Saltwater Battery

How it Works

A saltwater battery consists of:

Plastic cup (glass also works, it cannot be metallic)
Copper strip
Zinc strip (we can use different metals provided that they have a different reduction power, but these are the most common in these types of batteries. Different metals will equal to different levels of energy output which are related as well to their reduction power.
Electrical cables
Salt and water

The dissolved salt in the water separates into positive and negative ions, which makes the electrical conductivity of the salted water considerably higher than normal water. The resistance then translates into energy dissipation, which in this case, is heat.This battery follows Alessandro Volta’s rules, as we explained in the last presentation, but basically says that if we combine two different metals, there will be exchange of electrons between them, one being negatively charged and the other one positively charged. With this, one of the metals will attract the positive ions and the other metal will attract the negative ions, in which we can call this a redox reaction.

Since we also have a connected cable, we will have voltage between the two metals (around 0,8 V), creating an electrical current that will give power to the car.

Interesting facts

More cups, more energy

Although one cup is probably enough to create the energy needed to make the car move, if we wanted to add more energy, we would need more cups, which would need to be added in series, just like on an electric circuit, so that voltage increases (electric current however does not; for that we would need an ionic solution that has higher electrical conductivity).

Battery life

This battery cannot last forever because redox reactions at some point, would stop occurring as, after some time, the metals would be oxidized. This can be solved however by sanding the metals, but you need to keep in mind that this is not an unlimited process as at some point, you will run out of metal to sand.

Temperature variation

You can do this battery using cold water, but if you use hot water, the internal energy of the system will increase. This occurs because when we are heating water, although the internal gravitational energy would stay the same, the internal kinetic energy will increase, as the molecules of water will start to move faster. More internal kinetic energy equals to faster redox reactions, which will increase the energy output.

Oxidized metals

It is not recommended to keep the metals always immersed in the saline solution when the battery is not being used because the redox reactions will continue to exist, creating a layer of oxides on the metals. Such oxides are bad conductors and their arrangement in the electrodes will create a gradual insulating protection in metals, preventing the circulation of electric current.