What`s Up with Laptop Batteries? - Battery Chemistry
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Batteries depend on chemical reactions, and the reactions must be reversible in order for the battery to be rechargeable. Reversible reactions are just what the name implies, reactions that can be undone or reversed by the application of an external energy source, which is a battery charger in the case of laptop batteries.
The ideal dry battery described above does not actually exist. Most modern batteries rely on the principle of operation of a wet battery, of which a lead-acid car battery is an example.
In part of a wet battery circuit, electrons are transferred by the migration of charged chemical particles called ions that are dissolved in a liquid called an electrolyte. Ions are either positive or negative. Negative ions have an extra electron that they can give up (hence the negative charge) and positive ions can accept an electron.
There are two parts to a wet battery circuit: the wet part and the dry part. The electrons (or charges if you prefer) in a wet battery make a complete circle. In the dry part of the circuit, they flow as electrical current through a conductor like a wire, from the positive terminal (less electronegative) to the negative terminal (more electronegative). In the wet part of the circuit, they are returned by the above described movement of ions from the negative terminal back to the positive terminal. In the case of a car battery, the battery itself is the wet part of the circuit, and the wires between the two battery terminals that supply power to the starter, etc. are the dry part of the circuit.
If the electrons in a wet battery are making a complete circle, why, you ask, does the battery ever need to be recharged? Though this is a bit of an oversimplification, it is because after ions migrate from one pole of the battery to the other, they don't return. They build up until the migration of ions through the electrolyte is blocked and current flow ceases.
A big advantage of batteries that operate on this principle is rechargeability. When current is applied in the reverse direction, the ions either recover the electrons they lost, or they give up the electrons they gained, and they migrate back through the electrolyte solution to their terminal of origin. This restores the battery to its original state before discharge, ready to produce current again.
Modern batteries used in portable devices such as laptops work on the same principle as true wet batteries such as a car battery. They also utilize an electrolyte through which ions travel, but the electrolyte is not a liquid. In some cases, it is a paste or similar material.
Ok, that's enough background. Now let's take a look at real laptop batteries.
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