Tim suggested today that batteries are small blessings. We do take them for granted until they give out. Even though I know generally how they work, they are mysterious, locking in all that electricity, just waiting until I press a button to release it. Especially mysterious are the little flat disk ones that look very much like a button or a silver pill.
Our car runs on batteries part of the time - it is a Prius and gets into stealth mode, ghosting along almost silently on battery power alone. It cleverly recharges its own batteries. We leave for the future worrying about what happens when its batteries give out.
Regular car batteries are not so different from those invented by Alessandro Volta in 1800. They are containers with series of plates of lead and lead dioxide immersed in a sulfuric acid solution. The acid breaks down the metal plates, or electrodes, into positive- and negatively-charged ions, which migrate to the oppositely-charged plates. An electrical potential, in effect a driving force, develops between the negative and positive plates. Connecting them through a device allows a flow of electrons (negatively-charged) toward the positively-charged electrodes. Mind you, the electricity doesn't actually flow out of the battery to the device; the charge provides a push to electrons already in the wire, which move only a tiny distance. Confusing? Yes, well I think I am stating all this correctly, but am not entirely sure! On top of this, these batteries can be recharged by creating a driving force in the opposite direction with an electric motor (alternator in modern cars). The lead plates eventually corrode away. Then we have to replace our battery.
The small "dry cell" batteries are even more mysterious, although the principle is the same. Alkaline batteries have two metals, usually zinc and manganese dioxide for the negative and positive electrodes, respectively. They are separated by a gel of strongly alkaline material (as opposed to acid in the car battery). This alkaline material causes the chemical reaction between the metals to take place, causing charged ions to cluster to their oppositely-charged electrode.
Other kinds of batteries use more exotic metals for their electrode and exotic materials for their electrolytes. For instance, we hear about nickle metal hydride batteries and lithium-ion. Battery development is a very high priority for researchers because of the need for long-lived batteries for portable computers and phones and of energy-dense ones (that is, able to produce a lot of electricity for their weight) for electric cars.
Anyone still reading this is a patient soul indeed! Let's appreciate our little batteries for the marvels they really are.
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As I wrote to a friend today, I got in over my head with this. "Take anodes and cathodes. I can never remember which is which. Top that with the fact that battery circuits used to be taught backwards - ie, that the "electricity" came out of the positive terminal and went into the negative, which is backwards to what happens. Then there is the whole business that the electrons aren't really coursing through the wire like water through a pipe, just nudging one another. What I was taught eons ago was in fact an incorrect model of what actually happens. I also don't really understand the chemistry - how the acid or base rips charged particles off the metal electrodes and causes them to build up here or there.
ReplyDeleteAll in all, shouldn't have gone there. However... batteries are still marvelous things!!"