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Batteries

January 15, 2009 by  


diff 1-12-09

In electronics, a battery or voltaic cell is a combination of one or more electrochemical Galvanic cells which store chemical energy that can be converted into electric potential energy, creating electricity. Since the invention of the first Voltaic pile in 1800 by Alessandro Volta, the battery has become a common power source for many household and industrial applications, and is now a multi-billion dollar industry.

The name “battery” was coined by Benjamin Franklin for an arrangement of multiple Leyden jars (an early type of capacitor) after a battery of cannon. Common usage has evolved to (inaccurately) include a single electrical cell in the definition.

In 1791, Luigi Galvani published a report on “animal electricity.” He created an electric circuit consisting of two different metals, with one touching a frog’s leg and the other touching both the leg and the first metal, thus closing the circuit. In modern terms, the frog’s leg served as both the electrolyte and the sensor, and the metals served as electrodes. He noticed that even though the frog was dead, its legs would twitch when he touched them with the metals.

Within a year, Volta realized the frog’s moist tissues could be replaced by cardboard soaked in salt water, and the frog’s muscular response could be replaced by another form of electrical detection. He already had studied the electrostatic phenomenon of capacitance, which required measurements of electric charge and of electrical potential (“tension”). Building on this experience, Volta was able to detect electric current through his system, also called a Galvanic cell.

In 1800, Volta invented the battery by placing many voltaic cells in series, literally piling them one above the other. This Voltaic pile gave a greatly enhanced net emf for the combination, with a voltage of about 50 volts for a 32-cell pile. In many parts of Europe batteries are still called piles.

Volta did not appreciate that the voltage was due to chemical reactions. He thought that his cells were an inexhaustible source of energy, and that the associated chemical effects (e.g. corrosion) were a mere nuisance, rather than an unavoidable consequence of their operation, as Michael Faraday showed in classic studies that yielded the names anions and cations and anode and cathode (1834). According to Faraday, cations (positively charged ions) are attracted to the cathode, and anions (negatively charged ions) are attracted to the anode.

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