Energy Storage Supercapacitor: Workings and applications
Supercapacitors—also known as ultracapacitors—are specifically designed capacitors capable of storing a large electrical charge.
Supercapacitors bridge the gap between electrolytic capacitors and rechargeable batteries, typically able to store 10 to 100 times more energy per unit volume or mass than electrolytic supercapacitors.
Supercapacitors offer operational voltages in the range of 1V and 3V for both organic and aqueous electrolytes and hold great promise for rapid charging and energy storage. They are also known for their virtually limitless charge cycles in contrast to lithium-ion batteries, which degrade with each passing cycle.
How supercapacitors work
Before looking at the workings of a supercapacitor, it is important to look at the workings of a typical capacitor.
Your typical capacitor is made from two metallic plates (electrodes) that separate a dielectric substance between them. When voltage is applied, electrons gather at one of the electrodes, thereby storing the electrical charge. Meanwhile, the dielectric material that is sandwiched between the two electrodes undergoes a process called dielectric polarisation that helps to increase the capacitance—the ability of a system to store an electric charge.
A supercapacitor works on the same principles except that in the supercapacitor, the wedging material is an electrolytic solution rather than a dielectric substance. When voltage is applied to a supercapacitor, an “electric double layer” is created, which aligns both positive and negative charges along the boundaries of the electrodes and the electrolytic solution. This area acts as a place of storage for electrical charge. To expand the boundaries of these areas, activated carbon is used because it is porous and has many holes in its surface that help cover a large surface area.
Supercapacitors vs. batteries
Although supercapacitors sound very similar to conventional batteries—indeed, they share the same structure due to the electrolytic solution and electrodes—there is one big difference.
In a battery, chemical reactions take place between the electrolytic solution and the electrodes. In contrast, supercapacitors only allow electron movement between electrodes. This difference means that there are various different properties between a battery and a supercapacitor, and both have their own applications.
Furthermore, batteries are widely used with a specific volume and weight, and also have better energy density. In contrast, supercapacitors are high-capacity capacitors with high power density. When compared to a battery, a supercapacitor has a fast charge-discharge capacity, can handle low-high temperature, features low impedance, and is highly reliable.
As a means to bridge the gap between capacitors and batteries, supercapacitors can be used in a large variety of applications. They can primarily be found in applications that require rapid charge and discharge cycles, such as in automobiles where they are used for regenerative braking, rather than in applications that require long-term compact energy storage like smartphones and consumer-grade devices. Smaller supercapacitor units are used as a backup power system for static random-access memory (SRAM). However, there are some consumer-grade applications that use supercapacitors because characteristics like quick recharge or prolonged life cycle are required. Examples of these include MP3 players and the flash for a professional-grade camera.
Another common application for supercapacitors is in wind turbines. Here, very large supercapacitors help to smooth out the intermittent power supplied by the wind.