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Battery (electricity)

     
Four double-A batteries   SEE ALSO: HOW DOES A BATTERY WORK
Four double-A batteries
   

In science and technology, a battery is a device that stores energy and makes it available in an electrical form. Although such storage in an electrostatic form is practical in some specialized uses (in a capacitor), batteries usually consist of electrochemical devices such as one or more galvanic cells or more recently fuel cells, and may in the future use other technologies. The battery industry is worth 2.8 billion dollars annually.

In a technical sense, the distinction may be made between

  • an electrical battery, a device for creating or storing electrical energy composed of several similar (usually identical) cells that are connected together, versus
  • an electrical cell, a single such unit, possibly one cell in a (strict-terminology) battery of multiple cells or possibly the entire device.

That distinction, however, is considered pedantic in most contexts (other than the expression dry cell), and in current English usage it is more common to call a single cell used on its own a battery than a cell.

An example is a double A (AA) battery. Even though most people call it a battery, in reality it is a cell (as are the other lettered designations although one often hears the more-correct "D cell" or "C cell"). A car battery is a true "battery" because it uses multiple cells inside of it that are connected together in series, thus forming a battery. Similarly, a 9-volt battery is a true battery as it must contain more than one cell.

History

There is some evidence—in the form of the Baghdad Batteries from sometime between 250 BC and 640 AD—of galvanic cells having been used in ancient times to electroplate base metal objects with a precious metal. Such ancient knowledge in the history of electricity bears no known continuous relationship to the development of modern batteries. The conjecture that these devices had an electrical function, while plausible, remains unproven.

In 1748, Benjamin Franklin coined the term battery to describe the simple capacitor he experimented with, which was an array of charged glass plates. He adapted the word from its earlier sense meaning a beating, which is what an electric shock from the apparatus felt like. In those days, the entertaining effect of an electric shock was one of the few uses of the technology. Other experimenters made batteries from a number of Leyden jars connected in parallel. The definition was later widened to include an array of electrochemical cells or capacitors. The Voltaic pile was a chemical battery developed by Alessandro Volta in 1800. Volta researched the effects which different metals produced when exposed to salt water. In 1801, Volta demonstrated the Voltaic cell to Napoleon Bonaparte (who later ennobled him for his discoveries). Luigi Galvani researched the same effect with two pieces of the same metal exposed to salt water.

The scientific community at this time called these batteries piles. The battery was called an accumulator, because it held charge, or an artificial electrical organ. Some early researchers over batteries called the device a gravity cell because gravity kept the two sulfates separated. The name crowfoot cell was also commonly used because of the shape of the zinc electrode used in the batteries.

In 1800, William Nicholson and Anthony Carlisle used a battery to decompose water into hydrogen and oxygen. Sir Humphry Davy researched this chemical effect at the same time. Davy researched the decomposition of substances (called electrolysis). In 1813, he constructed a 2,000-plate paired battery in the basement of Britain's Royal Society, covering 889 ft² (83 m²). Through this experiment, Davy deduced that electrolysis was the action in the voltaic pile that produced electricity. In 1820, the British researcher John Frederic Daniell improved the voltaic cell. The Daniell cell consisted of copper and zinc plates and copper and zinc sulfates. It was used to operate telegraphs and doorbells. Between 1832 and 1834, Michael Faraday conducted experiments with a ferrite ring, a galvanometer, and a connected battery. When the battery was connected or disconnected, the galvanometer deflected. Faraday also developed the principle of ionic mobility in chemical reactions of batteries. In 1839, William Robert Grove developed the first fuel cell, which produced electrical energy by combining hydrogen and oxygen. Grove developed another form the electric cell using zinc and platinum electrodes. These electrodes were exposed to two acids separated by a diaphragm.

In the 1860s, Georges Leclanché of France developed a carbon-zinc battery. It was a wet cell, with electrodes plunged into a body of electrolyte fluid. It was rugged, manufactured easily, and had a decent shelf life. An improved version called a dry cell was later made by sealing the cell and changing the fluid electrolyte to a wet paste. The Leclanché cell is a type of primary (non-rechargeable) battery. In the 1860s, Raymond Gaston Plant invented the lead-acid battery. He immersed two thin solid lead plates separated by rubber sheets in a dilute sulfuric acid solution to make a secondary (rechargeable) battery. The original invention had a short shelf life, though. Around 1881, Émile Alphonse Faure, with his colleagues, developed batteries using a mixture of lead oxides for the positive plate electrolyte. These had faster reactions and higher efficiency. In 1878, the air cell battery was developed. In 1897, Nikola Tesla researched a lightweight carbide cell and a oxygen-hydrogen storage cell. In 1898 Nathan Stubblefield received approval for a battery patent (US600457): this electrolytic coil patent is referred to as an "earth battery".

In 1900, Thomas Edison developed the nickel storage battery. In 1905, Edison developed the nickel-iron battery. Like all electrochemical cells, Edison's produced a current of electrons that flowed only in one direction, known as direct current. In World War II, Samuel Ruben and Philip Rogers Mallory developed the mercury cell. In the 1950s, Russell S. Ohl developed a wafer of silicon that produced free electrons. In the 1950s, Ruben improved the alkaline manganese battery. In 1954, Gerald L. Pearson, Daryl M. Chapin, and Calvin S. Fuller produced an array of several such wafers, making the first solar battery or solar cell. In 1956, Francis Thomas Bacon developed the hydrogen-oxygen fuel cell. In 1959, Lewis Urry developed the small alkaline battery at the Eveready Battery Company laboratory in Parma, Ohio. In the 1960s, German researchers invented a gel-type electrolyte lead-acid battery. Duracell was formed in 1964.

Homemade cells

Almost any liquid or moist object that has enough ions to be electrically conductive can serve as the electrolyte for a cell. As a novelty or science demonstration, it is possible to insert two electrodes into a lemon, potato, glass of soft drink, etc. and generate small amounts of electricity. As of 2005, "two-potato clocks" are widely available in hobby and toy stores; they consist of a pair of cells, each consisting of a potato with two electrodes inserted into it, wired in series to form a battery with enough voltage to power a digital clock. Homemade cells of this kind are of no real practical use, because they produce far less current—and cost far more per unit of energy generated—than commercial cells.

The future

Initial research indicates that nanotechnology batteries employing carbon nanotubes will have twice the life of traditional modern batteries.

A new form of battery is in development called Power Paper. This thin, flexible battery comes in the form of ink cells which can be printed on to virtually any surface and produce power.

Electrical component

Circuit symbol for a battery (+ and - signs are optional)
Circuit symbol for a battery (+ and - signs are optional)

The cells in a battery can be connected in parallel or in series, or both. A parallel combination of cells has the same voltage as a single cell, but can supply a higher current (the sum of the currents from all the cells). On the other hand, a series combination has the same current rating as a single cell but its voltage is the sum of the voltages of all the cells. Most practical electrochemical batteries, such as 9 volt flashlight (torch) batteries and 12 V automobile (car) batteries, have a series structure. Parallel arrangements suffer from the problem that, if one cell discharges faster than its neighbour, current will flow from the full cell to the empty cell, wasting power and possibly causing overheating. Even worse, if one cell becomes short-circuited due to an internal fault, its neighbour will be forced to discharge its maximum current into the faulty cell, leading to overheating and possibly explosion. Cells in parallel are therefore usually fitted with an electronic circuit to protect them against these problems. In both series and paralllel types, the energy stored in the battery is equal to the sum of the energies stored in all the cells.

A battery can be modelled as a perfect voltage source (i.e. one with zero internal resistance) in series with a resistor. The voltage source depends mainly on the chemistry of the battery, not on whether it is empty or full. When a battery runs down, its internal resistance increases. When the battery is connected to a load (e.g. a light bulb), which has its own resistance, the resulting voltage across the load depends on the ratio of the battery's internal resistance to the resistance of the load. When the battery is fresh, its internal resistance is low, so the voltage across the load is almost equal to that of the battery's internal voltage source. As the battery runs down and its internal resistance increases, the proportion of its internal voltage that gets through the internal resistance to appear at the load gets smaller, so the battery's ability to deliver power to the load decreases.

Common battery types

various batteries
various batteries

From a user's viewpoint, at least, batteries can be generally divided into two main types - rechargeable and non-rechargeable (disposable). Each is in wide usage.

Disposable batteries, also called primary cells, are intended to be used once, until the chemical changes that induce the electrical current supply are complete, at which point the battery is discarded. These are most commonly used in smaller, portable devices with either low current drain, only used intermittently, or used well away from an alternative power source. See also: waste.

By contrast, rechargeable batteries or secondary cells can be re-charged after they have been drained. This is done by applying externally supplied electrical current which causes the chemical changes that occur in use to be reversed. Devices to supply the appropriate current are called chargers or rechargers.

The oldest form of rechargeable battery still in modern usage is the wet cell lead-acid battery. This battery is notable in that it contains a liquid in an unsealed container, requiring that the battery be kept upright and the area be well-ventilated to deal with the explosive oxygen and hydrogen gases which are vented by these batteries during overcharging. The lead-acid battery is also very heavy for the amount of electrical energy it can supply. Despite this, its low manufacturing cost and its high surge current levels make its use common where the weight and ease of handling are not concerns.

A common form of lead-acid battery is the modern car battery. This can deliver about 10,000 watts of power at a nominal 12 volts (although the true open-circuit voltage is closer to 13.7 V) and has a peak current output that varies from 450 to 1100 amperes. The battery's electrolyte is sulfuric acid, which can cause serious injury if splashed on the skin or eyes.

A more expensive type of lead-acid battery called a gel battery (or "gel cell") contains a semi-solid electrolyte to prevent spillage. More portable rechargeable batteries include several "dry cell" types, which are sealed units and are therefore useful in appliances like mobile phones and laptops. Cells of this type (in order of increasing power density and cost) include nickel-cadmium (nicad or NiCd), nickel metal hydride (NiMH), and lithium-ion (Li-Ion) cells.

Common battery sizes

Disposable cells come in a number of standard sizes, so the same battery type can be used in a wide variety of appliances. Some of the major types used in portable appliances are listed below:

US IEC ANSI Other Shape Voltage
N LR1 910A lady cylinder L 30.2 mm, D 12 mm 1.5 V
AAAA   25A MN2500 cylinder L 42 mm, D 8 mm 1.5 V
AAA LR03 24A R03,MN2400, AM4,UM4,HP16,micro cylinder L 44.5 mm, D 10.5 mm 1.5 V
AA LR6 15A R6,MN1500, AM3,UM3,HP7,mignon cylinder L 50 mm, D 14.2 mm 1.5 V
A     filament supply in early radio receivers rectangular prism various sizes.
cylinder L 50 mm, D 17 mm
1.5 V, 6 V
B     plate supply in early radio receivers rectangular prism various sizes, often with taps. 45 V, 60 V, 90 V, etc.
C     grid bias supply in early radio receivers rectangular prism various sizes, often with several taps. 4.5 V, 6 V, 9 V, etc.
C LR14 14A R14,UM2,MN1400,HP11,baby cylinder L 43 mm, D 23 mm 1.5 V
D LR20 13A R20,MN1300,UM1,HP2,mono cylinder L 58 mm, D 33 mm 1.5 V
F       cylinder L 87 mm, D 32 mm 1.5 V
G       cylinder L 105 mm, D 32 mm 1.5 V
J       cylinder L 150 mm, D 32 mm 1.5 V
  3R12   GP312S rectangular prism 67 mm × 62 mm × 22 mm 4.5 V
      lantern,996 rectangular prism 68 mm square × 115 mm 6 V (note)
PP3 6LR61 1604A 6F22,6R61,MN1604 rectangular prism 48 mm × 25 mm × 15mm 9 V (note)
PP9 6F100 1603   rectangular prism 51.6mm × 65.1 mm × 80.2 mm high 9 V (note)
  4R25X 908 MN908 square prism 110 mm high × 67.7 mm square, spring terminals 6 V (note)
  4R25 915   square prism 110 mm high × 67.7 mm square, screw terminals 6 V (note)
  4LR25-2 918A MN918 rectangular prism 127 mm × 136.5 mm × 73 mm high, screw terminals 6 V (note)
      PC926 rectangular prism 127 mm × 136.5 mm × 73 mm high, screw terminals 12 V (note)

Note: 6 V, 9 V, and 12 V batteries are commonly made using multiple 1.5 V cells placed in series. See electrochemical cell.

The relevant European standard is IEC 60086-1 Primary batteries - Part 1: General (BS397 in the UK).

The relevant US standard is ANSI C18.1 American National Standard for Dry Cells and Batteries-Specifications.

An extensive series of articles on many aspects of batteries and their use in portable equipment is available at Buchmann.ca (http://www.buchmann.ca/).

Summary

Disposable

Rechargeable

Battery capacity

The capacity of a battery to store charge is often expressed in ampere hours (1 A·h = 3600 coulombs). If a battery can provide one ampere (1 A) of current (flow) for one hour, it has a real-world capacity of 1 A·h. If it can provide 1 A for 100 hours, its capacity is 100 A·h. Likewise, 20 A for 2 hours equals 40 A·h capacity. But...

While a battery that can deliver 10 A for 10 hours can be said to have a capacity of 100 A·h, that is not how the rating is determined by the manufacturers. A 100 A·h rated battery most likely will not deliver 10 A for 10 hours. Battery manufacturers use a standard method to determine how to rate their batteries. Their rating is based on tests performed over 20 hours with a discharge rate of 1/20 (5%) of the expected capacity of the battery. So a 100 ampere-hour battery is rated to provide 5 A for 20 hours. The efficiency of a battery is different at different discharge rates. When discharging at 1/20 of their capacity, batteries are more efficient than at higher discharge rates.

To calculate the 5% discharge rate of a battery, take the manufacturer's ampere-hour rating and divide it by 20. For example, you have a AA cell rated at 1300 mA h (milliampere hours). The 5% discharge rate from which this rating was derived would be 1300 mA·h / 20 h = 65 mA.

Battery explosion

Under extreme conditions, certain types of batteries can explode violently. A battery explosion is usually caused by the misuse or malfunction of a battery (such as the recharging of a non-rechargable battery or shorting a car battery).

With car batteries, explosions are most likely to occur when a short circuit generates currents of very high magnitude. A short circuit malfunction in a battery placed in parallel with other batteries ("jumped") can cause its neighbour to discharge its maximum current into the faulty cell, leading to overheating and possible explosion.

When a non-rechargeable battery is recharged at a high rate, an explosive gas mixture of hydrogen and oxygen may be produced faster than it can escape from within the walls of the battery, leading to pressure build-up and a possible explosion. In extreme cases, the battery acid may spray violently from the casing of the battery and cause injury.

Additionally, disposing of a battery in fire may cause an explosion as steam builds up within the sealed case of the battery.

Overcharging, which is charging a battery beyond its electrical capacity, can also lead to a battery explosion, leakage, or irreversible damage to the battery. It may also cause damage to the charger or device in which the overcharged battery is later used.

 

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