Most of us became familiar with what batteries do when we were just small children with all our battery-operated toys. But the history of its invention is packed with drama and uncertainty.
Artifacts were discovered outside of Baghdad that resemble batteries. They consisted of a terracotta pot with a copper cylinder and an iron rod held in place with an insulator. Some believe if they were filled with fruit juices, they would produce a small current. The most intriguing part of the story is that it pre-dates the official invention of the battery by at least 1500 years. Currently, there’s no definitive way to determine what these were really used for.
In the late 1700s, Luigi Galvani, a professor of anatomy, was performing experiments on frogs, trying to prove their testicles were in their legs. He made the observation that their legs would twitch when touched by a statically charged scalpel. He spent the next ten years performing experiments, and found that touching unlike metals simultaneously across the legs would cause them to twitch. He concluded that there were three types electricity: friction, lightning, and his newly discovered animal electricities.
But not everyone agreed with them. Alessandro Volta, a professor of physics, a self-proclaimed genius, and a ladies’ man was convinced there was only one type of electricity. I want the frog legs. He started his own experiments, and quickly discovered that frog tissue was not the source of electricity, but a sensitive detector. He found that he could use salt water-soaked felt in place with the frog tissue and still produce electricity.
He believe that he discovered an unlimited source of electricity that came from the tension of two dissimilar metals, and the corrosion of the salt water was only an annoyance. Because of this belief, his primitive batteries, or voltaic piles, have extra plates on the top and bottom.
We now know that the current is generated by a process of oxidation and reduction. Oxidation occurs at the more reactive electrode, and reduction happens at the less reactive electrode. The electrode that’s being oxidized will be consumed, and positive ions will diffuse away from it. Depending on the chemistry of the cell, at the reduction electrodes, sometimes gas is formed, and other times, it’s plated, and negative ions diffuse away. Externally in the circuit, the electrons flow from the oxidation electrode to the reduction electrode.
This is the electrical symbol for a battery. The small line is the negative terminal. See the resemblance?
This is a partial list of the activity series of metals, lithium being the most active, and gold being the least. The more active a metal, the more likely it will lose electrons and oxidize. To the right, you can see the standard oxidation potential in volts. In a perfect world, you can use these numbers to calculate out the voltage of your cell, depending on the electrodes you choose. If we chose zinc and copper, the difference would be about one volt.
You can create your own voltaic cell at home very easily with two dissimilar pieces of metal and a piece of paper soaked in vinegar. The bottom plate is a piece of copper. I’m not exactly sure what the washer is made of. When I test with the volt meter, I can see that it’s 0.8 volts.
We can tell that the washer is the anode, because the volt meter will indicate with a negative sign if the leads are hooked up backwards. Cells like this have a disadvantage, because they continue to react, even when current isn’t flowing.
An improved cell would have electrodes surrounded by a solution that only reacts when current is flowing. This can be achieved by using a salt bridge with a permeable membrane that allows ions to pass. Rechargeable batteries are very similar to one time use batteries. The difference is, the chemistry can be reversed, restoring the electolytes and the electrodes.
Lead acid is an example of this type of battery. During discharge, the electrodes are turned from lead and lead oxide to lead sulfate, and during charging, it’s returned back to lead and lead oxide and sulfuric acid.
You can increase the voltage of a battery by adding more cells stacked in series. I’ll demonstrate this by hooking 40 9-volt batteries together.
Oops. I’d better get some bigger electrodes.
If you need to increase current, you can put batteries in parallel. This is effectively making their plates a larger surface area.
Here I’m shorting a fine wire across the leads of the 9-volt battery. Not much happening. Now we see smoke when I hook two batteries in parallel, and short the lead. And with three batteries, it’s far too much current for such a small wire, and it immediately melts.
Well, I hope you liked the video about batteries. I had a great time putting it together, and I want to think my sponsors at Adafruit Industries. It’s their concept for this. Be sure to drop them a note and let them know that you like this, and better yet, buy something from them. You might check out their MintyBoost, which is a boost converter so you can charge USB devices from double A batteries.
You can always reach me at email@example.com. I love hearing from you guys. Send me your suggestions.