Understanding ultracapacitors

Ultracapacitors are also known as a supercapacitor or an electrochemical capacitor. Ultracapacitors are electrical energy storage devices that store electrical charges in large amounts. It does not lose its energy just like the ideal capacitors. Well, the simplest form of capacitor has two parallel conducting metal plates that are separated by an insulating material like air, mica, paper ceramic, etc. all these are called dielectric through a distance “d”.

Today you’ll get to know the definition, applications, diagram, working, specifications, characteristics, construction, properties, types, and technology behind ultracapacitors. You’ll also get to know the advantages and disadvantages of the device.

Read more: Understanding capacitor

What is an ultracapacitor?

Ultracapacitor which is also known as a supercapacitor is an electrical device that stores charge in large amounts. It is called ultra because it has a higher capacitance value than regular capacitors. These capacitors have low voltage limits and they have become a better choice over the common capacitors. This is because they offer higher power density, consume less power, and are safe and easy to operate.

An ultracapacitor operates between the limit of an ordinary capacitor and a battery. Although, the device has just begun to gain population in the industry. They are suitable for applications from efficient large-scale energy storage to a very small portable devices. This is because of their energy density, short charging cycle, and wide range of operating temperatures.

Finally, ultracapacitors are defined as electronic devices that are used to store extremely large amounts of electric charge. They are known as double-layer capacitors and in few years to come, supercapacitors will replace or augment battery and fuel cell systems in many areas of technology.

Read more: Understanding capacitance in AC circuits

Applications of ultracapacitors

Ultracapacitors have the following applications”

• Wind turbines
• Electric cars
• Photographic flash
• Flywheel in machines
• Static memories (SRAM)
• Regenerative braking in the automotive industry
• Mp3 players
• Industries electrical motors.

Also, supercapacitors can be used for the following:

• Storage of energy in KERS, or dynamic braking systems (Kinetic Energy Recovery System) in the automotive sector.
• Supercapacitors can be used in an electrical generator that can convert kinetic energy to electric energy and store it in the device itself. This energy can be reuse to provide power for acceleration.
• The device can also be employed where a high capacitor is not required, but a high cycle or quick recharging is necessary.
• Ultracapacitors are going to be excellent application in cell phones, laptops, electric cars, and all other devices that uses batteries.

Read more: Understanding the charge in a capacitor

Characteristics

Supercapacitors have three main characteristics which include charge time, specific power, and cycle life, and safety.

Charge time:

Unlike the ordinary capacitor, ultracapacitors have charge and discharge times. This means it is possible to achieve high charge and discharge currents due to low internal resistance. This is having an advantage over batteries because it usually takes several hours to reach a fully charged state. Let take a cell phone battery as an example, it will take supercapacitors just two minutes to have the same charge.

Specific power:

Ultracapacitors have a specific power 5 – 10 times greater than batteries. The specific power in both a battery or supercapacitor is a measure used to compare different technologies in terms of maximum power output divided by the total mass of the device. Let take for instance, Li-ion batteries have a specific power of 1-3 kW/kg, it is around 10 kW/kg for supercapacitors. This is the device is suitable for applications that require quick bursts of energy to be released from the storage device. Finally,

Cycle life and safety:

When compared with batteries, supercapacitors are much safer. This is because batteries are known to explode due to excessive heating when circuited, whereas supercapacitors do not overheat due to their low internal resistance. However, shorting a fully charged supercapacitor will result in electrical arcing, and might damage the device. Well, it’s a turn up to batteries since they generate heat have no business with the device.

Read more: Understanding the dielectric of a capacitor

Diagram of ultracapacitors:

Specifications of ultracapacitors

The following are the specifications of ultracapacitors:

• The device has a high capacitance of about 2 kF.
• Supercapacitors bridge the gap between conventional capacitors and rechargeable batteries.
• They are capable of storing large amounts of energy.
• Supercapacitors can store electricity through either electrostatic charge absorption/desorption.
• The charge time of the device is about 1-10 seconds.

Read more: Understanding the types of capacitors

Construction and properties of ultracapacitors

Just like that of electrolytic capacitors, the construction of ultracapacitors is much related. They also consist of two foil electrodes, an electrolyte, and a foil separator. The separator is sandwiched between the electrodes and the foil is folded into a shape, usually rectangular or cylindrical. It is then placed into housing, which is filled up with electrolytes and hermetically sealed. The electrolytes used here are much different from that of ordinary electrolytic capacitors.

In supercapacitors, porous materials are used as separators in order to store electric charge. it stores irons in those pores at an atomic level. Activated charcoal is the most commonly used material in modern ultracapacitors. Carbon cannot serve as a better insulator because it results in a maximum operating voltage limited below 3 V. Also, activated charcoal is not a perfect material because the charge carriers are comparable in size to the pores material and some of them cannot fit into the smaller pores. This results in a reduced storage capacity.

However, one of the most interesting materials used in ultracapacitor research is graphene. It is a substance that consists of pure carbon, arranged in a planer sheet only one atom thick. The energy densities achieve using graphene in ultracapacitors are comparable to energy densities found in batteries.

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Types of ultracapacitors

The various types of supercapacitors include electrostatic double-layer capacitors, pseudo-capacitors, and Hybrid capacitors.

Electrostatic double-layer capacitors:

These types of supercapacitors consist of two electrodes, a separator, and an electrolyte. The electrolyte is the mixture that forms positive and negative ions that dissolved in water. The separator is used to separate the two electrodes. Also, carbon electrodes or derivatives with much higher electrostatic double-layer capacitance. The separation of the charge in these types of supercapacitors is less than a conventional capacitor, ranging from 0.3 to 0.8 nm.

Read more: Understanding parallel capacitors

Pseudo capacitors:

Pseudo capacitors are also known as electrochemical pseudo-capacitors. They make use of metal oxide or conducting polymer electrodes with a high amount of electrochemical pseudo-capacitance. These types of supercapacitors store electrical energy by electron charge transfer between electrode and electrolyte. This can be achieved by a reduction-oxidation reaction which is known as a redox reaction. Finally,

Hybrid capacitors:

These types of supercapacitors are developed using the techniques of double-layer capacitors and pseudocapacitors. The electrodes used are of different characteristics. One electrode with the capacity to display electrostatic capacitance, and the other electrode with electrochemical capacitance. A good example of hybrid capacitors is the lithium-ion capacitor.

Working principle

The working of the ultracapacitor is less complex and can be easily understood. Just like a battery, a single ultracapacitor cell consists of a positive and negative electrode which is separated by an electrolyte. But, in the case of ultracapacitors, the energy is stored electrostatically, like the normal capacitor and not chemically like a battery. There is a dielectric separator separating the electrolyte like a capacitor.

The small demarcation between the electrodes allowed by the structure results in a much higher energy storage density than that of normal capacitors. However, supercapacitors store less energy than an equivalently sized battery and they can release their energy much faster. Therefore, the discharge is not dependent on a chemical reaction.

Read more: Understanding Capacitors in Series

Watch the video below to learn more on the working of an ultracapacitor:

Advantages and disadvantages of ultracapacitors

Advantages:

Below are the benefits of ultracapacitors in their various applications:

• High specific power
• Safety in Operation
• Long Lifetime
• Wide temperature range
• Maintenance-free operation
• Environmentally friendly

Read more: Understanding voltage rating of a capacitor

Disadvantages:

Despite the good benefits of an ultracapacitor, some limitations still occur. Below are the disadvantages of supercapacitors in their various applications.

• A relatively low specific energy
• Linear discharge voltage. that is, if a battery rated at 2.7V, at 50% charge it would still output a voltage close to 2.7V. on a supercapacitor, a 2.7V at 50% would output exactly half of its maximum charge voltage which is 1.35V. in another word, the output voltage of this device will fall below the minimum operating voltage of the device.
• The cost of supercapacitors is relatively high. In fact, the cost per Wh of a supercapacitor is more than 20times higher than that of Li-ion batteries.

Read more: Understanding an automotive relay

Conclusion

Supercapacitors are specially designed capacitors with very high capacitance. They combine the properties of capacitors and batteries into one device. That is all for this article, where the definition, applications, diagram, working, specifications, characteristics, construction, properties, types, and technology behind ultracapacitors are being discussed.

I hope you gained a lot from the reading, if so, kindly share with other students. Thanks for reading, see you next time!