Cells and Batteries

Let’s take a moment to think about the word cell. As we have discussed, a galvanic cell is a pair of half-reactions connected in such a way that the movement of electrons created can be used. The important piece of that definition is the “a” . In other words, a cell is a SINGLE pair of half-reactions. 

That means that if we choose to match the strongest and weakest half-reactions, the highest potential chemistry can give us is 5.92 V, by using the two half-reactions here:

\(Li \rightarrow Li^{+1} + e^{-1}\)

\(F_2 + 2~e^{-1} \rightarrow 2~F^{-1}\)

That raises the question, how do we make 9V batteries?

The answer to that question is that a battery is simply more than one cell connected in series.

Here’s what that means. This is a cell. We may call it a battery, but it isn’t. It’s a cell containing a single pair of half-reactions producing 1.5 V. That's why one of the companies that makes lots of these is called \(Duracel^®\).

On the other hand, this is a battery.

Note that there are two cells, stacked so that the positive end of one, touches the negative end of the other. Connecting the cells in this way, adds their potential, so this flashlight runs on 3V (1.5V + 1.5V).

This distinction is is important when you are learning about galvanic cells, electrolytic cells, hydrogen fuel cells and more although, admittedly, most of us just call them all batteries when we're out in the "real world."