How does a battery work? Well, it is surprisingly simple, they use a chemical reaction between the “battery acid” and two different metals to make one side have too many electrons (negative side) and one side have too few (positive side). Wait, how does that make a battery and current? Well, I’ll tell you and along the way, I will tell you why some materials conduct electricity and some don’t, what current actually is, how every science teacher and electrician in the world is lying, and the importance and meaning of “free electrons” and ions: don’t worry it’s actually pretty easy (for chemistry). Ready, let’s go…
In order to understand how a battery works and what current is, I need to define two terms: “free electrons” and “negative ions”. To do that, I should start with the basics. Objects are made of atoms. Atoms have a heavy positively charged center (or nucleus) and have a cloud of negatively charged electrons that are stuck (or bonded) to the nucleus.
If that was the whole story then we would have no current or electricity. However, certain elements don’t hold on to their outer electron very strongly and the electron can escape the pull of the nucleus and basically roam free. This is called a “free electron” (good name eh?). When the electron escapes, the atom is left with one more positive proton than a negative electron so it has a positive charge and is called a positive ion.
To recap: Electricity depends on negative tiny “free electrons” that aren’t stuck to any particular atom and heavy positive ions (atoms that have lost an electron or two).
Current is made of flowing electrons – that is all current is. Now the individual electrons do not move very far but they basically set up a wave of electrons moving in generally the same direction. Metals have a lot of “free electrons” and ions so electrons can flow easily through them, they are called conductors. Plastics have very few “free electrons” and ions so electrons cannot easily flow through them: they are called insulators. This is why a wire is made of metal for the current to flow through with plastic insulation to keep the current from flowing out of the wire into, say, your hand.
So, how do you get the electrons to move in a metal? One way is to use a battery. Look at any battery it always has a positive side and a negative side. The negative side has too many electrons and the positive side has too few. Opposites attract and like to repel so the negative electrons want to get away from the negative side and are attracted to the positive side. If you connect the sides with a conducting wire the electrons flow through the metal and into the positive side.
[SIDE NOTE: I am about to blow your mind. You might have been told that current flows from positive to negative, that is because Ben Franklin came up with the idea of positive and negative charges in 1745. At the time he arbitrarily and insistently stated that electricity (or as he put it electrical fire) flowed from positive to negative. It took a further 150 years before the discovery of the electron. By that time, we had equipment and classes and rules assuming current flowed from positive to negative. So, instead of reversing all electrical equipment and rules, they decided to just well, ignore reality. We say current flows one way when what really is going on is that the electrons are flowing the other way! In other words, every science teacher and electrician in the world is lying. Crazy right?]
OK, but I still haven’t told you how a battery works. How does a battery create and maintain a positive and negative side? Well, every battery uses the interaction between two types of metal and an acid or a base. Acids have chemical reactions that move the free electrons and bases have chemical reactions that move the positive ions, but either way, they leave the positive side with too few electrons and the negative side with too many.
The original battery in 1800 was just strips of silver and zinc in a cup full of saltwater (as the acid). This made a very weak battery but the saltwater would react with the zinc to add electrons and react with the silver to remove electrons. Soon people were making batteries with plates of different metals in a bath of acid. In fact, the modern lead-acid car battery is just plates of lead and lead sulfate in a pool of acid.
However, acid is inconvenient as strong acids tend to eat away at the container of the battery and the liquids are easy to spill. In 1899, we started using bases instead of acids as the chemical, and most modern batteries today use a base as their chemical.
There are many types of batteries used today but let’s look at a typical Alkaline battery. Alkaline batteries get their name because the word alkaline is another word for the base (Chemists always have multiple names for the same thing – drives me nuts). Anyway, alkaline batteries come in many shapes and sizes but inside they all tend to have the same metals and chemical reactions. So, let’s look at what is going on inside an alkaline battery.
Inside a battery, there is a column of ground zinc mixed with the base chemical potassium hydroxide. Surrounding the zinc is a different metal called manganese oxide. The potassium hydroxide chemically reacts to the zinc and removes positive ions leaving that side with too many free electrons and a net negative charge. The chemical also reacts to the manganese and adds ions leaving that side with too many positive ions and a net positive charge. The zinc and manganese are separated by a plastic sheet so that the electrons don’t just flow over to the positive side with the ions. Therefore, the electrons in the zinc side are stuck there. They move as far away as they can from each other and congregate on a nail (called a “current pick up”). This reaction occurs until the charges on both sides create such a strong electromotive force that the chemical reaction stops occurring. In a typical alkaline battery, that is 1.5 Volts.
When the battery is placed in a circuit, where the electrons can flow in a conductor to the positive side of the battery, the chemical reactions occur again to keep the electromotive force at 1.5 Volts. When the chemicals in the base react with the metals the chemical becomes less powerful. Over time, the chemical loses its power of reaction and the zinc runs out of ions to move at which point the battery is “dead”.
Alkaline batteries are not rechargeable batteries. However, rechargeable batteries work the same way as disposable batteries in that a chemical moves over ions or electrons so that the positive side has too many positive ions and the negative side has too many electrons. However, rechargeable batteries reverse the chemical reaction when current is forced through them in the “opposite way” so that the ions move back to their original metal and the chemical base or acid becomes stronger again.
Different batteries use different metals and different chemicals and different geometries but they all use either a base or an acid and two types of metal (or metal compounds) to make the negative side have too many electrons and the positive side has too many ions. And that is how a battery works!
I told you it was simple… for chemistry!