Batteries are not easy to get, you have to leave the comfort of your home and go down to the store, to buy the batteries. Also, batteries are not cheap too. 1 Pack of Energizer (2 batteries) costs $2.20 excluding GST, which means 1 battery costs $1.10. Our goal is to make homemade batteries that produces enough energy, are easy to make, and cost less. 

We decided to use coke, something that is inside everybody's fridges, to make a battery.

This is the diagram of our battery. That brown liquid is the coke. The white strip is zinc, and the brown strip is copper. Crocodile clip wires are clipped to the strips and connected to the voltmeter.

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Our idea to make a battery is quite simple, and cheap too. The time taken to make the battery is also significantly lesser than having to go down to the store to buy one. And, it is also rechargeable! Rechargeable batteries are generally more expensive than regular ones, but with our coke battery idea, a battery can be easily recharged by refilling the can with more coke!

Background Research

Background research on why coke produces a voltage.

The copper holds onto its atoms more strongly than the zinc does. The zinc strip is therefore more negative than the copper strip, and the electrons flow from the zinc to the copper.
When the forces are eventually balanced, the copper strip ends up with more electrons than the zinc strip. The zinc strip now has fewer electrons, and it cannot attract the zinc ions back to the strip.

If our battery just had water in it, not much more would happen. But our Coca-Cola battery has water plus phosphoric acid. An acid is something that has an easily detached hydrogen ion. Hydrogen ions are positive, and the remaining part of the acid becomes negative when it loses the hydrogen ion. In our battery, the remaining part is the phosphate ion.

So what happens when all of those positively charged zinc ions bump into those negatively charged phosphate ions? The phosphate ion is more strongly attracted to the zinc ion than to the hydrogen ion. The positively charged hydrogen ion is attracted to the copper strip, because the copper strip has the extra electrons, and is thus negative.

The hydrogen ions attract the electrons from the copper, and become neutral hydrogen atoms. These join up in pairs to become hydrogen molecules, and form bubbles on the copper strip. Eventually the bubbles become big enough to float up to the surface and leave the system entirely.

Now the copper strip no longer has the extra electrons. It attracts more from the zinc strip through the connecting wire, as it did when we first connected the wire. The copper ions next to the copper strip are not as attracted to the strip as they were before. The hydrogen ions keep taking the electrons that attracted the copper ions. So those ions are free to move through the liquid.

At the zinc strip, zinc ions are being removed, leaving extra electrons. Some of those electrons travel through the wire to the copper strip. But some of them encounter the copper ions that happen to bump into the zinc strip. Those ions grab the electrons, and become copper atoms. We can see those atoms build up on the zinc strip. They look like a black film, because the oxygen in the water combines with the copper to form black copper oxide. Eventually, all of the zinc is eaten up, and the copper and copper oxide falls into a pile beneath where the zinc strip used to be. The battery is now dead, and no more electrons flow through the wire. If there was not a lot of acid in the water, it may be the first thing to be used up, and the battery may die while there is still some zinc left on the zinc strip. (FIELD, 2015)

Background research on why salt decreases the voltage produces.

What happens exactly when salt is dropped into coke?
Dropping salt in soda causes the salt to dissolve and subsequently reduce the availability of the soda's solvent to dissolve the carbon dioxide, which is due to the increase in solutes causing a change in the balance of the soda's chemistry, also causing the soda to release some of its carbon dioxide. The salt falling into the soda allows for the formation of nucleation sites for carbon dioxide bubbles. These bubbles transition to the surface and cause the bubbling effect you notice after pouring salt into soda. The salt dissolving into the soda causes a change in the pH balance of the solution. In return, the pH shift causes a decrease in the solubility of the carbon dioxide, thus releasing CO2 gas, or the bubbles you see when salt is combined with soda.

How does this decrease the voltage produced?
As the battery heavily relies on the acid in the coke for it to work, the pH shift caused by the salt will cause less acid to produce voltage. This in turn leads to lower readings on the voltmeter. (KILHEFNER, 2015)

For more information, see our proposal.