What Is a Capacitor?
Before we get to supercapacitors, it’s worth quickly explaining what a regular capacitor is to help demonstrate what makes supercapacitors special. If you’ve ever looked at a computer motherboard or virtually any circuit board, you’ll have seen these electronic components.
A capacitor stores electricity as a static electric field. This is the same thing that happens when you walk across a carpet in socks and build up an electric charge, only to discharge it when you touch a door handle. You were acting as a capacitor!
Inside a typical capacitor, you’ll find two conductors separated by an insulating material. Positive charge accumulates on one conductor and negative charge on the other. Thus, there’s an electrostatic field between the two plates. There are many different ways to design a capacitor, but they all have the basic components of two charge plates and an insulator (dielectric). The insulator can be air, ceramic, glass, plastic film. liquid, or anything else that’s bad at conducting electricity.
Capacitors have many uses in electronics. In computers and other digital systems, they make sure that information isn’t lost if there’s a momentary loss of power. They also act as filters to clean up electrical surges that might otherwise damage sensitive electronics.
How Capacitors and Batteries Differ
Capacitors and batteries are similar in the sense that they can both store electrical power and then release it when needed. The big difference is that capacitors store power as an electrostatic field, while batteries use a chemical reaction to store and later release power.
Inside a battery are two terminals (the anode and the cathode) with an electrolyte between them. An electrolyte is a substance (usually a liquid) that contained ions. Ions are atoms or molecules with an electrical charge.
There’s also a separator within the electrolyte that only allows ions to pass through it. When you charge the battery, ions move from one side of the separator to the other. When you discharge the battery the opposite happens. The movement of ions chemically stores electricity or turns that stored chemical energy back into an electric current.
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Capacitor vs. Supercapacitor
Supercapacitors are also known as ultracapacitors or double-layer capacitors. The key difference between supercapacitors and regular capacitors is capacitance. That just means that supercapacitors can store a much larger electric field than regular capacitors.
In this diagram, you can see another major difference when it comes to supercapacitors. Like a battery (and unlike a traditional capacitor) a supercapacitor has an electrolyte. This means that it uses both electrostatic and electrochemical storage principles to hold an electric charge.
This is a gross oversimplification, and the really technical aspects of this would take much longer to explain. The most important thing to know about supercapacitors is that they offer the same general characteristics as capacitors, but can provide many times the energy storage and energy delivery of the classic design.
The Pros and Cons of Supercapacitors
Supercapacitors offer many advantages over, for example, lithium-ion batteries. Supercapacitors can charge up much more quickly than batteries. The electrochemical process creates heat and so charging has to happen at a safe rate to prevent catastrophic battery failure. Supercapacitors can also deliver their stored power much more quickly than an electrochemical battery, for the same reason. If the battery discharges too quickly it can also lead to catastrophic failure.
Supercapacitors are also far more durable than batteries, in particular lithium-ion batteries. While the batteries you find in phones, laptops, and electric cars start to wear out after a few hundred charge cycles, supercapacitors can be charged and emptied in excess of a million times with no degradation. The same goes for voltage delivery. A 12V battery might only provide 11.4V in a few years, but a supercapacitor will provide the same voltage after more than a decade of use.
The biggest drawback compared to lithium-ion batteries is that supercapacitors can’t discharge their stored power as slowly as a lithium-ion battery, which makes it unsuitable for applications where a device has to go long periods of time without charging.
So, as things stand at the time of writing, supercapacitors aren’t a drop-in replacement for lithium-ion batteries or other battery technologies, but there are a growing number of jobs that supercapacitors are perfect for.
Supercapacitor Products
You’ve probably used products that contain supercapacitors and didn’t even know it. The first supercapacitors were created in the 1950s by a General Electric engineer named Howard Becker. In 1978, NEC coined the name “supercapacitor” and used the device as a form of backup power for computer memory.
Today you’ll find them in laptops, GPS units, handheld computers, camera flashes, and many other electronics devices. The Coleman FlashCell used a supercapacitor instead of a battery. This meant it ran half as long as a traditional battery-powered model, but charged up in 90 seconds instead of hours.
Similarly, the S-Pen in the Samsung Galaxy Note 9 used a supercapacitor to power the wireless functions of the stylus. The power would run out in a few minutes of heavy use or after 30s seconds of stand time, but it only takes 40 seconds to fill it up again.
Supercapacitors are finding a home in the world of hybrid and electric vehicles as well. They are perfect for capturing and releasing the power from regenerative braking, which is a dynamic short-term load. Vehicles such as public transport buses or trams are also suitable for supercapacitors. They only need enough power to get to the next stop, where they’ll charge up again in seconds or minutes. Since supercapacitors don’t really wear down, this fixed public transport cycle makes a lot of sense for the technology.
Are Supercapacitors the Future of Energy Storage?
With the way research on supercapacitors is going, it seems likely that one day we’ll have supercapacitor batteries. These would be devices that have the durability and speed of supercapacitors, but with the energy density and long operational time of batteries. In 2016, scientists from the University of Central Florida created a prototype flexible supercapacitor with a higher energy density than current supercapacitors and a 30,000 charge cycle without degradation.
New materials on the nanoscale and experiments with graphene all point towards the possibility that supercapacitors with much higher energy densities are possible. Even if they don’t ever match lithium-ion batteries, a usable amount of charge, coupled with rapid recharge time could put them places where batteries currently fill a role.
Then again, there are other technologies in competition with supercapacitors. The most important of which is the fabled solid-state battery and recently graphene-infused traditional lithium-ion batteries have shown promise as well. Whichever fast-charging, durable, energy-dense technology wins the race, we’ll all be winners.
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