A supercapacitor (SC) is an electric device for storing large amounts of electric charge. It is called super (also ultra) because it can store much more energy than regular capacitors. In terms of design and performance, it is somewhere between a regular capacitor and a rechargeable battery. Supercapacitors are used, for example, in regenerative braking and start-stop systems, wind turbines, photographic flashes, and defibrillators.
How do supercapacitors work?
Like regular capacitors, a supercapacitor consists of two electrodes, a separator, and an electrolyte. When charged, the positive ions in the electrolyte form a layer on the negatively polarised electrode and the other way around forming electric double layers. This means that no physical or chemical changes occur when the charge is stored. This makes it possible to accept and deliver the charge much faster than batteries.
What differentiates supercapacitors from capacitors is the use of porous materials as electrodes which gives them a bigger surface area. The bigger the surface area, the higher the amount of charge the electrode can store. Electrodes are mostly made of different carbon-based materials such as activated carbon, graphene, and graphite. Also, the distance between the layers in a supercapacitor is much smaller than in a regular capacitor. This is because they use different techniques to separate the charges. Capacitors use a physical non-conductive material such as glass, ceramic or air as a separator. But supercapacitors separate the charge electrostatically or chemically.
Advantages and disadvantages
Supercapacitors have attracted a lot of attention due to their fast charge-discharge rates, longer life cycle, high power, and high energy density. They store more energy than regular capacitors, can charge and discharge much faster than batteries and can be recharged a large number of times with little or no degradation. While supercapacitors store less energy than batteries, they can release it much quicker, because the discharge is not dependent on a chemical reaction. They are also much safer and less toxic than batteries since they don’t overheat and don’t contain heavy metals.
Supercapacitors are mainly used in applications where a system needs to charge rapidly or deliver a burst of power, rather than for long-term energy storage. This means that in cars they are used for acceleration and in regenerative braking systems but not as the main power source. At the moment, Li-ion batteries are still a better fit for that application. But with the growing need to replace fossil-fuel cars, a lot of investments are made into research on how to improve both supercapacitors and batteries.