What is a battery?

What is a power cell, and how does the chemistry work?
09 May 2023

Interview with 

Dave Ansell, Sciansell




First, we need to understand exactly what a battery is. In the year 1800, when the first battery was made, the person to ask would have been the Italian chemist Alessandro Volta - from who we get the word “Volt” - who stacked up a pile of copper and zinc plates and showed that they produced electricity. We don’t have Volta to ask, but we do have the next best person: the formidable science communicator and demonstrator, and former Naked Scientist, Dave Ansell, who has turned up armed with lemons. You come bearing gifts.

Dave - I have come bearing many lemons.

Chris - What are you doing with them?

Dave - So I thought we could start off by recreating Volta's original experiment. I've got some copper, a copper nail, which you'd used to hold on a slate, and a zinc covered nail. Just a standard nail. And I have a lemon and they're connected with wires to a voltmeter, which measures basically how hard the electricity's being pushed around the circuit. And if I put the copper nail and the zinc nail in...

Chris - Dave is just stuffing the two nails into the lemon. I'm not going to use that in a cocktail. Now it's got zinc in it by the look at it. But they're close together, they're about centimetre apart, and they've got crocodile clips securing them to your voltmeter. And I now see on the voltmeter it's gone from reading 0 to 0.94 Volts

Dave - Yeah. So nearly a Volt.

Chris - So nearly a Volt is coming out of that lemon.

Dave - So not quite as much as the battery you'd buy in the shops, but it produces a current.

Chris - So why are we seeing a voltage when you stick in those two metals? And what would happen if you stuck two of the same now? Because I noticed you have used a copper and a zinc nail like Volta did. Why is it got to be two different metals?

Dave - So, we can try putting two the same nails in

Chris - Two zinc nails going in and it says there is no potential there.

Dave - Yeah. So what's going on is you've got two chemical reactions going on in this case. On the zinc, there's a chemical reaction where the zinc atoms are losing electrons and the copper end, it's gaining electrons. It's probably actually the copper oxide that is gaining electrons and turning back into copper. Those two reactions can't happen on their own because you've got to lose electrons from the zinc and you've got to gain electrons on the copper. And so the only way they can carry on is by pushing electrons around the circuit and then back to the other side.

Chris - I see. So if the two were touching each other, physically touching, there wouldn't be a voltage documented on the voltmeter because it would literally jump from one metal to the other. The zinc wants to give away those electrons and dissolve. And the copper wants to grab them and get rid of the copper oxide on its surface and turn into copper. And it's because they're separated.

Dave - Yes. Because the only way that it can happen is by pushing electrons around. If they're touching, it's actually really bad. It's a big problem in boats and things. You've got two different metals touching each other. You get a battery and it will just flatten the battery and you oxidise your boat very quickly.

Chris - So what's the lemon for?

Dave - So it's letting it balance out the charge. So you've got to push electrons around the circuit, but if you're not careful, then one side will get very positive and the other side will get very negative. So the lemon, all it does is it allows charged ions, so charged atoms, to move around and balance out the charge. It doesn't actually have to be a lemon. I've got some salty paper down here and you should find it does exactly the same thing.

Chris - You've got almost 0.9 Volts on your multimeter. So it's just the ability once you make some zinc dissolve, you can get the dissolved zinc out of the way and more zinc can then dissolve. It's not getting crowded with trying to dissolve zinc and the same is going on at the copper.

Dave - And also it is slowly getting more and more negative at the zinc side and more and more positive at the other side. You've got to balance out the battery, you've got to balance out the charge within the battery.

Chris - Otherwise no current could flow. Obviously we don't power out electrical devices with lemons, with nails hanging out of them. So when we look at a compact cell as we should strictly call it, that we put in say a phone or into a TV remote or something, what actually is going on in there and why do you see different flavors of them? Some say alkaline batteries, some say zinc chloride. I mean what's that all about?

Dave - There's basically lots of difference, if you use different metals, you get different voltages. So we can try, instead of using zinc, we can use basically some stainless steel and that will produce a much, much lower voltage now 0.15 Volts.

Chris - Yeah, you've got virtually nothing with that.

Dave - So if you want to use different voltages, you can use different chemistries and different chemistries can store different amounts of energy in the same space. Lithium iron batteries, which are the big funky ones, work rather differently than this simple way. They're less of a chemical reaction. You've got a load of lithium ions, which would rather be in one material than another material. And so naturally, they'll want to flow from one to the other, but you can push them back by charging it up. And if you let a current flow, it'll flow back again. So it acts as a rechargeable battery.

Chris - So the objective is then to try to explore new combinations of metals or arrangements of the chemistry to try to get the right sort of compromise of what voltage you want and how much energy it can store.

Dave - Plus there's also a load of really evil stuff going on because there's not necessarily one thing, one reaction going on. There can be hundreds of other little side reactions going on, and quite often they can cause havoc in your battery. So actually what most of the research is going on is producing a battery, which will last a thousand cycles. Rather than just work twice and then give up the ghost for something else. You made something else and it fails and stops working.


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