Supercapacitors (also known as Ultracapacitors) have always raised a lot of attention and interest since its inception. This is due to the remarkably high capacitance and almost limitless lifecycle of charge and discharge. This post will discuss about What is Supercapacitor (Ultracapacitor), its characteristics, how it works, types, applications, advantages and disadvantages.
What is Supercapacitor (Ultracapacitor)
Supercapacitor (Ultracapacitor) is a specifically designed capacitor capable of storing enormous amount of electrical charge. Supercapacitors offer operational voltages that range between 1V and 3V for both aqueous and organic electrolytes. It also promises great potential for rapid charging and energy storage.
Unlike other capacitors that use the conventional dielectric, these supercapacitors employ two methods for the storage of electrical energy i.e. Pseudocapacitance and double layered capacitance.
Fig. 1 – Supercapacitor (Ultracapacitor) at a Glance
Pseudocapacitance is originally electrochemical, while double layered capacitance is electrostatic. Very high capacitances like 12000F can be achieved using this supercapacitor technology.
Characteristics of Supercapacitors (Ultracapacitors)
Below are some of the characteristics of Supercapacitors (Ultracapacitors).
1. Charge Time of Supercapacitor (Ultracapacitor)
The charge and discharge time of a supercapacitor or ultracapacitor can be compared to that of any ordinary capacitor. However, high charging and discharging currents can be achieved due to the minimal internal resistance offered by the supercapacitor.
While batteries generally take a long time to be fully charged, supercapacitors can be charged to the same state in under two minutes.
2. Specific Power of Supercapacitor (Ultracapacitor)
The specific power of a supercapacitor or ultracapacitor measures the highest output power divided by its total mass. Supercapacitors’ specific power is known to be 10 times the specific power of batteries. This property comes handy in applications where quick energy bursts are required to be freed from storage device.
3. Safety and Life Cycle of Supercapacitor (Ultracapacitor)
Supercapacitor is known for its high safety standards. While batteries explode because of excessive heating, supercapacitors are relatively cool due to their low resistance. They also offer a virtually limitless cycle life. This property is useful in cases where energy release and storage is carried out very frequently.
How Supercapacitor (Ultracapacitor) Works
Let’s first take a look at the working of a typical capacitor. Standard capacitors are made of two metallic plates or electrodes that separate a dielectric substance between them. Upon the application of voltage, electrons accumulate at one of the electrodes, thereby storing the electrical charge.
Meanwhile, the dielectric material that is wedged between the electrodes undergoes a process called “dielectric polarization” and helps to increase the capacitance.
Fig. 2 – Structure of a traditional capacitor
Supercapacitor also work on the same principle except that the wedging material is an electrolytic solution rather than a dielectric substance. Upon voltage application, an “electrical double layer” will be created that aligns both negative and positive charges along the boundaries of electrodes and the electrolytic solution.
This place acts as a warehouse for storing electric charges. Activated carbon is often used to expand the boundary areas. This is because, the supercapacitor’s capacitance is in direct proportion to the area of “electrical double layer”. This activated carbon is a known porous material and has many surface holes that help in covering a big surface area.
Fig. 3 – Working of a Supercapacitor (Ultracapacitor)
Due to the electrolytic solution and electrodes, supercapacitors share the structure of a typical battery for electricity storage. While chemical reactions take place between the electrolytic solution and the electrodes in a battery, supercapacitors allow only electrons movement between electrodes. These differences result in varying properties between a battery and supercapacitor.
Types of Supercapacitor (Ultracapacitor)
As earlier mentioned, Supercapacitors make use of two basic principles for energy storage i.e. electrochemical pseudocapacitance and static double layered capacitance. Based on this, supercapacitors are categorized into three different types. They are:
- Double Layered Capacitors
- Hybrid Capacitors
Double Layered Capacitors
In Double Layered Capacitors, Storage of electrical energy is achieved by charge separation in Helmholtz double layer. This acts as a boundary between the conductor electrode and electrolyte.
The electrodes are made from activated carbon or with derivatives that have greater electrostatic double layered capacitance than an electrochemical pseudocapacitance.
They have polymer conducting electrodes or transistion metal oxides that possess large electrochemical pseudocapacitance.
Storage of electrical energy is an electrochemical process and is achieved through redox reactions, intercalation on electrode surface by ions that are specifically absorbed.
Here, the electrodes are asymmetric where one of the electrodes exhibit electrostatic property while the other exhibits electrochemical capacitance. Because both Pseudocapacitance and Double-Layered capacitance make inseparable contributions to the full capacitance of an electrochemical capacitor, the concept of Supercabattery and Supercapattery have been proposed. This helps in giving clarity on hybrid devices that act both like a battery and a supercapacitor.
Applications of Supercapacitors (Ultracapacitors)
Since supercapacitors are bridging the gap between capacitors and batteries, they are being used in large number of applications. One such interesting application is the energy storage in Dynamic Breaking System or the KERS (Kinetic Energy Recovery System).
The automotive industry is making use of this approach by using electrical generators that change kinetic energy into electrical energy. This electrical energy is stored in supercapacitors and is later used to supply power required for acceleration.
Low powered applications where quick recharge or high life cycle is important , make use of the supercapacitor technology. MP3 players, photographic flash, static memories are a few such applications.
Future of Supercapacitors (Ultracapacitors)
The future of supercapacitor (Ultracapacitor) is bright and promising. Prominent among them is the plan to combine double-layered interface with existing technologies for energy storage. Addition of electrochemical capacitor to applications that run on fuel-cell has caused great improvements in performance of charge and discharge life cycles.
This is particularly seen in electric vehicle and hybrid applications. Several cities that have their public transit system running on hybrid technologies have seen improvements in charge cycles and energy storage mechanisms.
Such rapid charging and energy storage facilities are already entering the market and have caused a phenomenal shift in our thinking on storage capabilities. Supercapacitors are also envisioned to be used in laptops, cell phones, electric cars and other devices that utilize batteries.
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