The first battery was
created by
Alessandro
Volta in 1800. To create
his battery, he made a
stack of alternating
layers of zinc, blotting
paper soaked in salt
water, and silver. This
arrangement was known as
a voltaic pile.
The top and bottom
layers of the pile must
be different metals.
When
you attach a wire to the
top and bottom of the
pile, you can measure a
voltage and a current
from the pile. The pile
can be stacked as high
as you like, and each
layer will increase the
voltage by a fixed
amount.
In the 1800s, before the invention of the electrical generator (the generator was not invented and perfected until the 1870s), the Daniell cell was extremely common for operating telegraphs and doorbells. The Daniell cell is also known by three other names:
-
Crowfoot cell (because of the typical shape of the zinc electrode)
-
Gravity cell (because gravity keeps the two sulfates separated)
-
Wet cell (because it uses liquids for the electrolytes, as opposed to the modern dry cell)
The
Daniell cell is a wet
cell consisting of
copper and zinc plates
and copper and zinc
sulfates. To make the
Daniell cell, the copper
plate is placed at the
bottom of a glass jar.
Copper sulfate solution
is poured over the plate
to half-fill the jar.
Then a zinc plate is
hung in the jar and a
zinc sulfate solution is
poured very carefully
into the jar. Copper
sulfate is denser than
zinc sulfate, so the
zinc sulfate "floats" on
top of the copper
sulfate. Obviously, this
arrangement does not
work very well in a
flashlight, but it works
fine for
stationary applications.
If you have access to zinc sulfate and copper sulfate, you can try making your own Daniell cell.
Inside the battery a chemical reaction produces the electrons. The speed of electron production by this chemical reaction and the battery's internal resistance controls how many electrons that flow between the terminals. When a load is applied to the battery, electrons must travel from the negative to the positive terminal for the chemical reaction to take place.
Learn about the electrochemical reactions used to create batteries with easy to do experiments you can try at home. To do these experiments accurately, you will need a volt-ohm meter that has the ability to read low voltages (in the 1-volt range) and low currents (in the 5- to 10-milliamp range). This way, you will be able to see exactly what your battery is doing. The ability to harness this sort of reaction started with the voltaic pile.
In this simple experiment you can create a voltaic pile using coins and paper towels. Mix salt with water (as much salt as the water will hold) and soak the paper towel in this brine. Then create a pile by alternating pennies and nickels. See what kind of voltage and current each pile produces. Try a different number of layers and see what effect it has on voltage. Then try alternating pennies and dimes and see what happens. Also try dimes and nickels. Other metals to try include aluminum foil and steel. Each metallic combination should produce a slightly different voltage.
Another simple experiment you can try involves a small jar, dilute acid, wire and nails. Fill the jar with lemon juice or vinegar (dilute acids) and place a nail and a piece of copper wire in the jar so that they are not touching. Try zinc-coated (galvanized) nails and plain iron nails. Then measure the voltage and current by attaching your volt meter to the two pieces of metal. Replace the lemon juice with salt water, and try different coins and metals as well to see the effect on voltage and current.
The simplest battery you can create is called a zinc/carbon battery. By understanding the chemical reaction going on inside this battery, you can understand how batteries work in general.
Imagine that you have a jar of sulfuric acid (H2SO4). Stick a zinc rod in it, and the acid will immediately start to eat away at the zinc. You will see hydrogen gas bubbles forming on the zinc, and the rod and acid will start to heat up. Here's what is happening:
-
The acid molecules break up into three ions: two H+ (hydrogen) ions and one SO4-- (sulfate) ion.
-
The zinc atoms on the surface of the zinc rod lose two electrons (2e-) to become Zn++ ions.
-
The Zn++ ions combine with the SO4 ion to create ZnSO4 (zinc sulfate), which dissolves in the acid.
-
The electrons from the zinc atoms combine with the hydrogen ions in the acid to create H2 molecules (hydrogen gas). We see the hydrogen gas as bubbles forming on the zinc rod.
Now stick a carbon rod in the acid, the acid does nothing to it. Now connect a wire between the zinc rod and the carbon rod, two things change:
-
The electrons flow through the wire and combine with hydrogen on the carbon rod, so hydrogen gas begins bubbling off the carbon rod.
-
There is less heat. You can power a light bulb or similar load using the electrons flowing through the wire, and you can measure a voltage and current in the wire. Some of the heat energy is turned into electron motion.
The electrons go to the trouble to move to the carbon rod because they find it easier to combine with hydrogen. There is a characteristic voltage in the cell of 0.76 volts. Eventually, the zinc rod dissolves completely or the hydrogen ions in the acid get used up and the battery "dies."
That is why a battery can sit on a shelf for a year and still have plenty of power.
