Knowing the fundamentals of supercapacitors is a prerequisite for comprehending the subject matter of Energy storage.
A supercapacitor is a high-capacitance capacitor that has been engineered for specific use. When an external voltage is supplied, the surface of the electrode material becomes positively and negatively charged respectively, and the presence of oppositely charged ions in the electrolyte starts accumulating on the electrode surface and forming double layers that electrostatic storage of charge leads to the concepts of Supercapacitor.
This charge storage mechanism is called EDLC (Electrical double-layer capacitance).
The EDLC-type supercapacitor is well-known for having a high power density but low energy density.
This is one of the disadvantages of its applicability for a wide range of devices. Scientists working hard to increase the energy density of supercapacitors by various techniques, The notion of pseudo-capacitance is introduced to address the issues.
Pseudo-capacitors feature a combination of charge storage mechanisms: Faradic (battery-like) and non-faradic (EDLC-like).
As a result, the device’s performance boosts energy density by 10- 20 times compared to EDLC-based supercapacitors.
What distinguishes supercapacitors from batteries?
Supercapacitors and batteries differ in several aspects. The most significant one is the electrostatic surficial charge storage mechanism which quickly stores and supplies vast amounts of energy.
That is high power density compared to batteries’ electrochemical charge storage like intercalation and deintercalation of ions, i.e. Na in sodium-ion battery and Li in Lithium-ion battery.
Because of the charge storage mechanism of batteries i.e., redox reaction and phase change process leads to slow charging and discharging.
The amount of energy storage in a supercapacitor is 5-10 times less than the batteries because of a different method of charge storage. That’s why supercapacitors have low energy density.
Another aspect is the higher cycle life of supercapacitors than batteries because they can withstand a higher number of charge-discharge cycles before significant degradation of performance, making supercapacitors more durable.
Presently, the supercapacitor field is new compared to battery, which makes it costlier, but the device’s durability makes it most cost-effective in specific applications.
The two types of devices are differentiated by their energy and power densities on the Ragone plot presented below.
Application of Supercapacitor devices in regenerative braking of EVs
A prime example is the massive surge in efforts to conserve non-renewable energy and develop other ways to create renewable energy by harnessing waste heat to do useful work.
In this regard, researchers are working on one of the technologies to extract energy from the kinetic energy when the vehicle applies the brakes.
They are successful in extracting and converting it into electrical energy.
Still, this energy conversion process is rapid, and we need some energy storage devices for that purpose battery came to mind.
Still, due to low power density battery is unable to work in this situation, but one of the devices that can work is a supercapacitor because of its high power density and extensive life cycle.
Maxwell Technologies has installed several regenerative braking devices on American light rail trains. Further applications of Supercapacitors are shown in the diagram below
What exactly is a hybrid energy storage system (HESS)?
Owing to the various energy delivery methods, researchers are developing hybrid energy storage devices that combine the high energy density of batteries with the high power density of supercapacitors; in this case, we will refer to this device as BAT-CAP.
As a result of this system, Electric cars can deal with the problem of long-distance running on a single charge and the problem of high vehicle speed, which is not successful with the earlier battery technology due to its restrictions of low power density.
When supercapacitor devices will be available on the market?
Since supercapacitor technology is new compared to battery technology, a significant research effort is being conducted in this sector to improve its materials chemistry and other crucial features.
Nowadays, several organizations manufacture supercapacitor devices, including the renowned Maxwell technology, a United States-based company that Tesla already acquired to enter this field.
Other international companies are also present in the market like Nippon Chemi-Con and Skeleton Technologies etc.
Nonetheless, India has begun to join this market, and SPEL, situated in Pune, is India’s first Supercapacitor maker. Considering all these developments, it can be estimated that supercapacitors will be commercially available within one-two decades on a significant scale.
Concluding remark
Both supercapacitors and batteries can store and provide renewable energy when needed. However, their energy requirements for electric vehicles are distinct.
The supercapacitor provides power for starting and accelerating the vehicle, whereas a battery is required for long-term operation. Both technologies have their place and can complement one another to better future outcomes, but they cannot completely replace one another.
