Battery 101 – how do batteries work?

Creating and storing energy go hand-in-hand. If you’re interested in generating your own electricity, you should have a working knowledge of how batteries work.

The definition of a battery

What is a battery? The first law of thermodynamics states that energy can be neither created nor destroyed, but fortunately for us, it can be transformed. We can’t store electricity, but we can transform and store it as chemical energy.

That’s what batteries do – a battery is a device that stores chemical energy and converts it into electricity.

The parts of a battery

A battery has three basic parts:

1. a cathode (+)
2. an anode (-)
3. the electrolyte

A standard AA battery has two terminals – one end, or terminal, is positive, and the other is negative. The cathode is the positive terminal, and the anode is the negative terminal.

The electrolyte in the middle is an electrically conductive substance that allows a charge to flow between the cathode and anode.[1] When we connect a light bulb or other device to the cathode and the anode, chemical reactions occur in the battery that cause electrical energy to flow to the device.

A closer look: what are those ions up to?

At the negative anode, an oxidation reaction occurs. Electrically charged molecules from the electrolyte called ions react with the anode, and as a result, electrons are released.

A reduction reaction occurs at the cathode, and as a result the cathode can absorb the electrons produced by the anode.

How does this work?

Electrons repel each other, so the electrons at the anode want to go to the cathode, but the electrolyte stops them. When we connect our light bulb to the battery we use an external circuit; the electrons flow through the external circuit and reach the cathode, and the ions transport the current through the electrolyte.

Why does a battery lose energy, and what happens when we recharge batteries?

The electrochemical process changes the chemicals in the cathode and the anode. Eventually they stop supplying electrons, and this is why a battery contains a finite amount of energy.

Energy only moves in one direction in disposable batteries, i.e. disposable batteries can only transform chemical energy to electrical energy. In rechargeable batteries, the electrochemical processes work in two directions. When a power source such as a solar panel is connected to a battery, the chemical system is reversed and the battery is charged with energy.

Why then, you ask, do rechargeable batteries grow weaker with time?

It’s not entirely clear, but there appear to be different kinds of corrosion that occur over time inside a battery. Corrosion on the terminals affects their ability to discharge, and degradation of the electrolyte affects the transfer of the electric current.[2]

There you have it – batteries, our imperfect little friends. They’re simple in theory, useful in practice, and annoying when they weaken and need to replaced. Current research will (hopefully!) yield a variety of improved batteries in the near future. Maybe those batteries that use quinones will be ready soon?