Why are supercapacitors "super"?

Why are supercapacitors "super"?

EDLC (Electrochemical Double Layer Capacitor) is an electrochemical capacitor, which is called a "super" capacitor mainly because of its high energy density. Compared with traditional electrolytic capacitors, its capacity is several orders of magnitude higher. This advantage stems from the unique structure of supercapacitors.

In traditional capacitors, charges move under force in an electric field. When there is a medium between conductors, it hinders the movement of charges and causes them to accumulate on the conductor, resulting in the accumulation and storage of charges. The amount of stored charge is called capacitance.

And supercapacitors can be simply seen as two non reactive porous electrode plates suspended in an electrolyte. When electricity is applied to the electrode plate, ions of opposite polarity in the electrolyte will form two tightly packed charge layers on both sides of the electrode plate, similar to a flat plate capacitor that produces a capacitive effect, achieving the purpose of energy storage.

The tight charge layer spacing formed on the electrode is much smaller than that of a regular capacitor, and due to the positive correlation between the energy storage capacity of the capacitor and the planar area of the electrode, porous activated carbon materials are often used on the electrode surface of supercapacitors, with an effective area tens of thousands of times that of a smooth surface. Therefore, the energy storage capacity (electrostatic capacity) of supercapacitors is much greater than that of traditional capacitors.

Supercapacitors do not have traditional dielectrics, but are separated by insulators. This insulation layer can allow positive and negative ions in the electrolyte to pass through. The electrolyte itself does not conduct electrons, so there will be no leakage inside the capacitor after charging is completed; When discharging, electrons on the electrode flow from one pole to another through an external circuit, resulting in a significant reduction in ion adsorption between the electrode and the electrolyte, and the positive and negative ions in the electrolyte are evenly distributed again.

This special architecture determines that supercapacitors have the capital to be flexible in many performance aspects compared to general capacitors and other energy storage technologies, to the extent that they are dubbed "super".

Capacitance: The most capricious performance parameter for supercapacitors is capacitance. The capacity of supercapacitors far exceeds that of traditional capacitors. The capacity of a standard battery sized electrolytic capacitor is several tens of microfarads, while the capacity of supercapacitors of the same size ranges from 0.1F to several thousand F (even tens of thousands of F), with a difference of up to five orders of magnitude.

Charging speed: The charging speed of supercapacitors is extremely fast, usually reaching 95% of the rated capacity in just a few seconds to 10 minutes, which is two to three orders of magnitude smaller than the charging time of batteries, killing the charging battery in seconds.

Ultra long lifespan: The ultra long cycle life is also one of the most capricious parameters of supercapacitors. Its charging and discharging cycles can be used hundreds of thousands of times, two orders of magnitude higher than charging batteries, and make the cost of each charging and discharging cycle much lower than batteries. Moreover, compared to secondary batteries, supercapacitors have no overcharging risk, no "memory effect", and the electrodes will not corrode.

Power density: Although the energy density of supercapacitors is less than 10% of that of batteries, their power density is very arbitrary, as high as 10 to 100 times that of batteries. Due to its strong peak current discharge capability and high energy conversion efficiency during charging and discharging.

In addition, compared with rechargeable batteries, supercapacitors have the advantages of lower cost, constant discharge voltage, simple external circuits, good low-temperature characteristics, and more environmentally friendly, making them highly favored in many energy storage applications.