Scientists and engineers have sent men to the moon and unraveled the genetic code. Why is it that they have yet to come up with a laptop battery that lasts longer than a few hours? We will attempt to answer that question and more, in this article on the state of laptop battery technology.
Background
Electrochemistry
Chemical reactions are what make batteries work, so first, let's learn a little bit about electrochemistry to help us better understand batteries. Don't worry, you'll know everything you need to know about it by the end of the next few paragraphs.
We know that batteries are sources of electricity, but what is electricity? Some purists would dispute this definition, but you won't go wrong if you think of electricity as electrons. You may recall from chemistry class that electrons are those little things that orbit around the nucleus of an atom. Moving electrons are electrical current, and electrons sitting still are electrical charge. The job of a battery is to make electrons move, thereby producing electrical current.
Electronegativity
The electrochemical reactions that take place inside a battery depend on electronegativity, so we will learn a bit about it.
Electronegativity is a measure of how much attraction a substance has for electrons. A highly electronegative substance will attempt to pull electrons from a less electronegative substance. An example of this is the rusting of iron when exposed to air. In this reaction, oxygen, one of the most electronegative elements, steals electrons from the less electronegative element, iron, causing it to corrode.
Normally, less electronegative substances are protected from more electronegative substances by the lack of any way for electrons to pass between them. The situation changes when a wire is connected between the more electronegative substance and the less electronegative substance. Since wire is a conductor, there is now a means for electrons to pass between the two. The hungry bully that is the more electronegative substance will suck electrons from the poor, less electronegative substance, causing electrical current to flow through the wire, until either its hunger for electrons is satiated, or the less electronegative substance has no more electrons that can be stolen.
If this scenario featured a battery, which it describes, the battery would now be discharged.
The reaction between the two substances of differing electronegativity will only go so far before the buildup of electrons on one side, and the dearth of electrons (buildup of positive charge) on the other side causes it to stop. How long the reaction can go varies with the different substances used for the anode and cathode. Therein lies the fundamental answer to why longer battery life has been so difficult to achieve. It is because scientists and engineers are limited to the elements that nature provides, to utilize as battery components (forget rare elements produced in nuclear reactors), and there is a limit to the amount of electrons that any of these elements or compounds created from the elements can accept or donate.
The following diagram illustrates how a simple ideal battery works (the little e's are electrons). Note that in the diagram, electricity is shown as flowing in the opposite direction of the electrons. This is because electrical current or electricity is defined as the net flow of positive charge. In a metal such as copper, commonly used for wires, the nuclei of the atoms, which contain the positive charges, are locked in fixed positions, so it is really more accurate to describe the flow of electricity in a metal as the flow of electrons, but electricity flowing from negative to positive is the convention.
You can see in the diagram that the electrons are becoming more scarce on the less electronegative (positive) pole, which is referred to as the cathode, and are building up on the more electronegative (negative) pole, which is referred to as the anode. If this were a real battery, it would mean that it is becoming discharged.
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