Battery (electricity)
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- For other uses, see battery (disambiguation).
Template:Unreferenced Image:Four AA batteries.jpg In science and technology, a battery is a device that stores chemical energy and makes it available in an electrical form. Batteries consist of electrochemical devices such as one or more galvanic cells, fuel cells or flow cells. The earliest known artifacts that may have been batteries are the Baghdad Batteries, from some time between 250 BCE and 640 CE. The modern development of batteries started with the Voltaic pile developed by the Italian physicist Alessandro Volta in 1800. The worldwide battery industry generates US$48 billion in sales annually (2005 estimate).
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Cell vs. battery
Strictly, an electrical "battery" is an interconnected array of one or more similar voltaic cells ("cells"). 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. For example, a hand lamp (flashlight) (torch) is said to take one or more "batteries" even though they may be D cells. A car battery is a true "battery" because it uses multiple cells -- here, six 2 V lead-acid cells -- in series. Multiple batteries or cells may also be referred to as a battery pack, such as a set of multi-cell 12 V batteries in an electric vehicle.
Electrical component
Image:Battery symbols and circuit.png
The cells in a battery can be connected in parallel, series, or in 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). 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 parallel types, the energy stored in the battery is equal to the sum of the energies stored in all the cells.
A battery can be simply 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 voltage drop across its internal resistance increases, so the voltage at its terminals decreases, and the battery's ability to deliver power to the load decreases.
Battery concepts
Here is some heavy-duty information about voltaic cells, the building blocks of batteries. In the figure (above, on the left) the battery consists of two voltaic cells in series. The positive (negative) terminals (electrodes) are the longer (shorter) lines. Real voltaic cells have ion-carrying electrolyte, made of solid or liquid, separating their terminals. Thus their terminals are not in direct electrical contact. The figure above shows no line connecting the negative terminal of the top cell to the positive terminal of the bottom cell, but in a real cell they would be in direct electrical contact.
The electrolyte contains ions that can react with chemicals in the electrode. Chemical energy is converted into electrical energy by chemical reactions that transfer charge between the electrode and the electrolyte at their interface. Such reactions are called Faradaic, and are responsible for current flow through the cell. Ordinary, non-charge-transferring (non-Faradaic) reactions also occur at the electrode-electrolyte interfaces. Non-faradaic reactions are one reason that voltaic cells (particularly the lead-acid cell of ordinary car batteries) "run down" when sitting unused.
Around 1800 Volta studied, for many different types of voltaic cell, the effect of different electrodes on the net electromotive force (emf) of the cell, Ε. (Emf is equivalent to what was called the internal voltage source in the previous section.) He showed that Ε is the difference of the emfs Ε1 and Ε2 associated with the two electrolyte-electrode interfaces. Hence identical electrodes yield Ε=0 (zero emf). Volta did not appreciate that the emf 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, as Faraday showed around 1830, an unavoidable by-product of their operation.
Electromotive force (emf) is measured in units of volts; therefore the word "force" is a misnomer. Voltaic cells, and batteries of voltaic cells, are normally rated in terms of volts. The voltage across the terminals of a battery is known as the terminal voltage. The terminal voltage of a battery that is not discharging equals its emf. The terminal voltage of a battery that is discharging (charging) is less than (greater than) the emf.
Most voltaic cells are only rated at 1.5 or so volts because of the limitations to how much electrical energy the chemical reactions can provide. Because of the relatively large energy release of Li compounds, Li cells can provide as many as 3 or more volts. This large energy release can be a hazard.
The conventional model for a voltaic cell, as drawn above, has the internal resistance drawn outside the cell. This is a correct Thevenin equivalent for circuit applications, but it oversimplifies the chemistry and physics. In a more accurate (and more complex) model, a voltaic cell can be thought of as two electrical pumps, one at each terminal (the faradaic reactions at the corresponding electrode-electrolyte interfaces), separated by an internal resistance largely due to the electrolyte. Even this is an oversimplification, since it cannot explain why the behavior of a voltaic cell depends strongly on its rate of discharge. For example, it is well-known that a cell that is discharged rapidly (but incompletely) will recover spontaneously after a waiting time, but a cell that is discharged slowly (but completely) will not recover spontaneously.
The simplest characterization of a battery would give its emf (voltage), its internal resistance, and its "charge", or capacity. In principle, the energy stored by a battery equals the product of its emf and its capacity.
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. The more electrolyte and electrode material in the cell, the greater the capacity of the cell. Thus a tiny AAA cell has much less capacity than a much larger D cell, even if both rely on the same chemical reactions (e.g. alkaline cells), which produce the same terminal voltage. Because of the chemical reactions within the cells, the capacity of a battery depends on the discharge conditions such as the magnitude of the current, the duration of the current, the allowable terminal voltage of the battery, temperature, and other factors.
Battery manufacturers use a standard method to determine how to rate their batteries. The battery is discharged at a constant rate of current over a fixed period of time, such as 10 hours or 20 hours, down to a set terminal voltage per cell. So a 100 ampere-hour battery is rated to provide 5 A for 20 hours at room temperature. The efficiency of a battery is different at different discharge rates. When discharging at low rate, the battery's energy is delivered more efficiently than at higher discharge rates. This is Peukert's Law.
Battery lifetime
Disposable alkaline batteries are designed to be used only once. Even if never taken out of the original package, disposable (or "primary") batteries can lose two to twenty-five percent of their original charge every year. This rate depending significantly on temperature, since typically chemical reactions proceed more rapidly as the temperature is raised. This is known as the "self discharge" rate and is due to non-faradaic (non-current-producing) chemical reactions, which occur within the cell even if no load is applied to it.
Until relatively recently, storing batteries at cool temperatures (such as in the refrigerator) could significantly reduce the rate of these side (non-faradaic) reactions and thus extend the storage life of the battery. However, these side reactions have now been reduced to a level where modern batteries need only be stored in a dry place and at normal room temperatures. Some brands of batteries (like Duracell or Energizer) will provide dependable long life even after 5 years of storage under these conditions.
Extreme temperatures also reduce battery performance.
Some information on caring and disposing of alkaline batteries can be found here and here.
Rechargeable batteries self-discharge more rapidly than disposable alkaline batteries. In fact, they can self-discharge up to three percent a day (again, depending on temperature). Due to their poor shelf life, they shouldn't be left in a drawer and then relied upon to power a flashlight or a small radio in an emergency. For this reason, it’s a good idea to keep a few alkaline batteries on hand. Ni-Cd Batteries are almost always "dead" when you get them, and must be charged before first use.
Most Ni-MH batteries can be recharged 500-1000 times whereas Ni-Cd batteries can only be recharged about 400 times.
Special "reserve" batteries intended for long storage in emergency equipment or munitions keep the electrolyte of the battery separate from the plates until the battery is activated, allowing the cells to be filled with the electrolyte. Shelf times for such batteries can be years or decades. However, their construction is more expensive than more common forms.
Terms used for automobile battery power ratings
See Car battery
Battery explosion
Under extreme conditions, certain types of batteries can explode. A battery explosion is usually caused by the misuse or malfunction of a battery (such as the recharging of a non-rechargeable battery or shorting a car battery).
With car batteries, explosions are most likely to occur when a short circuit generates very large currents. 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. In addition, car batteries liberate hydrogen when they are overcharged (because of electrolysis of the water in the electrolyte). Normally the amount of overcharging is very small and so is the amount of explosive gas developed, and the gas dissipates quickly. However, when "jumping" a car battery, the high current can cause the rapid release of large volumes of hydrogen, which could be ignited by a spark nearby (for example, when removing the jumper cables).
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.
Common battery types
Rechargeable and disposable 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. Primary cells can be recharged with varying degrees of success using a specialised charging technique called periodic current reversal which is a form of biased AC (i.e. alternating current with a DC offset) However battery manufacturers don't recommend attempting to recharge primary cells (cynics claim this is for commercial motives) and claim that conventional DC charging of primary cells can present dangers of leakage, overheating and even explosion.
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 reverses the chemical reactions that occur in use. 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 hydrogen gas which is 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 for a short period, and has a peak current output that varies from 450 to 1100 amperes. The battery's electrolyte includes 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 (NiCd), nickel metal hydride (NiMH), and lithium-ion (Li-Ion) cells.
Disposable
Non-rechargeable - sometimes called "primary cells".
- Zinc-carbon battery - low cost - used in light drain applications
- Zinc-chloride battery - similar to zinc carbon but slightly longer life
- Alkaline battery - alkaline/manganese "long life" batteries widely used in both light drain and heavy drain applications
- Silver-oxide battery - commonly used in hearing aids
- Lithium battery - commonly used in digital cameras. Sometimes used in watches and computer clocks. Very long life (up to ten years in wristwatches) and capable of delivering high currents but expensive
- Mercury battery - commonly used in digital watches
- Zinc-air battery - commonly used in hearing aids
Rechargeable
Also known as secondary batteries or accumulators.
- Lead-acid battery - commonly used in vehicles, alarm systems and uninterruptible power supplies. Used to be used as a "A" or "wet" battery in valve/vacuum tube radio sets.
- Lithium ion battery
- Lithium ion polymer battery
- NaS battery
- Nickel metal hydride battery
- Nickel-cadmium battery - used in many domestic applications but being superseded by Li-Ion and Ni-MH types
- Sodium-metal chloride battery
- Nickel-zinc battery
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 (lemon, etc.) 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, due to the need for frequent replacement of the fruit or vegetable.
Traction batteries
Traction batteries (secondary batteries or accumulators) are designed to provide power to move a vehicle, such as an electric car or tow motor. A major design consideration is power to weight ratio since the vehicle must carry the battery. To prevent spilling, the electrolyte in traction batteries is gelled. The electrolyte may also be embedded in a glass wool which is wound so that the cells have a round cross-sectional area (AGM-type). The following types are also in use[1]:
- Zebra NiNaCl (or NaNiCl) battery operating at 270 °C requiring cooling in case of temperature excursions
- NiZn battery (higher cell voltage 1.6 V and thus 25% increased specific energy, very short lifespan)
Lithium-ion batteries are now pushing out NiMh-technology in the sector while for low investment costs the lead-acid technology remains in the leading role[2].
See also: Battery pack
Flow batteries
Flow batteries are a special class of battery where additional quantities of electrolyte are stored outside the main power cell of the battery, and circulated through it by pumps or by movement. Flow batteries can have extremely large capacities and are used in marine applications and are gaining popularity in grid energy storage applications.
Zinc-bromine and vanadium redox batteries are typical examples of commercially-available flow batteries.
Common battery sizes
Image:Nine Volt Battery.JPG Disposable cells and some rechargeable 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 include the A-series (A, AA, AAA, AAAA), B, C, D, F, G, J, and N, 3R12, 4R25 and variants, PP3 and PP9, and the lantern 996 and PC926. These and less common types are included in the list of battery sizes appearing in the following section (the list can be opened as a separate page as well).
A good cross-reference of different manufacturer's battery and cell designations can be found here [3] and here [4].
History
There is some evidence—in the form of the Baghdad Batteries from some time between 250 BCE and 640 CE (while Baghdad was under Parthian and Sassanid dynasties of ancient Persia) of galvanic cells having been used in ancient times. Such ancient knowledge in the history of electricity bears no known continuous relationship to the development of modern batteries. The hypothesis that these devices had an electrical function, while plausible, remains unproven, as with devices discovered in Egyptian digs that are alleged to be batteries as well.
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 the Italian physicist 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). The discoverer of biological electricity, Luigi Galvani, researched the same effect with two pieces of the same metal exposed to salt water.
The scientific community at this time called this battery a pile, accumulator, because it held charge, or artificial electrical organ.
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. Some early battery researchers called the Daniell cell 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. 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 Planté 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 an 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 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 the 1950s, Ruben improved the alkaline manganese battery. 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.
Environmental considerations
Since their development over 250 years ago, batteries have remained among the most expensive energy sources, and their manufacture consumes many valuable resources and often involves hazardous chemicals. For this reason many areas now have battery recycling services available to recover some of the more toxic (and sometimes valuable) materials from used batteries.
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.
Future cell management is able to condition one cell while the others are in operation, so a much longer operation is possible.
There is currently research into ultra-high voltage capacitors, which may end up replacing batteries.
See also
People/inventors
- John Frederic Daniell
- Thomas Edison
- Michael Faraday
- Luigi Galvani
- Moritz von Jacobi
- Georges Leclanché
- Slavoljub Penkala
- Nikola Tesla
- Alessandro Volta
Related electrical topics
- Contact tension
- Potential difference
- Electric vehicle
- Electrical efficiency
- Electricity
- Electrochemical cell
- Electrochemical potential
- Electrochemistry
- Electromotive force
- Electroplating
- Energy storage
- Flow battery
- Lead-acid battery
- Local battery
- Power supply
- Direct current
- Solar power
- Renewable energy
- Peukert's Law
Related electronics concepts
- Series and parallel circuits
- Secondary cell
- Electrode
- Electrolytic capacitor
- Fuel cell
- Galvanic cell
- Ignition system
- Lemon battery
- Jump start
- Lantern
- Flywheel energy storage
- Rechargeable battery
- Maximum power theorem
- Nernst equation
- Superconducting magnetic energy storage
- Grid energy storage
Chemicals used in construction
- Sulfur
- Mercury
- Sulfuric acid
- Zinc
- Ammonium chloride
- Antimony
- Cadmium
- Silver
- Nickel
- Nickel metal hydride
- Lithium
- Hydride
- Cobalt
- Manganese
- Nitroglycerin
- Rubidium
- Thionyl chloride
- Lead
- Titanium
Related inventions
- Baghdad Battery
- Voltaic pile
- Timeline of invention
- List of inventors
- Smart Battery Data battery warns device when it is going flat.
- Lithium polymer
Other
External links
- RadioShack Guide to Batteries
- Quick Battery Guide For Robot Creators
- Electrochemistry Encyclopedia NONRECHARGEABLE BATTERIES
- Battery Glossary & Terminology
- Battery Technologies - Directory page covering theory, research and development, and market devices that improve the trend toward clean, renewable energy. (FreeEnergyNews)
- The Microturbine, battery technology as "the Next Big Thing" by Fred Hapgood
- Batteries in a Portable World - A Handbook on rechargeable batteries for non-engineers - Has a comprehensive FAQ section on rechargeable batteries
- Battery Timeline - History of batteries, energy and related technologies
- Mobile phone fuel cells coming in 2007 Infoworld July 13, 2005
- "Battery Resources" of PESWiki, the community-built website dealing with alternative and renewable energy solutions
- A Peukert Calculator spreadsheet
- Practical battery knowledge
- Energyorbit battery newsTemplate:Link FA
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