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How does that work? Batteries

How does that work? Batteries

We put them in stereos, computers, watches, torches, phones and cars without a second thought. But what is it about a simple battery that allows them to be so versatile?

The first battery was made by Alessandro Volta in 1800, his simple idea involved alternate layers of zinc, wet salty paper and silver. By putting a wire from the bottom to the top layer, the voltage can be measured – the bigger the stack, the more volts you can get.

Batteries are devices in which chemical energy is directly converted to electrical energy - basically they are just small chemistry labs that produce electrons. They all have more or less the same characteristics – a positive and a negative end, and a cylindrical (or square, round, etc.) section in the centre that holds the chemicals.

Batteries can sit on the shelf for years because unless the ends are connected to something, or each other, there is no chemical reaction. This does, however, vary with temperature and sometimes batteries will lose a little charge because of chemical reactions that occur in the cell if they are not topped up. As soon as you connect it to something, electrons (negatively charged particles) start whizzing from the negative end towards the positive end – creating a circuit.

Car batteries - lead acidRechargeable batteries can be re-charged after they have been drained. This is done by applying an external current through an electric charger, which reverses the chemical reaction inside the unit and allows it to be used again. Normal battery cells cannot be recharged, since the chemical reactions are not easily reversible.

The battery industry is worth 2.8 billion dollars annually, and making them is still one of the most resource-consuming of activities, and often involves hazardous chemicals. Many batteries can now be recycled in order to reduce the amount of toxic waste and recover some of the more useful materials inside them.

There are a number of modern batteries that are used, each with different internal chemistry. Some of the more common ones are:

Zinc-carbon battery – used in all cheap AAA, AA, C and D cell batteries. These are the simplest batteries, which contain zinc and carbon electrodes with an acidic electrolyte between the metallic layers.

Alkaline battery – Used in Duracell and Energizer batteries, the electrodes here are zinc and manganese-oxide, with an alkaline electrolyte.

Nickel-cadmium battery – The ‘NiCd’ batteries have nickel-hydroxide and cadmium electrodes, with potassium-hydroxide as the electrolyte – they are often rechargeable, but suffer from the ‘memory effect’ which prevents batteries recharging to their full original level. These are used in many domestic applications.

Nickel-metal hydride battery – an increasingly more popular battery, similar to the NiCd batteries but with no memory effect – making them much more long lasting when recharged. NiMH batteries can have two to three times the capacity of an equivalent size NiCd. Plus, with no cadmium are also better for the environment.

Lithium battery – Often used in cameras and high-tech equipment because of their ability to deliver high currents as well as having a long life.

Lithium-ion battery – found in laptops and mobile phones, a light battery that will store a lot of energy and is very powerful. It has no memory effect.

Lead-acid battery – Used in cars, with lead and lead-oxide electrodes and a very strong acidic electrolyte. Car batteries are rather useful because they have a reversible reaction – as the battery gets going, the lead re-forms on the plates in the battery unit, and so they can be used over and over again.

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23 May 2010
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