Regarding its structure, a supercapacitor is identical to a normal capacitor except that its plates have a larger area and the distance between their plates is shorter. Also, regarding their energy storage mechanism, they both store energy through static electricity as compared to chemical reactions in batteries.
What makes supercapacitors different from normal capacitors is their structure that makes them capable of storing higher electrostatic energy. For example, in supercapacitors, the plates are covered with such substances as activated charcoal which gives them a bigger area for storing electrostatic energy.
Also in supercapacitors, instead of using standard dielectrics that separate capacitor plates, both plates are soaked in an electrolyte that is separated by such insulators as paper or plastic. In such a configuration, the distance between the plates and the insulator, or separator, is as low a the size of a molecule that acts as two capacitors with high a capacitance.
It this arrangement of plates and the greater efficient surface area combined with extremely small separation of plates that allows a supercapacitor to have a much higher capacitance and energy density.
This provides a supercapacitor with the unique feature of storing a large amount of energy.
Unlike a battery, there is an infinite life cycle for a supercapacitor, with little wear and tear from long-term use. Therefore, it can be charged and discharged for an infinite number of times. Supercapacitors are used in many applications because of their properties. They are widely deployed providing power and fill energy disparities. In certain applications such as battery-free devices, they are good replacements for batteries.
- Supercapacitors have significantly lower capacity than batteries, but they can be charged very fast. They can produce extremely high currents without damaging themselves, and without any complications, they can withstand a wide temperature range.
- Supercapacitors are most efficient for bridging energy differences that last from a couple of seconds to a couple of minutes and can be quickly recharged.
- Because supercapacitors work electrostatically, they can be charged and discharged several times theoretically rather than through reversible chemical reactions. They seem to have little internal resistance, which means they store and release energy without a lot of energy — and operate at approximately 100 percent capacity (typical 97–98 percent).
- Chemical reactions are the battery lifespan limiting factor. Supercapacitors are not dependent on chemical reactions to store energy, making supercapacitors ‘ lifespan much longer than batteries.
- Supercapacitors have an effective operating temperature even larger (from about -40F to + 150F).
- They do not contain a constant voltage such as batteries. As you take charge of them the voltage drops, so whatever you are going to power with them will need to tolerate this.
- Supercapacitors have a higher upfront cost than batteries, resulting in the use of batteries in many applications. Given the differences in lifespan between supercapacitors and batteries, even with the higher initial price, the long-term cost of supercapacitors can be a cheaper option. It all depends on the lifetime of the particular application needed.
- In terms of cost per watt, supercapacitors have low specific energy.
- Supercapacitors have the highest energy efficiency of any capacitor design, but batteries in this class are far inferior to any capacitor. Chemically, batteries are stored while capacitors are electrically charged. Chemical processes can store much more power than electrical storage, which leads to the more regular use of batteries in applications requiring higher storage.
- Supercapacitors aren’t well-suited for long-term energy storage. The discharge rate of supercapacitors is significantly higher than lithium-ion batteries; they can lose as much as 10-20 percent of their charge per day due to self-discharge.
- While batteries provide a near-constant voltage output until spent, the voltage output of capacitors declines linearly with their charge.
In many applications, the differences mentioned above prevent using supercapacitors in place of batteries. In some applications, there is not sufficient space to add as many supercapacitors needed to reach the energy of the intended batteries. Other applications require using supercapacitors in order to keep the charge longer or they have to be recharged more often than batteries, which is not always an option.
There has been some progress in supercapacitor technologies allowing a higher energy density; however, such a feature does not seem to be within the range of a battery’s energy density. In some applications though, a hybrid configuration proves to be the most useful.
Supercapacitors are used for applications that need a burst of energy, while batteries are used to support long-term energy needs. Supercapacitors fall somewhere between traditional electrolytic capacitors and rechargeable batteries in lifespan, energy storage, and efficient operating temperature. They effectively bridge the functional gap between these two technologies and are gaining traction as we develop new ways to use their unique combination of energy exchange and storage abilities. Pairing supercapacitors with batteries in hybrid arrays offer the possibility to get the best of both worlds. We should expect to see supercapacitors more often in the future.