What’s the Difference Between a Battery and a Capacitor?

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Spend a moderate amount of time learning about how electronic devices are powered and you are likely to run across discussions of both batteries and capacitors. The two devices are central to making our electronic world run. Both can be used as energy storage devices and, in fact, they are. But what is the difference between the two?

This is more than just a question of curiosity. Engineers are turning to capacitors more frequently than ever before. If they can improve capacitor technology enough, they have the possibility of reducing our dependence on batteries for powering everything from hand-held electronics to electric cars.

                   How Batteries Work

Batteries can be designed in different ways depending on the materials used and the reason for building them. For the purposes of this discussion, let us focus on rechargeable lithium-ion batteries, like the ones sold by Salt Lake City’s Pale Blue Earth. A typical consumer battery relies on three major components:

  • A cathode (a positive electrode)
  • An anode (a negative electrode)
  • An electrolyte (a substance through which ions pass).

Batteries do not store electricity. They store energy as chemicals. That energy is turned into an electric charge by a chemical process. In simple terms, ions moving from the negative side of the battery to the positive side creates the electric charge that powers the device. Thanks to their density, batteries can store a significant amount of energy and deliver it at a slow and consistent rate.

                   How Capacitors Work

Capacitors have many different uses. As energy storage devices, they work on the principle of storing protons and electrons on separate plates. The plates generally have some sort of insulating material between them.

Unlike batteries, capacitors store actual electricity. They just store it as electrostatic charges rather than electric current. It should be noted that a capacitor’s ability to store electricity is directly related to the size of its plates. The bigger the plates, the more surface area for storage.

Capacitors are sometimes preferred over batteries because they can be recharged quickly and they don’t break down over time. On the other hand, capacitors discharge relatively quickly. They do not deliver the slow and steady discharge you get from batteries.

                   How Super Capacitors Work

There is a third energy storage device many people consider a hybrid, which is to say the best of a battery combined with the best of the capacitor. Making a super capacitor starts with the same basic principles as a standard capacitor. You create two plates capable of storing opposite charges.

What makes the super capacitor so different is the electrolyte material between the plates. In a regular capacitor, the two plates are kept entirely separate. In a super capacitor, there is an electrolyte between them. This allows for passing ions back and forth – just like a battery.

A super capacitor gives you a slower, more consistent current when ions are moving through the electrolyte. But because the capacitor is still storing electrical charges in each of its plates, it retains its ability to be charged quickly. A super capacitor’s plates should last just as long as a standard capacitor.

There are plenty of practical applications here. For example, consider the electric car. What if a company like Tesla could turn an entire car body into one giant super capacitor? Perhaps there would be no need for lithium-ion batteries. For the record, scientists are working on that very concept right now.

At any rate, now you know the differences between a battery and capacitor. They are important differences to people who design and build electronic devices.

Hattie B. Trosclair

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