Supercapacitors, also known as ultracapacitors, are electrochemical capacitors and, as such, a further development of the Electric double-layer capacitor (EDLC). Compared to batteries of the same weight, supercapacitors have only about 10% of their energy density, but their power density is about ten to a hundred times greater.
Supercapacitors can therefore be charged and discharged much faster. They can also withstand many more switching cycles than accumulators and are therefore suitable as a replacement or supplement when a high switching load is required. The field of application of supercapacitors ranges from the provision of very small currents to obtain data from static storage devices (SRAM) in electronic devices to the field of power electronics, for example as storage of electrical energy in the KERS system of Formula 1 racing cars, in Citroen vehicles with e-HDI engines to support the automatic start-stop system (microhybrid) or in utility braking in vehicles such as buses and motorcycles.
In contrast to ceramic, film and electrolytic capacitors, supercaps do not have a dielectric in the conventional sense. The capacitance values of these capacitors result from the sum of two storage principles:
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- Static storage of electrical energy by charge separation in Helmholtz bilayersin a double-layer capacitance.
Electrochemical storage of electrical energy by Faraday charge exchange with the help of redox reactions in a pseudocapacitance. - Double-layer and pseudo-capacitance add up to a total capacitance in all electrochemical capacitors. However, depending on the design of the electrodes, they have a very different share of the total capacitance. For example, the pseudocapacitance of a suitable electrode can be a hundred times greater than the double-layer capacitance for the same surface area.
Double-layer and pseudo-capacitance add up to a total capacitance in all electrochemical capacitors. However, depending on the design of the electrodes, they have a very different share of the total capacitance. For example, the pseudocapacitance of a suitable electrode can be a hundred times greater than the double-layer capacitance for the same surface area.
Supercapacitors are divided into three different capacitor families, depending on the design of their electrodes:
- Double-layer capacitors have carbon electrodes or their derivatives with a very high static double-layer capacitance. The share of Faraday pseudo-capacity in the total capacity is only small.
- Pseudocapacitors have electrodes made of metal oxides or conductive polymers and have a very high proportion of Faraday pseudocapacitance.
- Hybrid capacitors have asymmetrical electrodes, one with a high double-layer capacitance, the second with a high pseudo-capacitance. Hybrid capacitors include lithium-ion capacitors.
In supercapacitors, the electrolyte is the conductive connection between two electrodes. This distinguishes them from electrolytic capacitors, where the electrolyte is the cathode and thus forms the second electrode.
As industrial products, supercapacitors are passive electronic components and bridge the gap between capacitors and accumulators. They have the highest capacitance values per component among capacitors, which are 10,000 times greater than those of electrolytic capacitors.
Supercapacitors are polarized components that must only be operated with correct polarity. The polarity of asymmetrical electrodes is determined by design, while in the case of symmetrical electrodes it is caused by a voltage application during production.
