitor.
For products with circular or cylindrical packages, the electrodes are cut into a roll configuration. Finally, the electrode foil is soldered to the terminals, extending the external capacitive current path.
Its basic principle is the same as other types of double-layer capacitors, which utilizes the double-layer structure composed of porous activated carbon electrodes and electrolytes to obtain ultra-large capacity.
Its outstanding advantages include high power density, short charge and discharge time, long cycle life, and wide operating temperature range. It is the largest capacity double-layer capacitor that has been put into mass production in the world.
Based on different energy storage mechanisms, they can be divided into the following two categories:
1. Electric Double Layer Capacitance: This is generated at the electrode/solution interface by the directional arrangement of electrons or ions, creating a charge opposition. In an electrode/solution system, an electric double layer forms at the interface between the electron-conducting electrode and the ion-conducting electrolyte solution. When an electric field is applied to the two electrodes, the anions and cations in the solution migrate towards the positive and negative electrodes, respectively, forming an electric double layer on the electrode surface. After the electric field is removed, the positive and negative charges on the electrodes attract the oppositely charged ions in the solution, stabilizing the electric double layer and creating a relatively stable potential difference between the positive and negative electrodes. At this point, for a given electrode, an equal amount of oppositely charged ions (dispersion layer) will be generated within a certain distance (the electrode's charge level), maintaining its electrical neutrality. When the two electrodes are connected to an external circuit, the charges on the electrodes migrate, generating a current in the external circuit. Ions in the solution migrate into the solution, becoming electrically neutral. This is the charging and discharging principle of an electric double layer capacitor.
2. Faraday pseudocapacitor: First proposed by Conway, its theoretical model involves the underpotential deposition of electroactive materials on the electrode surface and near-surface or bulk phase in a two-dimensional or quasi-two-dimensional space. This leads to highly reversible chemisorption-desorption and redox reactions, generating capacitance related to the electrode's charging potential. For Faraday pseudocapacitors, charge storage includes not only storage on the electric double layer but also redox reactions between electrolyte ions and the electrode's active materials. When ions in the electrolyte (such as H+, OH-, K+, or Li+) diffuse from the solution to the electrode/solution interface under an applied electric field, they enter the bulk phase of the active oxide on the electrode surface through redox reactions at the interface, thus storing a large amount of charge in the electrode. During discharge, these ions that entered the oxide return to the electrolyte through the reverse of the redox reactions, while the stored charge is released through the external circuit. This is the charging and discharging mechanism of the Faraday pseudocapacitor.
(1) Fast charging speed; it can reach more than 95% of its rated capacity in 10 seconds to 10 minutes.
(2) Long cycle life, with 10,000 to 500,000 deep charge-discharge cycles and no "memory effect";
(3) It has a strong high-current discharge capability, high energy conversion efficiency, low process loss, and a high-current energy cycle efficiency ≥90%;
(4) High power density, reaching 300W/KG~5000W/KG, equivalent to 5~10 times that of a battery;
(5) The product's raw material composition, production, use, storage, and dismantling processes are all pollution-free, making it an ideal green and environmentally friendly power source;
(6) The charging and discharging circuit is simple, requiring no charging circuit like that of a rechargeable battery, resulting in a high safety factor and maintenance-free long-term use;
(7) Excellent ultra-low temperature characteristics, with a wide temperature range of -40℃ to +70℃;
(8) Easy to detect; remaining battery power can be read directly.
(9) Capacity range is usually 0.1F--1000F.
Advantages of supercapacitors:
Achieving farad-level capacitance in a very small volume;
No special charging circuit or discharge control circuit is required;
Compared to batteries, overcharging and over-discharging do not negatively impact their lifespan.
From an environmental perspective, it is a type of green energy;
Supercapacitors can be soldered, thus eliminating problems such as weak connections found in batteries.
Disadvantages of supercapacitors:
Improper use may lead to electrolyte leakage and other problems.
Compared to aluminum electrolytic capacitors, it has a higher internal resistance and therefore cannot be used in AC circuits;
Company Introduction Editor
The farad, abbreviated as "F", is symbolized as F.
One farad is the voltage difference between the two plates of a capacitor when it stores one coulomb of charge; 1F = 1C/1V.
One coulomb is the amount of electricity transported by a current of 1 A in 1 second, i.e., 1 C = 1 A·S;
1 coulomb = 1 ampere-second;
1 farad = 1 ampere-second per volt;
The discharge capacity of a 12V 14Ah battery is 14 * 3600 * 1/12 = 4200 Farads (F). (Note: A 12V 14Ah battery is made up of 6 2V 14Ah batteries connected in series. If it is changed to 6 batteries connected in parallel, it becomes 2V 84Ah, which is equivalent to 168Ah per 1V). The Earth's capacitance is only about 1-2F.
