# The need for electrolytes between cathode and anode in battery

1. May 25, 2014

### Sleepycoaster

My question is simple: Why do batteries need electrolytes? Wouldn't the battery need the charge to flow only through the circuit in the device being powered? The point of the anode and cathode's separation is to preserve the potential difference, so why allow charge to flow through an electrolyte?

2. May 26, 2014

### Matterwave

A battery is different than a capacitor. A capacitor is what you're thinking of, it will simply discharge the charge it has accumulated. A battery, on the other hand, maintains a voltage through a chemical process. It produces an electro-motive force through the reaction of the anode and cathode with the electrolyte. When a batter drains, it's voltage stays roughly constant (because the chemical reactions are driving the voltage), while when a capacitor drains its voltage drops as it loses charge.

3. May 26, 2014

### Staff: Mentor

Typical alkaline AA battery has a capacity around 2Ah. Calculate how much charge it could push through the outside circuit in its lifetime. Assuming circuit is not closed, this charge has to build up somewhere. Let's assume charge builds up at the ends of the battery - they are separated by 50 mm. Try to calculate force that would attract both ends. This is a trivial application of Coulomb's law.

Now, compare that force with force required to lift Eiffel tower. Or better yet, to the gravitational attraction between Earth and the Moon.

4. May 26, 2014

### DrDu

That's the meaning of "circuit", the current also flows inside the battery. A battery is not different in this respect from other sources of current, like, e.g., a dynamo. As Borek already pointed out, the reason is to avoid built up of (more than very small amount of) charge on the electrodes which would immediately stop the current.