How do batteries work?

After our exploration into plastics and solar cells, we arrive at the question of how to store energy once we obtain it, for example, from the sun.

In other words, we arrive at batteries, the not so perfect solution to energy storage but until now still one of the better ones. On this page, we will dive into the world of batteries.

The history of batteries

Batteries have been around since the 1780s when Italian scientists were studying “medical electricity” using a frog’s leg. It was discovered that the metal used to touch the frog’s leg passed some electrical current. Following this observation, it was demonstrated that by stacking copper, zinc and cloth or cardboard soaked in salt water you get an electrical reaction. This was the start of the first battery (1).

How does a battery work?

A battery consists of 4 main components:

• Anode
• Cathode
• Electrolyte
• Separator

Anode – (negative) is the source of electrons (e) that flow through the external circuit to the cathode as a result of a chemical reaction; the anodic material (M) releases an electron resulting in a positive ion (M⁺), which dissolves in the electrolyte. The battery becomes discharged when no more M⁺ ions can be formed.

Cathode + (positive) accepts electrons (e) from the external circuit, which interact with the cathodic positive ions (M⁺) in the electrolyte to increase the material (M) on the cathode. When the cathodic M⁺ ions are depleted from the electrolyte, the battery can no longer operate and becomes discharged.

Electrolyte maintains the ion balance between both sides of the battery.

Separator provides a barrier between the anode and cathode while allowing the exchange of ions in the electrolyte between both sides of the battery to maintain charge balance (2).

The materials that create the anode, cathode, electrolyte and separator can change from battery to battery.

There are two types of batteries:

• Primary batteries that are not rechargeable and are used until their energy supply is exhausted. In these batteries, the chemistry at the anode and cathode is not usually reversible.

• Secondary or rechargeable batteries in which the chemistry at the anode and cathode is reversible. Charging these batteries with an electric current leads to the reversal of the chemical reactions at the anode and cathode that occurred during discharge (2).

Different types of batteries are required for different purposes:

• some need to be able to go without charging for long periods,
• some are required to be lightweight,
• others need to be able to be recharged many times, etc (2).

Conversation Starter

• What type of batteries do you use most in your day-to-day live?

• What is the main purpose of the batteries you use most?

References

1. Jacobson A, Ted Ed- Ed, How do Batteries work? [Internet]. 2015 May 21. [cited 2019 18 April]. Available from: Ted Ed-Ed (YouTube link)
2. Woodford C, Batteries, a comprehensive page on batteries by explain that stuff [Internet]. 2018 March 27. [cited 2019 18 April]. Available from: Explain that stuff (web link)