Chris - What actually is a battery? How does it work?
Fiona - So, a battery is electrochemical device. So, it converts chemical energy into more useful electrical energy and it does this via oxidation and reduction reactions which involve the loss and gain of electrons respectively, which then go around the external circuit to then produce electricity. The three main components to make this happen, you need to have 2 electrodes Ė the cathode, the anode, and you need an electrolyte which is ionically conductive, so that the ion or the charged species can be transported.
Chris - So, when I look at a battery which I might pick up from the supermarket or take out from my alarm clock, if I were to open one up, what would I see inside?
Fiona - One of the classic examples to look at is one thatís used in most laptops, phones, tablets at the moment, developed by Sony in 1990. It uses graphite as the anode, so itís got carbon.
Chris - Itís a carbon like a pencil lead actually.
Fiona - Exactly, which has the sheets of carbon, which the lithium get intercalated or inserted in-between these sheets of carbon. In the cathodes, youíve got a material called lithium cobalt oxide which has a similar layered structure to graphite but instead of carbon, itís cobalt dioxide. And then the lithium is in-between these sheets.
Chris - Does that make the power though?
Fiona - So then, the cobalt is in a 3 plus charge state and then it can go to the plus 4 then the lithium ion then goes across the electrolyte and it goes into the graphite while the electron goes around the external circuit then they recombine. And thatís how you get your electricity.
Chris - So, once all the lithium has made that journey, thatís when the energy is spent from the battery.
Fiona - That was in the discharge state. That was actually charging the battery and then to use it, the reverse process happens. So, this is a rechargeable battery. So, the lithium ions can then rock back and forth because now, the cobalt 4 plus could go to the cobalt 3 plus state then the lithium goes from the intercalated graphite sheets, goes across the electrolyte into cobalt dioxide layers, and the electron goes around the external circuit. So, it was called the rocking chair battery because the lithium rocks back and forth. You can think of it like a Victoria sponge with the two layers of cake as the sheets of cobalt oxide, the jam of lithium inside.
Chris - I love the analogy. I wouldnít like to eat a battery though. There's lots of very toxic things in it.
Fiona - Yeah, I wouldnít advice it.
Chris - Shall we build one?
Fiona - Yeah. So, what we make in the lab is called a coin cell battery or button battery which is used in a lot of watches, phones, clocks.
Chris - The little thing, they look a bit like a coin, donít they?
Fiona - Yeah, exactly. So, youíve got the stainless steel base and Chris, you can have a go at making one.
Chris - Itís like a little saucer, isnít it?
Fiona - Exactly. So, just to proove how easy it is and then weíve got our cathode material which is a lithium cobalt oxide which we have as just a piece of paper today.
Chris - That would sit inside the base, just against the base.
Fiona - Exactly. But then you need to have this rubber gasket sat inside the base because you can't have an electrical contact between the anode and a cathode or else it would be a short circuit.
Chris - Itís a short circuit inside the battery, wouldnít it? Yeah, okay.
Fiona - Exactly. And so then, we have ourÖ
Chris - So, I've got my gasket. So, I basically got little cup like a stainless steel cup and I've got my chemical in the bottom thatís the lithium cobalt oxide thatís going to be one source of the charge. Now, I've put a rubber disk in there to separate it. Then what do I put in next?
Fiona - Yeah, exactly. Because the electrolyte is a liquid electrolyte, we need to have a physical barrier between the anode and cathode. Itís a glass fibre that sits on top of the cathode and then you would soak it in electrolyte and then we can place our anode on top and then we need a stainless steel current collector and to ensure that we have a good electrical contact between our anode and our cathode and thenÖ
Chris - Okay, thatís now a little sort of disk that goes on on top of the sandwich.
Fiona - Exactly and then the top of our battery which is a kind of like another saucer like the base.
Chris - And just plugs inside.
Fiona - This coins cell battery, you can think of it as a AA battery or AAA by just rolling your sheets of anode, cathode and electrolyte, and then place in a cylindrical case.