How does a rechargeable battery work?

Written by lauren vork
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How does a rechargeable battery work?

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What Is a Battery?

Whether you're talking about the rechargeable or non-rechargeable variety, all batteries work on the same basic principle: They are essentially a canister of chemicals that produce electricity. Certain chemical reactions do this via the principles of electrochemistry. The most basic electrochemical reactions in batteries entail electrolyte substances (such as acids) causing metals to oxidise.

As the metal oxidises, it gives off electrons; these electrons can also be transferred to another metal in the same electrolyte solution, resulting in electricity as they flow. The positive and negative sides of a battery connect to these two metals, but they are not directly connected to one another (this would be highly dangerous). Instead, electrons flow from the negatively charged side, through a device (which powers it) and into the positively charged side.

Early, simple batteries suspended metal in a liquid electrolyte, such as iodine or salt water. Modern batteries are made with dry or paste electrolyte compounds separating the two pieces of metal in a tube. Most batteries are made up of several such chambers.

Rechargeables

A rechargeable battery is charged by directing a new flow of electrons back into the oxidised metal, which allows the process to begin again. To do this using a standard wall outlet, an adaptor is required. An adaptor is a device that modulates the current from the wall socket into a current of the appropriate strength. This is necessary because, in order for the battery to recharge, the current applied to it must be of the same voltage as the current the battery produces.

One of the oldest and most well-known types of rechargeable batteries is the lead-acid battery found in cars. For lead-acid batteries, the car's alternator is the adaptor, converting gasoline into an electrical charge of the correct voltage to charge the battery.

Materials

The difference between various types of rechargeable batteries, and the difference between rechargeable and non-rechargeable batteries, is in what materials the battery is made of. Technically, all batteries can be recharged, but batteries that are designated as non-rechargeable are made from materials that will cause the outer casing of the battery to dissolve if used repeatedly.

Rechargeable batteries are made from a variety of materials, with new advances being made all the time regarding which types of metals and chemicals will make batteries powerful, lightweight and long-lasting. One such advance is the phasing out of nickel-cadmium rechargeable batteries. The cadmium electrolyte within these batteries would crystallise during the batteries' discharge. These crystals would reform into cadmium during recharge, but only if the battery were fully discharged first (since the crystals deep inside the battery wouldn't otherwise be affected by electrical current). The resulting "memory effect," with rechargeable batteries losing power capacity with each charge, has been a well-known frustration with common rechargeables.

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