how does a battery produce electricity

8/8/2019 How Does a Battery Produce Electricity

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How does a battery produce electricity?

An electrifying topic.

A battery, by definition, consists of a group of two or more primary or secondary battery

cells, which convert chemical energy into electrical energy. A portion of the chemical energya cell produces is transformed into heat, and a portion into an electric current.

Primary battery cells can only be renewed during down time, when they replenish theirchemicals. When one reach for his or her emergency flashlight, which contains a type ofprimary cell named an ordinary cell, and it fails to light up, one falls victim of this veryprinciple.

Each and every primary cell uses various chemicals, and contains electrodes and anelectrolyte, a liquid. Electrodes, a.k.a. "cell elements," consist of either two different metals,or one metal and carbon. Element number one, the cathode, is primarily zinc. Elementnumber two, the anode, is primarily carbon.

A chemical action sets the electrons free, when it triggers the cathode slowly to dissolve intothe liquid electrolyte. A circuit provides the escape route for the newly paroled electrons,and they rush down the hatch in the form of an electric current. Unfortunately, theirfreedom is short-lived, because, once an electrical conductor is connected to the twoelements, the current flowing through it is recaptured as electricity.

Secondary battery cells merit less discussion, as they automatically recharge, when anelectric current is injected through them. Primary examples of a secondary battery cells arethe storage cells used to start, or not to start, our car batteries. Because a storage batterydoes not actually store electricity, it instills in one a false sense of security. One is welladvised to carry jumper cables in our cars, for those times when, much to ones chagrin, thebattery fails to start.

The misnomered "storage battery," draws its power from chemical charges. Inside a storagebattery, one finds a set of plates made of metallic lead, and a set made of lead peroxide.When both sets of plates are immersed in sulphuric acid, they undergo a chemical change,which transforms them into lead sulphate, which in turn produces the electrical current inthe storage battery, which does not store. A word of caution...do not try this one at home!

Does a car battery circulate electricity evenwhen the car is off?


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with batteries isnt their expense fuel cells cost orders of magnitude more than batteriesdo. Moreover, the problem with batteries isnt their efficiency storing electricity abattery will discharge to an electric motor 90% of the electricity used to charge it. If thatsame electricity were used to electrolyse hydrogen, at least 30% of the energy would belost, and if that hydrogen were then ran through an on-board fuel cell to power an electric

motor, another 40% of the energy would be lost. That is, if you put 100 kilowatt-hoursinto a battery, youll get 90 kilowatt-hours back to power your motor. If on the otherhand, you put 100 kilowatt-hours into electrolysing hydrogen, then in-turn convert thathydrogen back into electricity to power your motor, you will only have 42 kilowatt-hoursavailable from your original 100. For storing electricity, a battery is more than twice asefficient as a fuel cell.

SERIES HYBRID CARADVANCED PROTOTYPE (top view)

Four powerful in-wheel motorsindependent 360 degree steering(elec=R, batt=G, diesel=O)

So why dont we use all this technology to manufacture cars powered exclusively by

batteries? The answer is batteries weigh too much, but this is changing. Typical lead-acidbatteries get about 60 watt-hours to the kilogram. The newer nickel metal hydridebatteries used to power hybrid cars get up to 120 watt-hours to the kilogram. Still furtheradvanced lithium-ion batteries are approaching 200 watt-hours to the kilogram. Thismeans that whatever range an electric car may have had using lead-acid batteries can nowbe doubled, or even tripled.Advances in battery technology spurred by hybrid vehicle development may lead to thehybrid car not giving way to a fuel cell car, but, at least for many applications, to a 100%electric car. It isnt like this hasnt been tried before. General Motors EV-1 is alegendary example of an electric car that was ahead of its time. This vehicle had a rangeof 100 miles on a charge, and it had a top speed on 180 MPH! The car was equipped with

a governor to keep the drivers from going that fast. When GM made the heartbreakingdecision to discontinue the EV-1, it looked like electric cars would go the way of thesteam locomotive. But with advances in battery technology, electric cars are making acomeback.Today there are hybrid car owners who are making their hybrid cars capable of beingplugged in. Other tinkerers are adding additional batteries to their hybrid cars. But whynot go 100% electric? Just think no twin drive train for the gas engine and the electricmotor, no transmission, and a far less complex power-management system. Why


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wouldnt someone want to just come home and plug their car in? No more gas stations.No more expensive gas.

HOW MUCH WOULD IT COST TO DRIVE A 100% ELECTRIC CAR?

At $.06 US per KWh, a battery-powered car costs $.02 per mile on grid electricity

-As the table shows, not only are batteries very efficient ways to store electricity, but

electric motors are very efficient ways to convert electricity to traction. Unlike internalcombustion engines, which at best might convert 35% of the energy in gasoline intohorsepower, an electric motor will convert 90% of the electrical input into horsepower.Since a kilowatt of output is equivalent to 1.341 horsepower of output, it is possible tocalculate how a given amount of grid electricity expressed in kilowatt-hours will beavailable in the form of horsepower-hours to power a vehicle.In the example above, the average car requires 20 horsepower to drive at a speed of 50miles-per-hour on a level surface. On this basis, the average car requires 370 watt-hoursof power to go one mile. At $10 per kilowatt-hour, it only costs you 3.7 cents to travelone mile. Compare this to an economy sedan that gets 30 miles per gallon. At $3.00 pergallon gasoline, it will cost nearly three times as much, $.10 per mile, to drive this car

using gasoline. And at night when electric cars are being charged, electricity rates areoften much lower than $.10 per kilowatt-hour. It is possible to drive an electric car for aslittle as $.02 per mile! This arbitrage between the cost per mile of gasoline power vs. thecost per mile of electrical power is an awesome opportunity, but only one that can beexploited by battery-powered cars, which can convert 90% of grid electricity into powergoing into the motor, compared to the electrolyser / fuel cell combination, which only candeliver 42% of grid electricity into power going into the motor.


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ELECTRIC CAR RANGE WITH A 1,000 POUND BATTERYPACK

At only 100 watt-hours per KG, 1,000 lbs. of batteries gets 123 miles

-Advances in battery technology are inevitable, as hybrid cars enter the mainstream ofautomotive technology. Toyota is planning on manufacturing, per year, over one millionhybrid cars by 2010. Other manufacturers are following suit. At the least, vehiclebatteries are going to get cheaper, more temperature tolerant, longer lasting, and cleanerto recycle and reprocess. At best, vehicle batteries, such as the lithium ion batteries, willenter mass production, allowing 200+ watt-hour per kilogram batteries to power electriccars. Weight as a core problem for electric cars will begin to disappear entirely if lithiumion batteries ever enter mass production.In the meantime, its safe to say nickel metal hydride batteries are here to stay, and theyare becoming increasingly available, durable, and cheap. The EV-1 had a battery pack

that weighed 1,600 pounds. This is quite a payload. Using nickel metal hydride batteries,the battery payload can be reduced to 1,000 pounds, concentrated along the center spineof the car. Assuming 100 watt-hours per kilogram, which is easily attainable usingtodays nickel metal hydride batteries, such a car fully charged would have 45 kilowatt-hours available to power the motor. Assuming 2.7 miles per kilowatt-hour, a car with a1,000 pound battery payload at 100 watt-hours per kilogram of batteries will have a rangeof 123 miles. Is this great? No. Is this enough to get to work and back? At two cents permile, you bet it is, and all you do is plug the car in at night. No more gas stations.

SERIES HYBRID CARADVANCED PROTOTYPE (side view)

photovoltaic skin


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optimally aerodynamic(elec=R, batt=G, diesel=O)

The biggest problem with electric cars, unlike gasoline powered cars or hydrogen-powered cars, for that matter is the time it takes to recharge the batteries. This is why

gasoline-electric hybrids are getting an early foothold in the battle for the car of thefuture. When a gas/electric hybrids batteries run out of juice, the car can still limp along,powered solely by the gasoline engine. This is also why hybrid mileage is somewhatmisleading. The more battery power is used, the better the mileage. For stop and go, lowspeed driving, the gasoline engine can divert energy to recharging the batteries faster thantheyre being depleted. On extended runs at high speeds, or up hills, however, thegasoline engine must use all its energy to power the car, assisted by the battery-poweredelectric motor. This drains the batteries and turns the hybrid, basically, into anunderpowered gas-powered car that has to carry a lot of dead weight. In these scenarios,mileage plummets. In a nutshell, the hybrid car has a lot of the same weaknesses as abattery-powered car, except it wont leave you stranded when the batteries run low, just

hobbled.The idea that a 100% battery-powered car isnt a viable vehicle solution because of itslimited range, however, is to ignore the duty cycle that the vast majority of vehicle tripsentails a short range errand or commute. Most American families have two cars. Whywouldnt it make sense particularly at two-cents per mile for one of those two cars bea 100% electric car?If an electric car is defined as a vehicle that derives 100% of its horsepower from anelectric motor, there are many ways to supplement the cars range. For example, a hybridcar typically depends on two engines to power the vehicle, an electric motor combinedwith a gasoline engine usually between 40-60 horsepower. But what if a gasoline engine,perhaps a highly efficient biodiesel engine, were used to power an onboard generator and

was completely disconnected from the drive train?

RANGE ADDED WITH AN ONBOARD DIESEL GENERATOR

An on-board 20 horsepower generator doubles the range of batteries

-This is the case for the serial hybrid. An ultra-efficient, steady-RPM clean diesel motor turning an electric generator running whenever the car was operating, could rechargeon-board batteries at a rate at or near the amount theyre depleted. If only a tenhorsepower generator were used, assuming a generator efficiency of 90%, then for every


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hour on the road, 18 miles of range would be added. Using the example above, a car witha 1,000 lb. battery pack has a range of 123 miles per charge; at 60 mph the car hasextended its range another 47 miles (or so), which means that now the car can go 170miles on a charge with a few gallons of biodiesel. Remember, this engine is less thanone fourth the size of the already tiny gas engines in hybrid cars.

If in your serial-hybrid car where a diesel powered generator powers a battery-pack thatpowers an electric motor you use a 20 horsepower diesel powered on-board generator,the range becomes very practical. Running a 20 horsepower generator, still a very smallengine, will allow you to add 36 miles of range for every hour your battery-powered caris driven. Now you can drive your car 250 miles on a charge. Such a trip would requirefour gallons of gas and 45 kilowatt-hours of grid electricity. At $3.00 per gallon & .10per kilowatt-hour, your combined-fuel cost per mile would be about five cents.The advanced electric car can be built using advanced technology and materials alightweight ultra-strong frame, aerodynamic exoskeleton, in-wheel motors withindependent 360 degree wheel rotation in all four wheels, driver control by wire,autopilot, lithium ion batteries, photovoltaic sides and windows, the works.

SERIES HYBRID CARBASIC CONVERSION (side view)

Generic photovoltaic flat-panelsplaced on cover to truck bed.

(elec=R, batt=G, diesel=O)

But a practical electric car can also be built by converting a small gasoline pickup truck,removing the gas engine and replacing it with an electric one. The transmission could bereplaced by a single-speed reduction box that would last forever. In the bed of the pickupa 10-20 horsepower diesel generator could be bolted on, to power a battery-pack whichwould fill much of the rest of the bed of the pickup. Additional batteries could beinstalled on racks riding on the cars undercarriage starting where the gas tank isremoved. The top of the bed of the pickup would have a flat hood covered completelywith photovoltaic panels, enough to add scores of miles per day of range to the batterypack. You would have a commuting truck you could refuel with either a plug into the

wall, a pump at the gas station, or parking in the sun.Entrepreneurs, investors, electrical engineers, auto-mechanics: All you need are usedgasoline cars, electric motors and batteries. Who will make the electric car that refuels inthe sun?


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Battery (electricity)

From Wikipedia, the free encyclopedia

Jump to: navigation, search

For other uses, see Battery (disambiguation).

Various cells and batteries (top-left to bottom-right): two AA, one D, one handheld ham radio battery,

two 9-volt (PP3), two AAA, one C, one camcorder battery, one cordless phone battery.

An electrical battery is one or more electrochemical cells that convert stored chemical energy

into electrical energy.

[1]

Since the invention of the first battery (or "voltaic pile") in 1800 byAlessandro Volta, batteries have become a common power source for many household andindustrial applications. According to a 2005 estimate, the worldwide battery industry generatesUS$48billion in sales each year,[2] with 6% annual growth.[3]

There are two types of batteries:primary batteries (disposable batteries), which are designed tobe used once and discarded, and secondary batteries (rechargeable batteries), which are designedto be recharged and used multiple times. Miniature cells are used to power devices such ashearing aids and wristwatches; larger batteries provide standby power for telephone exchanges orcomputer data centers.


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Contents

[hide]

y 1 History

y 2 Principle of operationy 3 Categories and types of batteries

o 3.1 Primary batteries

o 3.2 Secondary batteries

o 3.3 Battery cell types

3.3.1 Wet cell

3.3.2 Dry cell

3.3.3 Molten salt

3.3.4 Reserve

o 3.4 Battery cell performance

y 4 Battery capacity and discharging

o 4.1 Fastest charging, largest, and lightest batteries

y 5 Battery lifetime

o 5.1 Life of primary batteries

5.1.1 Battery sizes

o 5.2 Lifespan of rechargeable batteries

o 5.3 Extending battery life

o 5.4 Prolonging life in multiple cells through cell balancing

y 6 Hazards

o 6.1 Explosion

o 6.2 Leakage

o 6.3 Environmental concerns

o 6.4 Ingestion

y 7 Battery chemistryo 7.1 Primary battery chemistries

o 7.2 Rechargeable battery chemistries

y 8 Homemade cells

y 9 See also

y 10 References

y 11 Further reading

y 12 External links

[edit] History

Main article: History of the battery


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The symbol for a battery in a circuit diagram. It originated as a schematic drawing of the earliest type of

battery, a voltaic pile.

Strictly, a battery is a collection of multiple electrochemical cells, but in popular usage batteryoften refers to a single cell.[1] The first electrochemical cell was developed by the Italian

physicist Alessandro Volta in 1792, and in 1800 he invented the first batteryfor him, a "pile"of cells.[4]

The usage of "battery" to describe electrical devices dates to Benjamin Franklin, who in 1748described multiple Leyden jars (early electrical capacitors) by analogy to abattery of cannons.[5]Thus Franklin's usage to describe multiple Leyden jars predated Volta's use of multiple galvaniccells.

[6]It is speculated, but not established, that several ancient artifacts consisting of copper

sheets and iron bars, and known as Baghdad batteries may have been galvanic cells.[7]

Volta's work was stimulated by the Italian anatomist and physiologist Luigi Galvani, who in1780 noticed that dissected frog's legs would twitch when struck by a spark from a Leyden jar,

an external source of electricity.[8]

In 1786 he noticed that twitching would occur duringlightning storms.[9] After many years Galvani learned how to produce twitching without usingany external source of electricity. In 1791 he published a report on "animal electricity."[10] Hecreated an electric circuit consisting of the frog's leg (FL) and two different metals A and B, eachmetal touching the frog's leg and each other, thus producing the circuit A-FL-B-A-FL-B...etc. Inmodern terms, the frog's leg served as both the electrolyte and the sensor, and the metals servedas electrodes. He noticed that even though the frog was dead, its legs would twitch when hetouched them with the metals.

Within a year, Volta realized the frog's moist tissues could be replaced by cardboard soaked insalt water, and the frog's muscular response could be replaced by another form of electrical

detection. He already had studied the electrostatic phenomenon ofcapacitance, which requiredmeasurements of electric charge and of electrical potential ("tension"). Building on thisexperience, Volta was able to detect electric current through his system, also called a Galvaniccell. The terminal voltage of a cell that is not discharging is called its electromotive force (emf),and has the same unit as electrical potential, named (voltage) and measured in volts, in honor ofVolta. In 1800, Volta invented the battery by placing many voltaic cells in series, literally pilingthem one above the other. This voltaic pile gave a greatly enhanced net emf for the


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combination,[11] with a voltage of about 50 volts for a 32-cell pile.[12] In many parts of Europebatteries continue to be called piles.[13][14]

Volta did not appreciate that the voltage was due to chemical reactions. He thought that his cellswere an inexhaustible source of energy,[15] and that the associated chemical effects at the

electrodes (e.g. corrosion) were a mere nuisance, rather than an unavoidable consequence of theiroperation, as Michael Faraday showed in 1834.[16] According to Faraday, cations (positivelycharged ions) are attracted to the cathode,[17] and anions (negatively charged ions) are attracted tothe anode.

[18]

Although early batteries were of great value for experimental purposes, in practice their voltagesfluctuated and they could not provide a large current for a sustained period. Later, starting withthe Daniell cell in 1836, batteries provided more reliable currents and were adopted by industryfor use in stationary devices, particularly in telegraph networks where they were the onlypractical source of electricity, since electrical distribution networks did not exist at the time.[19]These wet cells used liquid electrolytes, which were prone to leakage and spillage if not handled

correctly. Many used glass jars to hold their components, which made them fragile. Thesecharacteristics made wet cells unsuitable for portable appliances. Near the end of the nineteenthcentury, the invention ofdry cell batteries, which replaced the liquid electrolyte with a paste,made portable electrical devices practical.[20]

Since then, batteries have gained popularity as they became portable and useful for a variety ofpurposes.[21]

[edit] Principle of operation

Main article: Electrochemical cell

A voltaic cell for demonstration purposes. In this example the two half-cells are linked by a salt bridge

separator that permits the transfer of ions, but not water molecules.

A battery is a device that converts chemical energy directly to electrical energy.[22] It consists ofa number of voltaic cells; each voltaic cell consists of two half cells connected in series by aconductive electrolyte containing anions and cations. One half-cell includes electrolyte and the


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electrode to which anions (negatively charged ions) migrate, i.e., the anode or negative electrode;the other half-cell includes electrolyte and the electrode to which cations (positively chargedions) migrate, i.e., the cathode or positive electrode. In the redox reaction that powers the battery,reduction (addition of electrons) occurs to cations at the cathode, while oxidation (removal ofelectrons) occurs to anions at the anode.[23] The electrodes do not touch each other but are

electrically connected by the electrolyte. Some cells use two half-cells with different electrolytes.A separator between half cells allows ions to flow, but prevents mixing of the electrolytes.

Each half cell has an electromotive force (or emf), determined by its ability to drive electriccurrent from the interior to the exterior of the cell. The net emf of the cell is the differencebetween the emfs of its half-cells, as first recognized by Volta.[12] Therefore, if the electrodes

have emfs and , then the net emf is ; in other words, the net emf is the differencebetween the reduction potentials of the half-reactions.[24]

The electrical driving force or across the terminals of a cell is known as the terminalvoltage (difference) and is measured in volts.[25] The terminal voltage of a cell that is neither

charging nor discharging is called the open-circuit voltage and equals the emf of the cell.Because of internal resistance,[26] the terminal voltage of a cell that is discharging is smaller inmagnitude than the open-circuit voltage and the terminal voltage of a cell that is chargingexceeds the open-circuit voltage.[27] An ideal cell has negligible internal resistance, so it wouldmaintain a constant terminal voltage of until exhausted, then dropping to zero. If such a cellmaintained 1.5 volts and stored a charge of one coulomb then on complete discharge it wouldperform 1.5joule of work.[25] In actual cells, the internal resistance increases under discharge,[26]and the open circuit voltage also decreases under discharge. If the voltage and resistance areplotted against time, the resulting graphs typically are a curve; the shape of the curve variesaccording to the chemistry and internal arrangement employed.[28]

As stated above, the voltage developed across a cell's terminals depends on the energy release ofthe chemical reactions of its electrodes and electrolyte. Alkaline and carbon-zinc cells havedifferent chemistries but approximately the same emf of 1.5 volts; likewiseNiCd andNiMHcells have different chemistries, but approximately the same emf of 1.2 volts.[29] On the otherhand the high electrochemical potential changes in the reactions oflithium compounds givelithium cells emfs of 3 volts or more.[30]

[edit] Categories and types of batteries

Main article: List of battery types


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From top to bottom: SR41/AG3, SR44/AG13 (button cells), a 9-volt PP3 battery, anAAA cell, anAA cell, a

C cell, a D Cell, and a large 3R12. The ruler's unit is in centimeters.

Batteries are classified into two broad categories, each type with advantages anddisadvantages.[31]

y Primarybatteries irreversibly (within limits of practicality) transform chemical energy to

electrical energy. When the initial supply of reactants is exhausted, energy cannot be readily

restored to the battery by electrical means.[32]

y Secondarybatteries can be recharged; that is, they can have their chemical reactions reversed

by supplying electrical energy to the cell, restoring their original composition.[33]


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Historically, some types of primary batteries used, for example, fortelegraph circuits, wererestored to operation by replacing the components of the battery consumed by the chemicalreaction.

[34]Secondary batteries are not indefinitely rechargeable due to dissipation of the active

materials, loss of electrolyte and internal corrosion.

[edit] Primary batteries

Main article: Primary cell

Primary batteries can produce current immediately on assembly. Disposable batteries areintended to be used once and discarded. These are most commonly used in portable devices thathave low current drain, are only used intermittently, or are used well away from an alternativepower source, such as in alarm and communication circuits where other electric power is onlyintermittently available. Disposable primary cells cannot be reliably recharged, since thechemical reactions are not easily reversible and active materials may not return to their originalforms. Battery manufacturers recommend against attempting to recharge primary cells.[35]

Common types of disposable batteries include zinc-carbon batteries and alkaline batteries.Generally, these have higherenergy densities than rechargeable batteries,[36] but disposablebatteries do not fare well under high-drain applications with loads under 75 ohms (75 ).[31]

[edit] Secondary batteries

Main article: Rechargeable battery

Secondary batteries must be charged before use; they are usually assembled with active materialsin the discharged state. Rechargeable batteries orsecondary cells can be recharged by applying

electric current, which reverses the chemical reactions that occur during its use. Devices tosupply the appropriate current are called chargers or rechargers.

The oldest form of rechargeable battery is the lead-acid battery.[37] This battery is notable in thatit contains a liquid in an unsealed container, requiring that the battery be kept upright and thearea be well ventilated to ensure safe dispersal of the hydrogen gas produced by these batteriesduring overcharging. The lead-acid battery is also very heavy for the amount of electrical energyit can supply. Despite this, its low manufacturing cost and its high surge current levels make itsuse common where a large capacity (over approximately 10Ah) is required or where the weightand ease of handling are not concerns.

A common form of the lead-acid battery is the modern car battery, which can generally deliver apeak current of 450 amperes.[38] An improved type of liquid electrolyte battery is the sealed valveregulated lead acid (VRLA) battery, popular in the automotive industry as a replacement for thelead-acid wet cell. The VRLA battery uses an immobilized sulfuric acid electrolyte, reducing thechance of leakage and extending shelf life.[39] VRLA batteries have the electrolyte immobilized,usually by one of two means:

y Gel batteries (or "gel cell") contain a semi-solid electrolyte to prevent spillage.


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y AbsorbedGlass Mat(AGM) batteries absorb the electrolyte in a special fiberglass matting.

Other portable rechargeable batteries include several "dry cell" types, which are sealed units andare therefore useful in appliances such as mobile phones and laptop computers. Cells of this type(in order of increasingpower density and cost) include nickel-cadmium (NiCd), nickel-zinc

(NiZn), nickel metal hydride (NiMH) and lithium-ion (Li-ion) cells.

[40]

By far, Li-ion has thehighest share of the dry cell rechargeable market.[3] Meanwhile, NiMH has replaced NiCd inmost applications due to its higher capacity, but NiCd remains in use inpower tools, two-wayradios, and medical equipment.[3] NiZn is a new technology that is not yet well establishedcommercially.

Recent developments include batteries with embedded functionality such as USBCELL, with abuilt-in charger and USB connector within the AA format, enabling the battery to be charged byplugging into a USB port without a charger,[41] and low self-discharge (LSD) mix chemistriessuch as Hybrio,[42] ReCyko,[43] and Eneloop,[44] where cells are precharged prior to shipping.

[edit] Battery cell types

There are many general types of electrochemical cells, according to chemical processes appliedand design chosen. The variation includes galvanic cells, electrolytic cells, fuel cells, flow cellsand voltaic piles.[45]

[edit] Wet cell

A wet cellbattery has a liquid electrolyte. Other names areflooded cellsince the liquid covers allinternal parts, orvented cellsince gases produced during operation can escape to the air. Wetcells were a precursor to dry cells and are commonly used as a learning tool forelectrochemistry.

It is often built with common laboratory supplies, likebeakers, for demonstrations of howelectrochemical cells work. A particular type of wet cell known as a concentration cell isimportant in understanding corrosion. Wet cells may beprimary cells (non-rechargeable) orsecondary cells (rechargeable). Originally all practical primary batteries such as the Daniell cellwere built as open-topped glass jar wet cells. Other primary wet cells are the Leclanche cell,Grove cell, Bunsen cell, Chromic acid cell, Clark cell and Weston cell. The Leclanche cellchemistry was adapted to the first dry cells. Wet cells are still used in automobile batteries and inindustry for standby power forswitchgear, telecommunication or large uninterruptible powersupplies, but in many places batteries with gel cells have been used instead. These applicationscommonly use lead-acid ornickel-cadmium cells.

[edit] Dry cell

"Dry cell"redirects here. For the heavy metal band, see Dry Cell (band).


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Line art drawing of a dry cell:

1. brass cap, 2. plastic seal, 3. expansion space, 4. porous cardboard, 5. zinc can, 6. carbon rod, 7.

chemical mixture.

A dry cellhas the electrolyte immobilized as a paste, with only enough moisture in the paste toallow current to flow. As opposed to a wet cell, the battery can be operated in any randomposition, and will not spill its electrolyte if inverted.

While a dry cell's electrolyte is not truly completely free of moisture and must contain somemoisture to function, it has the advantage of containing no sloshing liquid that might leak or dripout when inverted or handled roughly, making it highly suitable for small portable electricdevices. By comparison, the first wet cells were typically fragile glass containers with lead rodshanging from the open top, and needed careful handling to avoid spillage. An inverted wet cellwould leak, while a dry cell would not. Lead-acid batteries would not achieve the safety andportability of the dry cell until the development of the gel battery.

A common dry cell battery is the zinc-carbon battery, using a cell sometimes called the dryLeclanch cell, with a nominal voltage of 1.5 volts, the same nominal voltage as the alkalinebattery (since both use the same zinc-manganese dioxide combination).

The makeup of a standard dry cell is a zinc anode (negative pole), usually in the form of acylindrical pot, with a carbon cathode (positive pole) in the form of a central rod. The electrolyteis ammonium chloride in the form of a paste next to the zinc anode. The remaining spacebetween the electrolyte and carbon cathode is taken up by a second paste consisting ofammonium chloride and manganese dioxide, the latter acting as a depolariser. In some moremodern types of so called 'high power' batteries, the ammonium chloride has been replaced byzinc chloride.

[edit] Molten salt


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A molten salt battery is a primary or secondary battery that uses a molten salt as its electrolyte.Theirenergy density andpower density makes them potentially useful forelectric vehicles, butthey must be carefully insulated to retain heat.

[edit] Reserve

A reserve battery can be stored for a long period of time and is activated when its internal parts(usually electrolyte) are assembled. For example, a battery for an electronic fuze might beactivated by the impact of firing a gun, breaking a capsule of electrolyte to activate the batteryand power the fuze's circuits. Reserve batteries are usually designed for a short service life(seconds or minutes) after long storage (years). A water-activated battery for oceanographicinstruments or military applications becomes activated on immersion in water.

[edit] Battery cell performance

A battery's characteristics may vary over load cycle, charge cycle and over lifetime due to many

factors including internal chemistry, current drain and temperature.

[edit] Battery capacity and discharging

A device to check battery voltage.

The more electrolyte and electrode material there is in the cell, the greater the capacity of thecell. Thus a small cell has less capacity than a larger cell, given the same chemistry (e.g. alkalinecells), though they develop the same open-circuit voltage.[46]

Because of the chemical reactions within the cells, the capacity of a battery depends on thedischarge conditions such as the magnitude of the current (which may vary with time), the

allowable terminal voltage of the battery, temperature and other factors.[46]

The availablecapacity of a battery depends upon the rate at which it is discharged.[47] If a battery is dischargedat a relatively high rate, the available capacity will be lower than expected.

The battery capacity that battery manufacturers print on a battery is usually the product of 20hours multiplied by the maximum constant current that a new battery can supply for 20 hours at68 F (20 C), down to a predetermined terminal voltage per cell. A battery rated at 100 Ah will


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deliver 5 A over a 20 hour period at room temperature. However, if it is instead discharged at 50A, it will have a lower apparent capacity.[48]

The relationship between current, discharge time, and capacity for a lead acid battery isapproximated (over a certain range of current values) by Peukert's law:

where

QPis the capacity when discharged at a rate of1 amp.

Iis the current drawn from battery (A).

tis the amount of time (in hours) that a battery can sustain.

kis a constant around 1.3.

For low values ofI internal self-discharge must be included.

In practical batteries, internal energy losses, and limited rate of diffusion of ions through theelectrolyte, cause the efficiency of a battery to vary at different discharge rates. Whendischarging at low rate, the battery's energy is delivered more efficiently than at higher dischargerates,[48] but if the rate is too low, it will self-discharge during the long time of operation, againlowering its efficiency.

Installing batteries with different Ah ratings will not affect the operation of a device rated for aspecific voltage unless the load limits of the battery are exceeded. High-drain loads like digitalcameras can result in lower actual energy, most notably for alkaline batteries.[31] For example, abattery rated at 2000 mAh would not sustain a current of 1 A for the full two hours, if it hadbeen rated at a 10-hour or 20-hour discharge.

[edit] Fastest charging, largest, and lightest batteries

Lithium iron phosphate (LiFePO4) batteries are the fastest charging and discharging, next tosupercapacitors.[49] The world's largest battery is in Fairbanks, Alaska, composed ofNi-Cd

cells.[50]

Sodium-sulfur batteries are being used to store wind power.[51]

Lithium-sulfur batterieshave been used on the longest and highest solar powered flight.[52] The speed of recharging forlithium-ion batteries may be increased by manipulation.[53]

[edit] Battery lifetime

[edit] Life of primary batteries


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Even if never taken out of the original package, disposable (or "primary") batteries can lose 8 to20 percent of their original charge every year at a temperature of about 2030C.[54] This isknown as the "self discharge" rate and is due to non-current-producing "side" chemical reactions,which occur within the cell even if no load is applied to it. The rate of the side reactions isreduced if the batteries are stored at low temperature, although some batteries can be damaged by

freezing. High or low temperatures may reduce battery performance. This will affect the initialvoltage of the battery. For an AA alkaline battery this initial voltage is approximately normallydistributed around 1.6 volts.

Discharging performance of all batteries drops at low temperature.[55]

[edit] Battery sizes

Main article: List of battery sizes

[edit] Lifespan of rechargeable batteries

Rechargeable batteries.

Rechargeable batteries self-discharge more rapidly than disposable alkaline batteries, especiallynickel-based batteries; a freshly charged NiCd loses 10% of its charge in the first 24 hours, andthereafter discharges at a rate of about 10% a month.[56] However, modern lithium designs havereduced the self-discharge rate to a relatively low level (but still poorer than for primarybatteries).[56] Most nickel-based batteries are partially discharged when purchased, and must becharged before first use.[57]

Although rechargeable batteries have their energy content restored by charging, somedeterioration occurs on each charge/discharge cycle. Low-capacity nickel metal hydride (NiMH)batteries (1700-2000 mAh) can be charged for about 1000 cycles, whereas high capacity NiMHbatteries (above 2500 mAh) can be charged for about 500 cycles.[58] Nickel cadmium (NiCd)batteries tend to be rated for 1,000 cycles before their internal resistance permanently increasesbeyond usable values. Normally a fast charge, rather than a slow overnight charge, will shortenbattery lifespan.[58] However, if the overnight charger is not "smart" and cannot detect when thebattery is fully charged, then overcharging is likely, which also damages the battery.

[59]


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Degradation usually occurs because electrolyte migrates away from the electrodes or becauseactive material falls off the electrodes. NiCd batteries suffer the drawback that they should befully discharged before recharge. Without full discharge, crystals may build up on the electrodes,thus decreasing the active surface area and increasing internal resistance. This decreases batterycapacity and causes the "memory effect". These electrode crystals can also penetrate the

electrolyte separator, thereby causing shorts. NiMH, although similar in chemistry, does notsuffer from memory effect to quite this extent.[60] When a battery reaches the end of its lifetime,it will not suddenly lose all of its capacity; rather, its capacity will gradually decrease.[61]

Automotive lead-acid rechargeable batteries have a much harder life.[62] Because of vibration,shock, heat, cold, and sulfation of their lead plates, few automotive batteries last beyond sixyears of regular use.[63] Automotive starting batteries have many thin plates to provide as muchcurrent as possible in a reasonably small package. In general, the thicker the plates, the longerthe life of the battery.[62] Typically they are only drained a small amount before recharge. Careshould be taken to avoid deep discharging a starting battery, since each charge and dischargecycle causes active material to be shed from the plates.

"Deep-cycle" lead-acid batteries such as those used in electric golf carts have much thicker platesto aid their longevity.[64] The main benefit of the lead-acid battery is its low cost; the maindrawbacks are its large size and weight for a given capacity and voltage.[62] Lead-acid batteriesshould never be discharged to below 20% of their full capacity,[65] because internal resistancewill cause heat and damage when they are recharged. Deep-cycle lead-acid systems often use alow-charge warning light or a low-charge power cut-off switch to prevent the type of damagethat will shorten the battery's life.[66]

[edit] Extending battery life

Battery life can be extended by storing the batteries at a low temperature, as in a refrigeratororfreezer, which slows the chemical reactions in the battery. Such storage can extend the life ofalkaline batteries by about 5%, while the charge of rechargeable batteries can be extended from afew days up to several months.[67] To reach their maximum voltage, batteries must be returned toroom temperature; discharging an alkaline battery at 250 mAh at 0C is only half as efficient asit is at 20C.[36] As a result, alkaline battery manufacturers like Duracell do not recommendrefrigerating or freezing batteries.[35]

[edit] Prolonging life in multiple cells through cell balancing

Analog front ends that balance cells and eliminate mismatches of cells in series or parallel

combination significantly improve battery efficiency and increase the overall pack capacity. Asthe number of cells and load currents increase, the potential for mismatch also increases. Thereare two kinds of mismatch in the pack: state-of-charge (SOC) and capacity/energy (C/E)mismatch. Though the SOC mismatch is more common, each problem limits the pack capacity(mAh) to the capacity of the weakest cell.

Cell balancing principle


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Battery pack cells are balanced when all the cells in the battery pack meet two conditions:

1. If all cells have the same capacity, then they are balanced when they have the same State of

Charge (SOC.) In this case, the Open Circuit Voltage (OCV) is a good measure of the SOC. If, in an

out of balance pack, all cells can be differentially charged to full capacity (balanced), then they

will subsequently cycle normally without any additional adjustments. This is mostly a one shot

fix.

2. If the cells have different capacities, they are also considered balanced when the SOC is the

same. But, since SOC is a relative measure, the absolute amount of capacity for each cell is

different. To keep the cells with different capacities at the same SOC, cell balancing must

provide differential amounts of current to cells in the series string during both charge and

discharge on every cycle.

Cell balancing electronics

Cell balancing is defined as the application of differential currents to individual cells (orcombinations of cells) in a series string. Normally, of course, cells in a series string receiveidentical currents. A battery pack requires additional components and circuitry to achieve cellbalancing. However, the use of a fully integrated analog front end for cell balancing reduces therequired external components to just balancing resistors.

It is important to recognize that the cell mismatch results more from limitations in processcontrol and inspection than from variations inherent in the Lithium Ion chemistry. The use of afully integrated analog front end for cell balancing can improve the performance of seriesconnected Li-ion Cells by addressing both SOC and C/E issues.[68] SOC mismatch can beremedied by balancing the cell during an initial conditioning period and subsequently onlyduring the charge phase. C/E mismatch remedies are more difficult to implement and harder tomeasure and require balancing during both charge and discharge periods.

This type of solution eliminates the quantity of external components, as for discrete capacitors,diodes and most other resistors to achieve balance.

[edit] Hazards

[edit] Explosion

A battery explosion is caused by the misuse or malfunction of a battery, such as attempting torecharge a primary (non-rechargeable) battery,[69] orshort circuiting a battery.[70] With car

batteries, explosions are most likely to occur when a short circuit generates very large currents.In addition, car batteries liberate hydrogen when they are overcharged (because ofelectrolysis ofthe water in the electrolyte). Normally the amount of overcharging is very small, as is the amountof explosive gas developed, and the gas dissipates quickly. However, when "jumping" a carbattery, the high current can cause the rapid release of large volumes of hydrogen, which can beignited by a nearby spark (for example, when removing the jumper cables).


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When a battery is recharged at an excessive rate, an explosive gas mixture of hydrogen andoxygen may be produced faster than it can escape from within the walls of the battery, leading topressure build-up and the possibility of the battery case bursting. In extreme cases, the batteryacid may spray violently from the casing of the battery and cause injury. Overchargingthat is,attempting to charge a battery beyond its electrical capacitycan also lead to a battery

explosion, leakage, or irreversible damage to the battery. It may also cause damage to the chargeror device in which the overcharged battery is later used. Additionally, disposing of a battery infire may cause an explosion as steam builds up within the sealed case of the battery.[70]

[edit] Leakage

Leaked alkaline battery.

Many battery chemicals are corrosive, poisonous, or both. If leakage occurs, eitherspontaneously or through accident, the chemicals released may be dangerous.

For example, disposable batteries often use a zinc "can" as both a reactant and as the container to

hold the other reagents. If this kind of battery is run all the way down, or if it is recharged afterrunning down too far, the reagents can emerge through the cardboard and plastic that form theremainder of the container. The active chemical leakage can then damage the equipment that thebatteries were inserted into. For this reason, many electronic device manufacturers recommendremoving the batteries from devices that will not be used for extended periods of time.

Environmental concerns

The widespread use of batteries has created many environmental concerns, such as toxic metalpollution.[71] Battery manufacture consumes resources and often involves hazardous chemicals.Used batteries also contribute to electronic waste. Some areas now have battery recycling

services available to recover some of the materials from used batteries.[72] Batteries may beharmful or fatal ifswallowed.[73] Recycling or proper disposal prevents dangerous elements(such as lead, mercury, and cadmium) found in some types of batteries from entering theenvironment. In the United States, Americans purchase nearly three billion batteries annually,and about 179,000 tons of those end up in landfills across the country.[74]

In the United States, the Mercury-Containing and Rechargeable Battery Management Act of1996 banned the sale of mercury-containing batteries, enacted uniform labeling requirements for


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rechargeable batteries, and required that rechargeable batteries be easily removable.[75]California, and New York City prohibit the disposal of rechargeable batteries in solid waste, andalong with Maine require recycling of cell phones.

[76]The rechargeable battery industry has

nationwide recycling programs in the United States and Canada, with dropoff points at localretailers.[76]

The Battery Directive of the European Union has similar requirements, in addition to requiringincreased recycling of batteries, and promoting research on improved battery recyclingmethods.

[77]

Ingestion

Small button/disk batteries can be swallowed by young children. While in the digestive tract thebattery's electrical discharge can burn the tissues and can be serious enough to lead to death.[78]Disk batteries do not usually cause problems unless they become lodged in the gastrointestinal(GI) tract. The most common place disk batteries become lodged, resulting in clinical sequelae,

is the esophagus. Batteries that successfully traverse the esophagus are unlikely to lodge at anyother location. The likelihood that a disk battery will lodge in the esophagus is a function of thepatient's age and the size of the battery. Disk batteries of 16 mm have become lodged in theesophagi of 2 children younger than 1 year. Older children do not have problems with batteriessmaller than 2123 mm. For comparison, a dime is 18 mm, a nickel is 21 mm, and a quarter is24 mm. Liquefaction necrosis may occur because sodium hydroxide is generated by the currentproduced by the battery (usually at the anode). Perforation has occurred as rapidly as 6 hoursafter ingestion

how does a battery produce electricity

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