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Introduction to Supercapacitors

Though most common, chemical batteries are not the only way to store energy. Another device that is constantly being researched and improved is the supercapacitor. The supercapacitor stores electricity as static rather than chemical energy. While they can’t match up to batteries in energy capacity, they do have clear advantages that secure them a place in our energy-efficient future.

 How does a supercapacitor work

A supercapacitor is made up of two metal electrode plates separated by a thin and porous insulator usually made from carbon, paper or plastic that has been soaked in an electrolyte.

When a charge is applied, ions in the electrolyte migrate toward the plate with the opposite polarity. An electrical field is created by this movement, and energy is stored in the intense electric field between the ions and electrodes that keeps them together. During discharge, electrons move toward the circuit load, releasing the ions from the plate.

What is the difference between supercapacitors and batteries?

While both store energy, the supercapacitor and battery are extremely different. The energy density of the supercapacitor is only around 1 to 30 Wh/kg, compared to the 100 to 265 Wh/kg of modern lithium ion batteries. 

Conversely, the supercapacitor greatly surpasses batteries in power density. Because it does not rely on chemical reactions to release energy, the supercapacitor can release a large amount of energy in a short amount of time. The specific power of a supercapacitor can be up to 10,000 W/kg, while that of general lithium-ion batteries is around 1,000 to 3,000 W/kg.

This also means it can charge very quickly. The average charging time of a supercapacitor is 1-10 seconds, whereas batteries would need to charge for 10 minutes to up to an hour to reach full charge. 

Supercapacitors have a much longer cycle life because the materials do not degrade through the energy release process. In batteries, the chemical reactions would eventually wear down the materials and cause loss of capacity. 

Supercapacitor Applications

Despite all these advantages over batteries, the one thing that greatly holds back supercapacitors are their energy capacity. Nonetheless, they are well suited to high power applications that need to charge and discharge quickly without the need for long-term storage. 

Some small devices that make use of supercapacitors include flashes for cameras and small electrical tools. Because these devices do not need a constant flow of electricity but rather quick bursts of energy, the supercapacitor is perfect in these instances.

Though not energy dense, supercapacitors are used in certain types of electric transportation. In China, some of their electric buses in Shanghai run on supercapacitors, charging up at stops while passengers alight and board. Because they can charge in seconds, buses can keep running for the whole day without worry of running out of charge. Certain trams and light-rails in various places across Europe also make use of the same principle. 

In electric vehicles, supercapacitors can be used in regenerative braking systems, quickly absorbing and releasing energy. In this way, the supercapacitor would support the battery in powering the car, especially during acceleration where a quick burst of power would be needed.

In grid applications, another important area in the future of energy storage, supercapacitors can also be paired with batteries to bridge power gaps when there is a sudden surge of demand for energy. The supercapacitor would act as a buffer between the grid and load, quickly releasing energy when there is a sudden surge of demand so as to limit disruption of the energy flow, as well as the strain on the grid.

Testing supercapacitors

Because of supercapacitors’ many advantages, exploring ways they can play a role in energy storage is an important part of the conversation. Arbin has high quality supercapacitor testing equipment for research and development purposes. Like all of our other equipment, the supercapacitor test systems support real-world simulation charge/discharge cycles. Available for cell, module and pack testing up to 800v.

Power Tools: What’s the difference between power and energy?

When it comes to batteries, often times energy and power density are thought to be one and the same - a battery with high energy density would be a powerful battery as well. In fact, energy density and power density are very different things. Energy density relates to the amount of energy that can be stored per battery unit whereas power density relates to the maximum amount of energy that can be discharged per battery unit. Although energy density is the more commonly used measurement to determine battery performance, power density is still an important metric to consider when talking about energy systems. Understanding the relationship between these two things is essential as it helps in determining what type of battery is necessary for different products. 

Energy Density vs Power Density

*https://www.tecategroup.com/products/ultracapacitors/ultracapacitor-FAQ.php

Essentially, the main difference between energy density and power density is that batteries with a higher energy density will be able to store larger amounts of energy, while batteries with a higher power density will be able to release higher amounts of energy a lot quicker. Depending on the type of tool being energized, varying degrees of energy density and power density will be required. Take a mobile phone, for instance, phones do not need enormous amounts of energy to stay functional, instead, they need energy to be discharged consistently over extended periods of time. This means they mainly need batteries with a high energy density. On the other hand, power tools such as jigsaws and circular saws, need batteries that can release a lot of energy in one go but at the same time require the battery to have a big gas tank, which means that batteries used to energize power tools need be high in both energy and power density. 

When testing batteries of power tools, they cannot be evaluated through the same means as phone batteries, as the nature of how these products are used are completely different. Phones are used at a relatively consistent rate and thus go through relatively consistent charge and discharge cycles: Your phone is left on and used throughout the day, it is then charged at night and the cycle is repeated again day after day. Power tools on the other hand, are often not used in regular patterns like phones are and instead are used in short bursts of high power output, making their discharge cycles a lot more sporadic and unpredictable. Thus, where phones can be tested through traditional battery cycling methods which track constant current and constant voltage charge and discharge profiles, a more dynamic system must be adopted when testing batteries for power tools which take into account the many variables that may come into play when testing these types of products. 

Dynamic Cycling

Other technologies also have more dynamic discharge cycles; batteries for electric vehicles is one such example. Test equipment, like Arbin’s, should be able to test irregular charge and discharge cycles. This allows power tools or EV batteries to be tested in real life scenarios. Arbin’s equipment is guaranteed to give accurate and true to life simulations no matter the type of product that is being tested. Using true bipolar circuitry, our test systems feature cross-zero linearity and zero switching time between charge and discharge which is crucial in being able to test batteries more dynamically and precisely. 

Looking at what dynamic cycles would mean for EVs, EV drive cycles have instantaneous transitions between accelerating up a hill, to regenerative braking when going down; braking at a stoplight that slightly generates battery charge to accelerating when it turns green, requiring a lot of power. 

Likewise, power tools must run at a constant rate, like a drill spinning, but then suddenly be able to continue when faced with resistance --  like when pressed into concrete or a dense wood to drill a hole. This discharge profile has large, but relatively brief periods of high power output and still needs to last several hours of this type of repeated operation.

With over 90 pre-defined meta variables and a dozen custom ones available to users, our testing systems can be fully defined and customized to provide as accurate simulations of battery usage as possible. Arbin’s “Simulation” software feature also provides an intuitive interface which allows you to directly upload your data profile into the program to simulate without any additional programming needed. 

Conclusion

The performance of a power tool is just as good as the battery it holds, therefore it is crucial that power tools are fitted with batteries that can provide the necessary performance according to the given function the tool is meant to fulfill. At Arbin, not only are we able to provide a battery testing system that is consistently accurate, our systems are the most responsive to simulating very dynamic battery life cycles, which is key to properly re-producing the unique real-world test profiles of power tools, electric vehicles, and other applications that need more that constant current.