I would like to start this episode with a question to you, the listener. Ask yourself how many devices can you spontaneously think of that use a battery? I believe there is a high chance that you are listening to this podcast from one such device, either your smartphone or your laptop, but I am sure you can name more than those too. There are so many from electronic devices such as the aforementioned phones and laptops to medical equipment such as pacemakers, both cardiac and neural, all the way to yeah, simplest devices like flashlights and clocks. I think it is fairly safe to say that the invention of batteries has revolutionized our worlds. My name is Johannes Vogel and you are listening to chemistry in everyday life. My podcast where I explain the chemistry that happens all around us in layman's terms. Chemistry is a study of the attributes and changes that substances can undergo, the matter of their gases, liquids or soles. Believe me when I tell you that this happens everywhere around us, at this very moment. So batteries in a nutshell are devices that provide portable electricity and it does that with the help of a very basic chemical concept called redox reactions. Effectively what we need for electricity to occur is a circular flow of ions or electrons. So essentially we have an electrical circuit that is being closed by the battery. So how can we create electrons chemically? The answer as I mentioned before is a so-called reduction oxidation reaction, short redox reaction. Let me explain those fancy terms briefly. When a compound loses an electron it is said to be oxidized. That means the process of losing an electron is called oxidation. Conversely when a compound obtains an electron it is said to be reduced. The process of gaining an electron is called reduction. To remember this there was an acronym that I learned at high school. Oil rig. It is short for oxidation is loss of electrons. Reduction is gain again of electrons. I don't know what it is with acronyms but this particular one really stuck with me. But why exactly certain elements lose electrons that is they are oxidized and why others gain electrons that is they are reduced depends on the option to attain a better stability. Just one example of an observation that was made. There are several others which are a bit too much for this episode but so broadly speaking the most stable elements are the noble gases like helium or neon. That is why they are called noble gases because they are so stable it is beneath them to react and interact with the commoners, the common elements like lithium and chlorine. Every other element close in structure to a noble gas. This is again broadly speaking. Tries to attain as many electrons as the nearest noble gas. So if an element has one electron to many it tries to lose it and gets oxidized in the process. This way then it has the same amount as noble gas. That would be for example lithium. On the other side if one element lacks one electron to achieve that zen state of noble gasness it looks to take one electron from the environment so tries to get reduced. This likelihood can even be measured. It is called the electrode potential and is measured in the unit volts which is quite not so incidentally the unit one uses to describe the power of a battery. So you see the combination redox reactions and batteries is quite intertwined. So redox reactions are reactions between one side losing some electrons and the other side gaining some. If you let this all happen in one pot inside a solvent for example water with some table salt in it you would most likely notice that the solution becomes hot, sometimes very, very boiling hot. And that's not really what you want. Just to remind ourselves what we do want is a controlled flow of electrons or ions from one end to the other via the electric circuit that we so conveniently set up so that all that fancy stuff can happen. Whatever that fancy stuff is like telling the time and beeping when a set time is reached or going on Twitter, what you call that or to call someone you name it whatever that just is. Well, the way to do this as laid out by people far more clever than I am that is to first isolate the part of the redox reaction that gives the electrons from the part that accepts the electrons. So visually speaking you want to have two separate buckets. Then you connect them with for example a wire with your device in between that should do it. But unfortunately it kind of doesn't because we have not closed the circuit yet. What you also need is a connection between the two buckets that allows the electrons to flow back but not the solid elements themselves. This is a medium called an electrolyte. Usually there's some kind of ionic gel solid or something in between and this then closes the circuit and electrons flow. As is always the case theory is awesome but it is abstract. So let's run through a visual example. I've spoken mostly about electrons but in this case it is actually ions that are moving but I use it because we can easily visualize it. This is something called a galvanic cell. The idea is the following. If you had a bucket of water and you dissolve the salt in it called copper sulfate which is copper with two less electrons than in its neutral state and then you dropped in a solid piece of the metal zinc. You would see a dark solid forming on the surface of the zinc metal. This is solid copper metal that took two electrons from the zinc and became solid. In turn the zinc would become zinc 2+ because it loses two electrons and goes into solution as zinc sulfate. In the process the water solution would warm up as this reaction creates heat. Now we have two buckets. These can be referred to as half cells, one with zinc sulfate in water and one with copper sulfate in water. And you submerge in the bucket with zinc sulfate a solid rod of zinc metal. And in the copper sulfate a solid rod of copper metal. And then you connect those two rods with a wire each that connects to something that can measure a voltage. Like a voltage meter I guess. Clever your harness. So now all we need is something that allows passing of ions between the two buckets. And that would be in this case a gel with potassium sulfate, something called an electrolyte as I mentioned before. In this situation the voltage meter would measure some voltage while the zinc metal goes into solution as zinc 2+ and then that would become less and less metal. And the zinc metal would be used up. On the other side the copper rod would become more as the copper sulfate is reduced. That is it receives electrons to become copper metal. Over time because you will have less copper 2+ than sulfate in the water solution you will find that zinc 2+ traveled through the gel to the other side to even out the amount of metal ions to sulfate because it always has to be 1 to 1. The reaction would stop once all the zinc is used up. Which is also the moment when the galvanic cell stops giving electricity. That means it goes flat. So this is the concept of a battery. But I was talking about two buckets and wires and gels in a tube. Not exactly something you can put into your pocket for use in smartphones right. So let's talk now about a real life example. So if we take one of the most commonly used batteries around the world, an alkaliene battery of any manufacturer, in there we see everything that I just described. Alkaliene are called alkaliene because other batteries are acidic in nature. Alkaliene is the opposite of that. And alkaline substance is, for example, potassium hydroxide.
is mixed with a zinc in powder form, and all of that in a gel. Gel to make it easier hand-lo-able. This part at the center of the battery is connected to the negative outlet of the battery, the flat bit. That is the part that is oxidized. That means it loses electrons and turns into a compound called zinc oxide. The name of that is not really important. And this gel, you have a physical barrier to the other half cell that allows ions or electrons to go through, but not the metal itself. That is typically something like cellulose. This is the electrolyte that is there to make sure the battery does not short-circuit itself. And around that, you have another paste consisting of a manganese dioxide and carbon powder. The carbon is therefore better conductivity, but the thing getting reduced is the manganese dioxide. That is to something called die manganese trioxide. Again, not super important other than this is what drives the electric current, but the names don't worry about them right now. The fact is that we are turning two compounds into different compounds as electrons move through. The construction itself has more things around it, but it always centers around either safety, such as let's make sure the alkaline solution does not leak out, which is bad for the environment and really dangerous for children. Or let's improve conductivity and make it a better battery regarding lifetime and storage. So that is what a non-rechargeable battery looks like. You can find them in your standard formats like double A or triple A or whichever format you can think of. Before we move on from here, I wanted to briefly come back to what I said earlier about a Redox reaction happening all in one place would just cause the solution to heat up. A couple of years ago, there were reports of portable devices manufactured by Samsung that overheated or even exploded. Now that we looked at the construction of a battery, you can maybe appreciate what happened here. To my understanding, the issue was that the electrolyte, you know, the barrier between the two halves of the Redox reaction was damaged or faulty, which can happen if you inadvertently bend the battery. The Redox reaction then happened all in one place, which caused a lot of heat. Gas is formed and when you have rapid formation of heat and gas, what you can get is an explosion. So this is what happened there, okay. You may have noticed that so far, I did not mention anything about rechargeable batteries. The reason for this is rather simple and that is that non-rechargeable ones are simpler to discuss the concept and second, the principle stays the same. The only difference is that attaching the rechargeable batteries to an electric current allows us to reverse the Redox reaction in the case of rechargeable batteries. This process is never perfect or not perfect, I don't know if never, maybe someone will find it out. And over time, it changes the structure of the battery and renders it less performance. So yeah, the chemical structure on the reverse process may not always yield the compound that we started out with. This is dependent on quite a few factors such as external temperature. Is it zero degrees Celsius or 60? How fast is the battery charged? Which materials are used? And you know, the list goes on, it's quite complex. Rechargeable systems such as the well-known lithium ion batteries that you can find in smartphones, are carefully developed to allow for a maximum amount of recharge in the longest possible time to supply the device with enough electricity. You'll actually find that every year there are millions invested in developing better batteries as they still have advantages and drawbacks, especially the drawbacks you want to address. Which brings me to my last point about batteries. One of the big issues is recyclability. First off, it is absolutely possible to recycle batteries. But it is currently hardly done. Because mining the materials is still cheaper in many cases. Nonetheless, batteries contain toxic materials. So many regions such as the USA and the European Union have passed laws that forbid throwing batteries in the solid waste bins. Which would then end up in landfills and in turn the batteries may then degrade and contaminate the ground. In the worst case, getting into the ground water and then drunk by animals and humans. Recycling currently still complex. But efforts are made and with more and more electric cars being produced, we may actually see improvements in procedure that may make this a more profitable avenue to go down. With this being said, although there's much, much more to talk about, I shall leave it at that. As I said, batteries, think about how often we use them. Then assume there are 10 more applications around you that use them too. I mean, seriously, what a game changer if you think about it. If you're not convinced of that, try and find an electric socket in a forest would you? So yeah, anyways guys, I hope it was reasonably clear and you enjoyed this episode. If you have comments or ideas for new topics, please leave comments on Twitter under Atk Chemistry in Eve 1 or right directly to me under
[email protected]. If this was too fast to write down, I left as usual the information in the show notes. Also if you liked what you listened to, please rate my show on the podcast platform of your choice. Thanks a lot and take care folks. You've been listening to Chemistry in everyday life. A podcast about chemistry that happens all around us explained in layman's terms. Thank you for listening. [Music]
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