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How power became portable: An introduction to battery technology

how batteries work battery head credit borys shevchuk
Borys Shevchuk / 123RF

The modern world, in all its grandeur and complexity, runs off a shockingly primal force, one that has been flowing through human bodies long before the first motor was built. Electricity, that same force that has kept human hearts beating for as long as there have been human hearts to beat, today flows through the veins of civilization, powering the skyscrapers we work in and the phones in our pockets.

Although the great producers of electricity, colossi like the Hoover Dam, may be the most viscerally impressive, human mastery of electrical currents is perhaps most impressive in the form of batteries. Some small enough to sit on the tip of a finger, batteries power many of the devices we use every day: phones, laptops, flashlights, watches. They have been an omnipresent part of life for decades now, but how many of us know how they work?

Beneath their simple exteriors, a simple mechanism

A typical alkaline battery will be familiar to many people, at least from the outside. Generally encased in a metal cylinder, the battery has two ends marked as + (positive) and – (negative). The two ends of a battery are terminals, connected to electrodes within the battery: the positive end connects to a cathode, while the negative end connects to an anode. A separator inside the battery keeps the two from touching, while allowing electricity to flow between them. Between the two ends is an electrolyte paste, a substance that allows for the flow of electrical current.

anatomy of battery

Electrons naturally want to flow from the negative end (where there are excess electrons) to the positive end (where there are open spaces for electrons), however they cannot do so because the separator blocks their path. By connecting the positive and negative ends of the party, a circuit is formed that allows electrical current to flow.

circuit diagram

When a battery is plugged into a device, such as a flashlight or remote, a circuit is established and chemical reactions occur in the anode and cathode. In the anode, an oxidation reaction occurs, where ions combine with the anode and release electrons. In the cathode, a reduction reaction occurs, with ions and electrons forming compounds. In these oxidation-reduction reactions, electrons are flowing from the negatively charged anode to the positively charged cathode.

In an alkaline battery, the anode is made of zinc, while the cathode is manganese dioxide. The electrodes in these batteries erode over time. Rechargeable batteries are usually made of lithium-ion. When plugged in to recharge, the flow of electricity reverses, returning the anode and cathode to their original states.

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