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10/13/2016 Battery AccessScience from McGrawHill Education

http://www.accessscience.com/content/battery/075200 1/24

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BatteryArticle by:

Anglin, Donald L. Consultant, Automotive and Technical Writing, Charlottesville, Virginia.

Sadoway, Donald R. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts.

Publication year: 2014

DOI: http://dx.doi.org/10.1036/10978542.075200 (http://dx.doi.org/10.1036/10978542.075200)

Content

TypesComponentsSizeSelection and applicationsRatingsLifePrimary BatteriesZinccarbon cellsMagnesium cellsAlkalinemanganese dioxide cellsMercuric oxide cellsSilver oxide cellsZincair cellsLithium cellsSolidelectrolyte cellsReserve batteriesZincsilver oxide reserve batteriesMagnesium wateractivated batteriesLithiumanode reserve batteriesThermal batteriesSecondary BatteriesLeadacid batteriesNickelcadmium batteriesNickelmetal hydride batteriesSilverzinc batteriesSodiumsulfur batteriesZincair batteriesLithiumion batteriesLithiumsolid polymer electrolyte (SPE) batteriesOutlookBibliographyAdditional Readings

An electrochemical device that stores chemical energy which can be converted into electrical energy, thereby providing adirectcurrent voltage source. Although the term “battery” is properly applied to a group of two or more electrochemical cellsconnected together electrically, both singlecell and multicell devices are called battery. See also: Electrochemistry(/content/electrochemistry/220300); Electromotive force (cells) (/content/electromotiveforcecells/223300)

Types

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The two general types are the primary battery and the secondary battery. The primary battery delivers current as the resultof a chemical reaction that is not efficiently reversible. Practically, this makes the primary battery nonrechargeable. Onlyone intermittent or continuous discharge can be obtained before the chemicals placed in it during manufacture areconsumed. Then the discharged primary battery must be replaced. The secondary or storage battery is rechargeablebecause it delivers current as the result of a chemical reaction that is easily reversible. When a charging current flowsthrough its terminals in the direction opposite to the current flow during discharge, the active materials in the secondarybattery return to approximately their original charged condition.

ComponentsThe cell is the basic electrochemical unit. It has three essential parts: (1) a negative electrode (the anode) and (2) apositive electrode (the cathode) that are in contact with (3) an electrolyte solution. The electrodes are metal rods, sheets, orplates that are used to receive electrical energy (in secondary cells), store electrical energy chemically, and deliverelectrical energy as the result of the reactions that occur at the electrodesolution surfaces. Solid polymer or plastic activematerials have been developed that can serve as the cathode in rechargeable batteries. The electrolyte is a chemicalcompound (salt, acid, or base) that when dissolved in a solvent forms a solution that becomes an ionic conductor ofelectricity, but essentially insulating toward electrons—properties that are prerequisites for any electrolyte. In the cell orbattery, this electrolyte solution is the conducting medium in which the flow of electric current between electrodes takesplace by the migration of ions. When water is the solvent, an aqueous solution is formed. Some cells have a nonaqueouselectrolyte, for example, when alcohol is used as the solvent. Other cells have a solid electrolyte that when used with solidelectrodes can form a leakfree solidstate cell or battery.

During charging of a secondary cell, the negative electrode becomes the cathode and the positive electrode becomes theanode. However, electrode designation as positive or negative is unaffected by the operating mode of the cell or battery.Two or more cells internally connected together electrically, in series or parallel, form a battery of a given voltage. Typicalare the rectangular 9V primary battery, which has six flat 1.5V zinccarbon or alkaline “dry” cells connected in series, andthe 12V automotive or secondary battery, which has six 2.1V leadacid “wet” cells connected in series.

SizeBoth primary and secondary cells are manufactured in many sizes, shapes, and terminal arrangements, from the miniaturecoin or buttonshaped battery (which has a diameter greater than its height) and the small cylindrical penlight battery to thelarge submarine battery, where a single rectangular cell has weighed 1 ton (0.9 metric ton). For optimum performance, thebattery must be constructed for its particular application consistent with cost, weight, space, and operational requirements.Automotive and aircraft batteries are secondary batteries that have relatively thin positive and negative plates with thin,porous, envelope separators to conserve space and weight and to provide high rates of current discharge at lowtemperatures. Standby batteries are secondary batteries that use thick plates and thick separators to provide long life.Solidstate batteries can be constructed with unusual features and in irregular sizes and shapes. Size and weightreductions in all types of batteries continue to be made through use of new materials and methods of construction.

Selection and applicationsBatteries are probably the most reliable source of power known. Most critical electrical circuits are protected in somemanner by battery power. Since a battery has no moving parts, tests, calculations, or comparisons are made to predict theconditions of the cells in some batteries. Growing battery usage reflects the increased demand for portable computers;mobile voice, data, and video communications; and new or redesigned/repowered products in the consumer, industrial, and



transportation sectors. Further growth may result from significant increases in dc system operating voltage, such as from12 V to 24 V or 48 V, which can provide much higher power generally with less weight, greatly broadening the range ofpotential battery applications.

For most applications, the basic choice in selection is whether to use either a primary (nonrechargeable) or a secondary(rechargeable) cell or battery. Electrical characteristics affecting selection include maximum and minimum voltage, currentdrain, and pulse current (if any), its duration and frequency of occurrence. Other factors such as performance in thespecific application, operating environment, and final packaging of the cell or battery also must be considered.

P r im a r y b a t t e r y u s a g e

Primary batteries are used as a source of dc power where the following requirements are important:

1.

Electrical charging equipment or power is not readily available.

2. Convenience is of major importance, such as in a hand or pocket flashlight.

3. Standby power is desirable without cell deterioration during periods of nonuse for days or years. Reserveelectrolytedesigns may be necessary, as in torpedo, guided missile, and some emergency light and power batteries.

4. The cost of a discharge is not of primary importance.

Se c o n d a r y b a t t e r y u s a g e

Secondary batteries are used as a source of dc power where the following requirements are important:

1.

The battery is the primary source of power and numerous dischargerecharge cycles are required, as in wheelchairs andgolf carts, industrial hand and forklift trucks, electric cars and trucks, and boats and submarines.

2. The battery is used to supply large, shorttime (or relatively small, longertime), repetitive power requirements, as inautomotive and aircraft batteries which provide power for starting internal combustion engines.

3. Standby power is required and the battery is continuously connected to a voltagecontrolled dc circuit. The battery is saidto “float” by drawing from the dc circuit only sufficient current to compensate automatically for the battery's own internalselfdischarge. Computers and communications networks and emergency light and power batteries are in this category.

4. Long periods of lowcurrentrate discharge followed subsequently by recharge are required, as in marine buoys andlighthouses, and instrumentation for monitoring conditions such as earthquakes and other seismic disturbances.

5. The very large capacitance is beneficial to the circuit, as in telephone exchanges.

RatingsTwo key ratings of a cell are its voltage and amperehour (Ah) capacity. The voltage is determined by the chemical systemcreated by the active materials used for the negative and positive electrodes (anode and cathode). The amperehourcapacity is determined by the amount of the active materials contained in the cell. The product of these terms is the energyoutput or watthour capacity of the battery. In actual practice, only onethird to onehalf of the theoretical capacity may beavailable. Battery performance varies with temperature, current drain, cutoff voltage, operating schedule, and storageconditions prior to use, as well as the particular design.



Many primary batteries are rated by average service capacity in milliamperehours (mAh). This is the number of hours ofdischarge that can be obtained when discharging at a specified temperature through a specified fixed resistance to aspecified final or cutoff voltage, which is either at the point of rapid voltage drop or at minimum usable voltage.

Secondary batteries, such as automotive batteries, have been rated by amperehour capacity. Typically, this is the amountof current that the battery can deliver for 20 h without the temperaturecorrected cell voltages dropping below 1.75 V percell. A battery capable of giving 2.5 A for 20 h is rated at 50 amperehours at the 20h rate. This same battery may providean enginecranking current of 150 A for only 8 min at 80°F (27°C) or for 4 min at 0°F (−18°C), giving a service of only 20and 10 amperehours, respectively. By multiplying amperehours by average voltage during discharge, a more practicalwatthour rating is obtained. Automotive batteries also are rated by reserve capacity (RC) and coldcranking amps (CCA).Reserve capacity is the length of time that a fully charged battery at 80°F (27°C) can deliver 25 amperes before the voltagefalls to 10.5 V. A typical rating is 125 min, which is the length of time the battery could carry a minimum electrical load afterfailure of the vehicle's charging system. Coldcranking amps is a measure of the ability of a battery to crank an enginewhen the battery is cold. It is measured by the number of amperes that a 12 V battery can deliver for 30 s when it is at 0°F(−18°C) without the battery voltage falling below 7.2 V. A typical CCA rating for a battery with a reserve capacity of 125 minis 430 amperes. The CCA rating for most automobile batteries is between 300 and 600 amperes.

LifeThe life expectancy of a cell or battery depends on its design and materials, as well as its application and operatingconditions. Life expectancy is measured by shelf life and service life. Shelf life is the expected time that elapses before astored battery becomes inoperative due to age or deterioration, or unusable due to its own internal selfdischarge. Servicelife is the expected length of time or number of dischargecharge cycles through which a battery remains capable ofdelivering a specified percentage of its capacity after it has been put into service. This can vary from the one shot or singledischarge obtainable from primary cells to 10,000 or more dischargecharge cycles obtainable from some secondarybatteries. Automotive batteries may last as little as 18 months in hot climates and 10–12 years in cold climates, but typicallythey have an average life of 3 years and may last for 6000 cycles. Industrial batteries have a 10–20year service life.Standby sizes may be expected to float across the dc bus 8– 30 years. Generally the most costly, largest, and heaviestcells have the longest service life.

Many batteries experience an abrupt loss of voltage without warning when the active materials are depleted. However, insome batteries, opencircuit voltage serves as a stateofcharge indicator, decreasing slightly but continuously with loss ofcapacity. Many electronic devices now include a battery that will last for the life of the product. This eliminates the need forthe consumer or user to replace the battery and risk causing damage to the device or the battery by inadvertently shortingthe terminals, reversing the polarity, or installing a similarsize battery having the wrong chemistry.

To obtain the maximum life and ensure reliability of batteries, the manufacturer's recommendations for storage andmaintenance must be followed. The stated shelf life and temperature of primary cells must not be exceeded. For dryreserveelectrolyte primary cells and secondary cells of the dry construction with charged plates, the cell or batterycontainer must be protected against moisture, and storage must be within specified temperature limits. Wet, chargedsecondary batteries may require periodic charging and water addition, depending upon the construction.

Primary Batteries



A primary cell or battery is not intended to be recharged and is discarded when it has delivered all its electrical energy (Fig.1). Several kinds of primary cell are widely used, particularly in portable devices and equipment, providing freedom from thedependence on alternatingcurrent line power. They are convenient, lightweight, and usually relatively inexpensive sourcesof electrical energy that provide high energy density (long service life) at lowtomoderate or intermittent discharge rates,good shelf life, and ease of use while requiring little or no maintenance.

Fig. 1 Diagram of a zincalkalinemanganese dioxide cylindrical cell.

Primary cells are classified by their electrolyte, which may be described as aqueous, nonaqueous, aprotic, or solid. In mostprimary cells the electrolyte is immobilized by a gelling agent or mixed as a paste, with the term “dry cell” commonly appliedto the zinccarbon Leclanche cell and sometimes to other types. An aqueous electrolyte or electrolyte system is used inzinccarbon, magnesium, alkalinemanganese dioxide, mercuric oxide, silver oxide, and zincair cells. Nonaqueouselectrolyte systems are used in lithium cells and batteries. See also: Electrolyte (/content/electrolyte/221800)

Typical characteristics of different types of primary batteries and their applications are summarized in Table 1. Performancecharacteristics of primary batteries at various temperatures are shown in Fig. 2.

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Fig. 2 Performance characteristics of primary batteries at various temperatures.

Zinccarbon cellsThe zinccarbon or LeClanche dry cell was invented in 1866 and continues to be popular. It is made in sizes of varyingdiameter and height, and batteries are available in voltages ranging from 1.5 to 510 V. Common cell construction uses thecylindrical zinc container or can as the negative electrode and manganese dioxide (mixed with carbon black to increaseconductivity and retain moisture) as the positive active material, with the electrical connection made through a centercarbon electrode. The slightly acidic electrolyte is an aqueous solution of ammonium chloride and may also contain zincchloride, immobilized in a paste or the paper separator. The electrochemical reaction between the cathode, anode, andelectrolyte in a zinccarbon LeClanche cell is shown in reaction (1 ).(075200#075200RX0010)



Typical opencircuit voltage of a fresh LeClanche cell is over 1.55 V. The closedcircuit voltage gradually declines as afunction of the depth of discharge.

Significant improvements in capacity and shelf life of zinccarbon batteries have been made through the use of new celldesigns, such as the paperlined cell, and new materials. Upgrading to the use of purer beneficiated manganese dioxideand an electrolyte that consists mainly of zinc chloride and water has created the heavyduty or zinc chloride cell. Itsconstruction is similar to the zinccarbon cell, but having an anode of highpurity zinc alloy and typically a higher proportionof carbon to manganese dioxide and a greater volume of slightly more acidic electrolyte. The electrochemical reaction in azinc chloride cell is shown in reaction (2 ).(075200#075200RX0020)

Opencircuit voltage of a fresh zinc chloride cell typically is over 1.60 V. As in the LeClanche cell, closedcircuit voltagegradually declines as a function of the depth of discharge.

Compared to zinccarbon batteries, zinc chloride batteries have improved highrate and lowtemperature performance andare available in voltages ranging from 1.5 to 12 V. A common design is the flat cell, used in multicell batteries such as the 9V battery, which offers better volume utilization and, in some designs, better highrate performance. Characteristics ofstandard zinccarbon and zinc chloride cells are given in Table 2.

Magnesium cells

(1)

(2)



The magnesiumcarbon primary cell is basically a cylindrical zinccarbon cell in which the can or container is made ofmagnesium or its alloy instead of zinc. Magnesium has a greater electrochemical potential than zinc, providing an opencircuit voltage of about 2.0 V. Developed for military use in radios and other equipment, the magnesium cell has twice thecapacity or service life of a zinccarbon cell of equivalent size, and longer shelf life, particularly at elevated temperatures.However, when the load is applied to a magnesium cell, a characteristic voltage drop occurs briefly before the cell recoversto its usable voltage. This may make the magnesium cell unacceptable for use in some applications. The magnesium cellhas a vent for the escape of hydrogen gas, which forms during discharge.

Alkalinemanganese dioxide cellsThese cells became the most popular battery during the 1980s. Available in voltages ranging from 1.5 to 12 V and in avariety of sizes and shapes, they have higher energy density, better lowtemperature and highrate performance, andlonger shelf life than a zinccarbon battery. Alkaline and zinccarbon cells are chemically similar, both using zinc for theanode and manganese dioxide for the cathode active materials. However, the cells differ significantly in construction,electrolyte, and formulation of the active materials.

The container for the cylindrical alkaline cell is a steel can that does not participate in the electrochemical reaction. A gelledmixture of zinc powder and electrolyte is used for the anode. The highly alkaline electrolyte is an aqueous solution ofpotassium hydroxide, which is more conductive than the salt of the zinccarbon cell. The cathode is a highly compacted,conductive mixture of highpurity manganese dioxide and graphite or carbon. To prevent contact between the anode andcathode, which would result in a very active chemical reaction, a barrier or separator is placed between the two. A typicalseparator is paper or fabric soaked with electrolyte. The separator prevents solidparticle migration, while the electrolytepromotes ionic conductivity. The electrochemical reaction in an alkalinemanganese dioxide cell is shown in reaction (3

).(075200#075200RX0030)

Opencircuit voltage of a fresh cylindrical alkaline cell typically is 1.58 V. Closedcircuit voltage gradually declines as afunction of the depth of discharge.

Modifying the internal design of zincalkaline cells has resulted in cells that have an average of 20–50% higher amperehourcapacity or service life. This newer cell design provides a significantly greater volume for the active materials, the factormost responsible for improved performance. The modified cell is manufactured with a nickelplated steel can and anoutside poly(vinyl chloride) jacket (Fig. 1). A diaphragm vent is incorporated into the assembly in case of pressure buildup.Alkalinemanganese dioxide cells also are made in miniature sizes with flat, circular pellettype cathodes and homogeneousgelled anodes.

Mercuric oxide cellsThe zincmercuric oxide cell (Fig. 3) has high capacity per unit charge, relatively constant output voltage during discharge,and good storage qualities. It is constructed in a sealed but vented structure, with the active materials balanced to preventthe formation of hydrogen when discharged. Three basic structures are used: the wound anode, the flat pressedpowderanode, and the cylindrical pressedpowder electrode. Typically, the anode is zinc, the cathode is mercuric oxide, and theelectrolyte is alkaline. The electrochemical reaction in a mercuric oxide cell is shown in reaction (4

).

(3)

(075200#075200RX0040)

(4)



Opencircuit voltage of a mercuric oxide cell is 1.35 V, with some batteries delivering up to 97.2 V.

Fig. 3 Diagram showing the design of a mercury button cell.

Mercuric oxide batteries have been made in various sizes and configurations, from the miniature button 16 mAh to thelarge 14 Ah cylindrical cell, and are suited for use at both normal and moderately high temperatures. However, the lowtemperature performance is poor, particularly under heavy discharge loads. Use at temperatures below 32°F (0°C) isgenerally not recommended. Mercuric oxide batteries have been used for hearing aids, cameras, watches, calculators,implanted heart pacemakers and other medical applications, emergency radios, and military equipment. Today concernsabout health hazards and environmental regulations related to disposal generally prevent manufacture and sale of mercuricoxide batteries. They are replaced with newer, less expensive designs such as zincair that do not contain mercury or itscompounds.

The cadmiummercuric oxide battery is similar to the zincmercuric oxide battery. The substitution of cadmium for the zincanode lowers the cell voltage but offers a very stable system, with a shelf life of up to 10 years, and improved performanceat low temperatures. Its watthour capacity, because of the lower voltage, is about 60% of the zincmercuric oxide battery.However, health concerns and environmental regulations related to disposal also limit the availability and usage of batteriescontaining cadmium.

Silver oxide cellsThe zincsilver oxide primary cell is similar to the zincmercuric oxide cell, but uses silver oxide in place of mercuric oxide(Fig. 3). This results in a higher cell voltage and energy. In the small buttoncell configuration, this is a significant advantagefor use in hearing aids, photographic applications, watches, and calculators. The silver oxide battery has a higher voltagethan a mercury battery; a flatter discharge curve than an alkaline battery; good resistance to acceleration, shock, andvibration; an essentially constant and low internal resistance; and good performance characteristics at temperatureextremes.



Silver oxide batteries generally have a flat circular cathode and a homogeneous gelled anode. The cathode is a mixture ofsilver oxide with a low percentage of manganese dioxide and graphite, and the anode is a mixture of amalgamated zincpowder. A highly alkaline electrolyte of either sodium hydroxide or potassium hydroxide is used, although potassiumhydroxide makes the battery more difficult to seal. The separator is a material that prevents migration of any solid particlesin the battery.

The chemical reaction in a silver oxide cell is shown in reaction (5 ).(075200#075200RX0050)

Opencircuit voltage of a silver oxide cell is 1.6 V, with batteries available having a nominal voltage of 6 V.

Zincair cellsZincair cells (Fig. 4) have the highest energy density of the commercially available primary cells. They use atmosphericoxygen for the active cathode material, so there is no need to include the cathode material in the cell. This allows thecathode electrode to be very thin. The remaining space can be used for increasing the amount of zinc, which is the activeanode material, resulting in a higher cell capacity (Fig. 4a).

Fig. 4 Zincair cell. (a) Cross section compared with metal oxide cell. (b) Major components.

The zincair cell is usually constructed in a button configuration (Fig. 4b). The cell consists of two cans, isolated from eachother by an annular insulator. One can contains the zinc anode and the other the air or oxygen cathode. The anode can isfabricated from a triclad metal; the external material is nickel for good electrical conductivity, the middle layer is stainlesssteel to provide strength, and the inner surface is copper, which is compatible with the cell components. The cathode can isfabricated of nickelplated steel and contains holes that allow air to enter the cell. A layer of permeablepolytetrafluoroethylene (Teflon) serves as a separator to assure the proper distribution of air and limit the entrance or exitof moisture. The anode is an amalgamated gelled zinc powder and electrolyte. Although the cathode uses atmosphericoxygen as the active material, a mixture of carbon, polytetrafluoroethylene, and manganese dioxide is impressed on anickelplated screen. The carbon and manganese dioxide serve as catalysts for the oxygen reaction. The electrolyte is anaqueous solution of potassium hydroxide with a small amount of zinc oxide.

(5)



The air holes of the zincair cell are sealed until the cell is used, to inhibit the entrance of air. In this condition, the cells canretain more than 95% of their rated capacity after 1 year of storage at room temperature. The cells are activated byremoving the seal which permits the flow of air into the cell. The chemical reaction in a zincair cell is shown in reaction (6

).(075200#075200RX0060)

\noindent The opencircuit voltage of a zincair cell is about 1.4 V, providing a flat discharge with the operating voltagebetween 1.35 and 1.1 V, depending on the discharge conditions. The cell is capable of low to moderately high dischargerates, and is used in applications requiring a relatively short operating time before replacement.

Zincair cells are manufactured in sizes from 50 to 6500 mAh. Multicell batteries are available in a wide range of voltageand capacity ratings, including a nominal 8.4V zincair battery that is interchangeable in some applications with the zincchloride and alkaline 9V battery.

Lithium cellsLithium is a silverywhite element that is the lightest metal, having a density only about half that of water, with which thealkaline lithium is highly reactive. Lithium has good conductivity, and its standard potential and electrochemical equivalenceare higher than those of any other metal. It is widely used in various forms as battery anode material (negative electrode),especially in coinsize primary cells. There are several different types of lithium cells, primary as well as reserve andsecondary, similar to the variety of cells using a zinc anode. Each type of lithium cell differs in the cathode material for thepositive electrode, electrolyte, and cell chemistry as well as in physical, mechanical, and electrical features (Table 3).Performance advantages of lithium cells over other primary cells include high voltage (may be above 3 V), high energydensity, operation over a wide temperature range, and long shelf life. Lithium cells are manufactured in different sizes andconfigurations, ranging in capacity from milliamperehours to over 20,000 Ah, with characteristics matched to the generalapplication. See also: Lithium (/content/lithium/387000)

Table 3 Classification of lithium primary cells*

Cellclassification

Typicalelectrolyte

Powercapability Size, Ah

Operatingrange, °F (°C)

Shelflife,years

Typicalcathodes

Nominal cellvoltage, V

Keycharacteristics

Solublecathode Organic or

Moderateto 0.5−20,000 −67 to 158 5−10 Sulfur dioxide 3.0

High energyoutput;

(liquid orgas) inorganic

highpower, (−55 to 70) Thionylchloride 3.6

high poweroutput;

(w/solute) W Sulfurylchloride 3.9

lowtemperature

operation;long shelf life

Solid cathode Organic Low to 0.03−5 −40 to 122 5−8 Silver chromate 3.1 High energyoutput for

(w/solute) moderate (−40 to 50) Manganesedioxide 3.0

moderatepower

(6)

power,mW Carbonmonofluoride 2.6 requirements;

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Table 3 Classification of lithium primary cells

Copper(I)sulfide 1.7

nonpressurizedcells

Iron disulfide 1.6 Iron sulfide 1.5

Copper(II)oxide 1.5

Solidelectrolyte Solid state Very low 0.003−0.5 32 to 212 10−25

I2poly(2vinylpyridine) 2.8

Excellent shelflife;

power,μW (0 to 100)

solidstate—no

leakage;longterm

microampere

discharge*From D. Linden (ed.), Handbook of Batteries and Fuel Cells, McGrawHill, 2d ed., 1995.

In a lithium cell, nonaqueous solvents must be used for the electrolyte because of the solubility and reactivity of lithium inaqueous solutions. Organic solvents, such as acetonitrile and propylene carbonate, and inorganic solvents, such as thionylchloride, are typical. A compatible solute is added to provide the necessary electrolyte conductivity. Solidcathode cells aregenerally manufactured as cylindrical cells in sizes up to about 30 Ah in both low and highrate constructions. The lowrate,or highenergy, designs use a bobbintype construction to maximize the volume for active materials (Fig. 5a). These cellshave the highest energy density of cells of similar size. The highrate cells use a jellyroll (spiralwound) construction, whichprovides the large electrode surface required for the high discharge rates (Fig. 5b). These cells deliver the highest rates ofall primary batteries and are widely used in military applications. Early ambienttemperature lithium systems used lithiumsulfur dioxide chemistry, and found applications in medical implants, weapons systems, and spacecraft. These cells provide3 V and have seven times the energy of a typical alkaline battery. However, other lithium chemistry has been developed.Four types of cells are lithiumcarbon monofluoride, lithiummanganese dioxide, and lithiumiron disulfide, all of which havesolid cathodes, and lithiumthionyl chloride, which has a liquid cathode.

Fig. 5 Solid cathode cells. (a) Lithiummanganese dioxide bobbin cell. (b) Lithiummanganese dioxide spiralwound cell.(Duracell, Inc.)



Lithiumcarbon monofluoride batteries have a solid carbon monofluoride cathode and characteristics that allow the batteryto be used for the life of the product in which the battery is installed, such as computer realtime clock and memory backupapplications, instead of having scheduled replacement intervals. The cell has a storage and operational temperature rangeof −40 to +85°C, and a long life made possible by a selfdischarge rate that may be less than 0.2% of capacity loss peryear. As a lithiumcarbon monofluoride cell discharges while powering a specified load, internal resistance generallyremains low and level while the closedcircuit voltage profile remains high, flat, and stable until the depth of dischargeexceeds approximately 85%. When completely discharged, this type of lithium cell may be disposed of as nonhazardouswaste. Batteries containing unreacted lithium metal are considered reactive hazardous waste and must be disposed offollowing the applicable local, state, and federal regulations.

Lithiummanganese dioxide cells have a solid manganese dioxide cathode and characteristics that make the preferred useof the cell to be where periodic replacement is routinely performed. The cell can supply both pulse loads and very smallcurrent drains, typical needs for microprocessor applications. As the cell discharges, its internal resistance increasesbecause of the manganese dioxide, causing a tapered discharge profile and a declining closed circuit voltage. Themanganese dioxide also limits the maximum temperature rating of the cell to 140°F (60°C), a temperature at which selfdischarge may increase to a rate of over 8% per year. However, the cell costs less than a lithiumcarbon monofluoride cell,and is widely used especially for applications requiring intermittent pulsing such as remote keyless entry systems. Whencompletely discharged, this type of lithium cell may be disposed of as nonhazardous waste.

Lithiumiron disulfide cells have an anode of lithium foil in contact with a stainlesssteel can and a cathodematerial mixtureof graphite and iron disulfide. These cells have an opencircuit voltage of 1.8 V, a nominal voltage of 1.5 V, and can be usedin any application that uses other AAsize 1.5V batteries. Each battery contains two safety devices: a thermal switch whichacts as a current limiter if the battery begins to overheat, and a pressurerelief vent that opens at a predeterminedtemperature. This type of lithium cell may be disposed of using the same procedures approved for other cells.

Lithiumthionyl chloride cells were designed for the military and have been used for nuclear surety applications, whichrequire longlife power sources for command and control systems. These cells have a voltage of about 3.6 V, makingpossible the use of fewer cells for the same application. They are classed as highenergy, highcurrentdrainrate cells, withtwice the energy density of lithiumsulfur dioxide cells, and will last twice as long. Lithiumthionyl chloride cells have asoluble cathode which is liquid, toxic, and corrosive. Each cell is hermetically sealed, with a designedin fuse to avoidrupture or explosion if the battery is inadvertently charged or shorted. A lithiumthionyl chloride cell should be replaced onlyby a trained technician. Because thionyl chloride is highly toxic and corrosive, this battery is an environmental hazard whichrequires special handling and disposal.

Solidelectrolyte cellsThese may be classified as (1) cells using a solid crystalline salt (such as lithium iodide) as the electrolyte and (2) cellsusing a solidpolymer electrolyte. With either type of electrolyte, the conductivity must be nearly 100% ionic as anyelectronic conductivity causes a discharge of the cell, which limits shelf life. Solidpolymer electrolytes are based on thecharacteristic that solutions of alkali metal salts dissolved in certain polymers, such as poly(ethylene oxide), form solidpolymers that have reasonable ionic conductivity. The solid polymers can be fabricated in thin cross sections, are morestable than liquid electrolytes, and can serve as the separators. Most development work on thinfilm polymer electrolytebatteries has been for rechargeable batteries, using a lithium anode and solid cathode materials. Energy densities of 5–10times that of leadacid cells have been calculated. The technology can also be applied to the design of primary cells andbatteries. See also: Electrolytic conductance (/content/electrolyticconductance/221900); Ionic crystals(/content/ioniccrystals/352100)

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The most widely used solidelectrolyte cells have lithium iodide as the solid electrolyte. These batteries have a solid lithiumfoil anode and a cathode that is largely iodine. The iodine is made conductive by the addition of an organic compound,poly(2vinylpyridine). This iodinepolyvinylpyridine cathode has a tarlike consistency in the fresh battery, then solidifiesgradually as the battery is discharged. Lithium and iodine are consumed during the discharge, and the reaction product,lithium iodide, forms in place in the region between the two reactants where it serves as the cell separator. Because theelectrolyte continues to form as the battery discharges, the overall resistance of the cell continually increases withdischarge. This results in a drop in cell voltage for a given current drain. The nominal cell voltage is around 2.8 V. Thesebatteries have a very low rate of selfdischarge, a long storage life, and high reliability, but can be discharged only at lowrates because of the low conductivity of the electrolyte. Applications for these batteries include memory backup andimplanted cardiac pacemakers.

A typical implantable battery has a volume of 0.4 in.3 (6 cm3), weighs 0.8 oz (23 g), and has a 2 Ah capacity. The lifetime ofthis battery is 5–10 years since pacemakers typically draw only 1530 microamperes. The battery is considered to bedischarged when the output voltage drops to 1.8 V. This may be detected by monitoring the patient's pulse rate. See also:Medical control systems (/content/medicalcontrolsystems/412800)

Cells that use only solid components, including an ionconducting solid electrolyte, are called solidstate cells or batteries.Some of these have electrodes made of fastion conductors, materials that are good conductors for both ions andelectrons. Examples include the layeredstructure disulfides of titanium and vanadium, TiS2 and VS2, which can be used asthe cathode or sink for lithium, and aluminumlithium alloys, which can be used as the anode or source of lithium in lithiumbatteries. These materials can sustain high reaction rates because of their unique crystalline structures which allow theincorporation of ions into their crystalline lattices without destruction of those lattices. See also: Energy storage(/content/energystorage/233100); Intercalation compounds (/content/intercalationcompounds/348250); Solidstate chemistry (/content/solidstatechemistry/634800)

In a solidstate cell, the polycrystalline pressed electrolyte is interspaced between a metallic anode and the solid cathodematerial. The electrodes are applied to the electrolyte by mechanically pressing the materials together, or in some casesthe electrolyte is formed in place by reaction between the two electrodes. These cells are then stacked together to form abattery of the required voltage. A carbon current collector is often used on the cathode side, and this is frequently admixedwith the cathode material. If the cathode material is sufficiently conductive, for example titanium disulfide, no carbonconductor is needed.

Reserve batteriesMost primary batteries are ready for use at the time of manufacture. However, highenergy primary batteries are oftenlimited in their application by poor charge retention resulting from selfdischarge between the electrolyte and the activeelectrode materials. The use of an automatically activated battery, or reserve battery, can overcome this problem,especially when the battery is required to produce high currents for relatively short periods of time (seconds or minutes),typical of military applications. A reserve battery is manufactured as a complete but inert battery that is stored in an inactivecondition by keeping one of the critical cell components, such as the electrolyte, separated from the rest of the battery. Thebattery is activated just prior to use by adding this component manually or automatically. An important design considerationis to ensure that the electrolyte or other withheld component is delivered as quickly as possible at the time of activationwhile avoiding chemical shortcircuiting of the cells.

Zincsilver oxide reserve batteries

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Automatically activated batteries have been used in missile and spacecraft applications, where the battery has to beactivated from a remote source. The package contains a mechanism that drives the electrolyte out of the reservoir and intothe cells of the battery. Most of these automatically activated batteries use zincsilver oxide chemistry with a solution ofpotassium hydroxide for the electrolyte in order to achieve the required high discharge rates.

Magnesium wateractivated batteriesSeveral types of wateractivated (dunk type) batteries use magnesium anodes and silver chloride or cuprous chloridecathodes. The batteries are assembled dry, with the active elements separated by an absorbent. Activation occurs bypouring water into the battery container or by immersing the battery in water or seawater. Magnesiumsilver chloridebatteries have many marine applications, including buoys, beacons, flares, and safety lights. They also power the pingerswhich are attached to and help locate the cockpit voice recorder and flight data recorder in downed aircraft, and emergencylighting for submarine escape hatches. Magnesiumcopper iodide and magnesiumcuprous chloride batteries have similarcapabilities.

Lithiumanode reserve batteriesSeveral types of batteries having a lithium anode are available as reserve batteries. These include batteries using lithiumsulfur dioxide, lithiumthionyl chloride, and lithiumvanadium pentoxide chemistry. Lithiumsulfur dioxide and lithiumthionylchloride reserve batteries may be gasactivated, with activation triggered by electrical, mechanical, or pressure signals. Thelithiumvanadium pentoxide battery is an electrolyteactivated battery. The electrolyte is contained in a glass ampule or vial,which is broken by mechanical shock, allowing the electrolyte to disperse within the cell.

Thermal batteriesA thermal battery, or fusedelectrolyte battery, is a type of reserve battery that is activated by the application of heat. Atroom temperature, the electrolyte is a solid and has a very low conductivity, rendering the battery essentially inert. Whenthe temperature is raised above the melting point of the electrolyte, the molten electrolyte becomes ionically conductive,and the battery is then capable of delivering electrical energy. Thermal batteries were introduced in 1955 to solve the wetstand time limitation of aqueous systems, and subsequently were used as the main power source for nuclear weaponsystems.

Early thermal batteries used calciumcalcium chromate chemistry. This was replaced in 1980 by thermal batteries that useda lithium anode, an iron sulfide cathode, and a lithium chloridepotassium chloride electrolyte. Figure 6 shows a typicalmulticell lithiumiron disulfide thermal battery, which is activated by an electrical pulse to an integral electric match (squib).Other thermal batteries are activated mechanically using a percussiontype primer. The principal means for heating arepyrotechnic heat sources such as zirconium barium chromate heat paper or a heat pellet containing fine iron powder andpotassium perchlorate. When the temperature rises to about 750°F (400°C), the electrolyte becomes molten andconductive. For other sources of electric energy known as batteries or cells See also: Fuel cell (/content/fuelcell/274100); Nuclear battery (/content/nuclearbattery/457900); Solar cell (/content/solarcell/633000)

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Fig. 6 Lithium/iron disulfide thermal battery. (Sandia National Laboratories)

Donald L. Anglin

Secondary BatteriesSecondary batteries (also known as accumulators) are rechargeable. This means that the electrochemical reactions in thecell must be reversible so that if the load in the external circuit is replaced by a power supply, the reactions in the cell canbe forced to run in reverse, thereby restoring the driving force for reaction and hence recharging the cell. In contrast,primary batteries cannot be recharged because the reactions that produce current cannot be made to run in reverse;instead, totally different reactions occur when the cell is forcibly charged, and in some instances the reaction products aredangerous, that is, explosive or toxic.

The paradigm of battery design is to identify a chemical reaction with a strong driving force and then to fashion a cell thatrequires the reaction to proceed by a mechanism involving electron transfer, thereby making electrons available to a load inthe external circuit. The magnitude of the driving force will determine cell voltage; the kinetics of reaction will determine cellcurrent.



There are many chemistries that will serve as the basis for secondary batteries. Distinctions can be made on the basis ofthe following metrics: voltage, current (maximum, steadystate, and peak), energy density (Wh/kg and Wh/L), power density(W/kg and W/L), service life (cycles to failure), and cost ($/kWh). Table 4 summarizes performance characteristics of someof the secondary battery types. Such comparisons are made difficult by the fact that many performance characteristics arefunctions of battery size and service conditions. For example, service life is greatly affected by depth of discharge anddischarge current. However, both of these operating parameters can be very different for two different battery types thatwere designed for very different applications.

Table 4 Comparison of performance characteristics of secondary batteries

Characteristics Pbacid NiCd NiMH ZnAg NaS Znair* Liion LiSPE†

Nominal voltage, V 2 1.2 1.2 1.5 1.9 1.5 3.6 3.6

Specific energy, Wh/kg 35 40 90 110 80 280 125 500

Specific energy, kJ/kg 126 144 324 396 288 1008 450 1800

Volumetric energy, Wh/L 70 100 245 220 385 440 900Volumetric energy, kJ/L 252 360 882 792 1386 1584 3240

*Based upon commercial prototype notebook computer battery. †Projections based upon thinfilm microbattery test results in the laboratory.

Another classification scheme considers the state of aggregation of the principal cell components, that is, whether theelectrolyte is a solid or liquid, and whether the electrode active material is a solid, liquid, or gas. Most batteries have solidelectrodes and a liquid electrolyte. However, there are examples of batteries in which the anode and cathode are bothliquid, and the electrolyte is solid.

What follows is a series of descriptions of the significant secondary battery chemistries.

Leadacid batteriesThe leadacid battery is the dominant secondary battery, used in a wide variety of applications, including automotive SLI(starting, lighting, ignition), traction for industrial trucks, emergency power, and UPS (uninterruptible power supplies). Theattributes of leadacid batteries include low cost, high discharge rate, and good performance at subambient temperatures.The first practical leadacid cell was made by Planté in France in 1860.

The anode is metallic lead. The cathode active material is lead dioxide, which is incorporated into a composite electrodealso containing lead sulfate and metallic lead. The electrolyte is an aqueous solution of sulfuric acid, 37% by weight whenthe battery is fully charged.

The halfcell reactions at each electrode are shown in reactions (7 ) and (8). The overall cell reaction is the formation of lead sulfate and water, shown in reaction (9). When the battery is discharging,

(075200#075200RX0070)(075200#075200RX0080)(075200#075200RX0090)

(7)

(8)

(9)the reactions proceed from left to right; upon charging, the reactions proceed from right to left. The elementaryelectrochemical reactions are shown in reactions (10 (075200#075200RX0100)) and (11 (075200#075200RX0110)). On



discharge, electrons are

\noindent produced at the anode as metallic lead is oxidized to Pb(II) present in lead sulfate; the complementary reaction atthe cathode is the reduction of Pb(IV) present in lead dioxide to Pb(II) present in lead sulfate with the attendantconsumption of electrons.

Sulfuric acid functions not only as the electrolyte but also as one of the reactants. Consequently, the acid concentration is afunction of the instant state of charge and attains maximum value when the battery is fully charged.

Nominal voltage is 2 V, which decreases as the battery is discharged. The lower limit is governed by the depth of discharge.The theoretical specific energy is 170 Wh/kg. Commercially available leadacid batteries deliver about 35 Wh/kg, which isabout 20\% of theoretical. However, leadacid batteries are capable of high specific power, have relatively flat dischargeprofiles, are comparatively insensitive to voltage changes with temperature, can be made for calendar lives exceeding 20years, and are the least costly of all rechargeable technologies. Thus, when mobility is not a consideration and hence thereis no penalty for the high density of lead, leadacid technology can be found. The disadvantages of leadacid technologyinclude low specific energy and possibility of hydrogen evolution.

Nickelcadmium batteriesThe nickelcadmium battery is the dominant alkaline secondary battery and is used in many of the same heavy industrialapplications as are leadacid batteries. At the same time, nickelcadmium batteries are found in applications requiringportable power such as electronics and power tools. The first nickelcadmium battery was made by Jungner in Sweden in1900.

The anode is metallic cadmium. The cathodeactive material is nickel oxide present as nickel oxyhydroxide (NiOOH). Theactive materials of both electrode are incorporated into porous sintered nickel plaques. The electrolyte is an aqueoussolution of potassium hydroxide, 31% by weight when the battery is fully charged.

The halfcell reactions at each electrode are shown in reactions (12 ) and (13). The overall cell reaction is the formation of nickel hydroxide and cadmium hydroxide, shown in

reaction (14 ). The

(075200#075200RX0120)(075200#075200RX0130)

(075200#075200RX0140)

(075200#075200RX0160)

(10)

(11)

(12)

(13)

(14)elementary electrochemical reactions are shown in reactions (15 ) and (16

). On discharge, electrons are produced(075200#075200RX0150)

(15)

(16)



\noindent at the anode as metallic cadmium is oxidized to Cd(II) present in cadmium hydroxide; the complementaryreaction at the cathode is the reduction of Ni(III) present in nickel oxyhydroxide to Ni(II) present in nickel hydroxide with theattendant consumption of electrons.

Nominal voltage is 1.2 V. The theoretical specific energy is 220 Wh/kg. Commercially available nickelcadmium batteriesdeliver about 40 Wh/kg, although cells with plasticbonded plates can achieve 55 Wh/kg. Nickelcadmium batteries arecapable of withstanding considerable mechanical abuse. They are also chemically quite stable owing to the fact that noneof the cell components is attacked by the electrolyte. The disadvantages of nickelcadmium technology include low specificenergy, and the socalled memory effect in which the cell loses capacity as it seemingly conforms to a duty cycle that doesnot involve full discharge.

Nickelmetal hydride batteriesThe nickelmetal hydride battery, commonly designated NiMH, is a comparatively new technology that has found uses inlaptop computers, cellular telephones, and other portable devices where high specific energy is sought. Larger cells havebeen built for use in electric vehicles.

The electrochemistry shares some features with the nickelcadmium battery. For example, the cathode active material isnickel oxyhydroxide. In contrast, the anode active material is hydrogen, which is present as the hydride of a proprietarymetal alloy. The electrolyte is an aqueous solution of potassium hydroxide, roughly 30% by weight.

The halfcell reactions at each electrode are shown in reactions (17 ) and (18). The overall cell reaction is the formation of nickel hydroxide and extraction of the hydrogen

storage alloy, shown in reaction (19 ).

(075200#075200RX0170)(075200#075200RX0180)

(075200#075200RX0190)

Here M denotes the hydrogen storage alloy and MH is the hydride compound of same. The elementary electrochemicalreactions are shown in reactions (20 ) and (21 ). On discharge,electrons are produced

(075200#075200RX0200) (075200#075200RX0210)

at the anode as hydrogen stored in the alloy is oxidized to protons, which combine with hydroxyl ions in the electrolyte toform water; the complementary reaction at the cathode is the reduction of Ni(III) present in nickel oxyhydroxide to Ni(II)present in nickel hydroxide with the attendant consumption of electrons.

Nominal voltage is 1.2 V. The theoretical specific energy is 490 Wh/kg. Commercially available nickelcadmium batteriesdeliver about 90 Wh/kg, which is substantially higher than nickelcadmium or leadacid batteries. However, materials costsassociated with the hydrogen storage alloy are high, and thus the final cost per unit charge ($/kWh) is higher for NiMH thanfor the other two cited technologies.

Silverzinc batteries

(17)

(18)

(19)

(20)

(21)



The silverzinc battery boasts the highest specific energy and specific power of any secondary battery containing anaqueous electrolyte. However, the high cost of silver has restricted the battery's use to military and aerospace applicationsprimarily.

The anode is metallic zinc. The cathode active material is silver oxide. The electrolyte is an aqueous solution of potassiumhydroxide, 45% by weight.

The discharge reaction occurs in two steps, shown in reactions (22 ) and (23). The overall cell reaction

(075200#075200RX0220)(075200#075200RX0230)

is the production of silver by metallothermic reduction of silver oxide by zinc. The elementary electrochemical reactions areshown in reactions (24 ), (25 ), and (26 ). Ondischarge, electrons are

(075200#075200RX0240) (075200#075200RX0250) (075200#075200RX0260)

produced at the anode as zinc is oxidized to Zn(II) present as zinc oxide; the complementary reactions at the cathode arethe reduction of Ag(II) present in silver oxide first to Ag(I) present in Ag2O, followed by the reduction of Ag(I) to metallicsilver, each step accompanied by the attendant consumption of electrons.

Nominal voltage is 1.5 V. The theoretical specific energy is 590 Wh/kg. Commercially available nickelcadmium batteriesdeliver about 120 Wh/kg. However, silverzinc suffers from the high costs associated with silver, loss of cathode activematerial through dissolution of silver oxide in the electrolyte, and cell shorting by zinc dendrites on charging, all of whichlead to poor cycle life. However, when huge currents are needed (and cost is no object), silverzinc is the battery of choice.

Sodiumsulfur batteriesThe sodiumsulfur battery is unique in several ways. Most batteries have solid electrodes and a liquid electrolyte; thesodiumsulfur battery has molten electrodes separated by a solid membrane serving as the electrolyte. In order to keep theelectrodes molten and the electrolyte sufficiently conductive, superambient temperatures are required; the sodiumsulfurbattery operates at 300°C (572°F). Sodiumsulfur batteries were once prime candidates for electric vehicle power sourcesand electric utility energy storage for load leveling. However, in recent years, commercial production has ceased.

The electrolyte is a Ushaped tube made of the ceramic material aluminum oxide, specifically β″Al2O3 which is a sodiumion conductor. The tube is filled with molten metallic sodium which is the anode active material. A metal rod immersed in thesodium serves as current collector. The anode/electrolyte assembly in positioned inside a larger metal container. The spacebetween the metal container and the ceramic electrolyte tube is occupied by carbon felt filled with elemental sulfur which isthe cathode active material. The cathode current collector is the carbon felt which is in electrical contact with the outermetal container.

(22)

(23)

(24)

(25)

(26)



The halfcell reactions at each electrode are shown in reactions (27 ) and (28). The overall cell reaction is the formation of sodium sulfide, shown in reaction (29).

(075200#075200RX0270)(075200#075200RX0280)(075200#075200RX0290)

The elementary electrochemical reactions are identical to the above. The key to the cell's operation is the fact that β″Al2O3acts as a separator to prevent direct contact of molten sodium and sulfur while allowing only Na+ to pass from the anodechamber to the cathode chamber.

On discharge, electrons are produced at the anode as metallic sodium is oxidized to Na(I) present in the β″Al2O3electrolyte as free sodium ions; the complementary reaction at the cathode is the reduction of elemental sulfur to S(II)present as polysulfide ion which reacts immediately to form sodium sulfide. The sodium ions are delivered to thecathode chamber by the solid electrolyte. Thus, as the cell discharges, the sulfur content of the cathode chamberdecreases and the sodium sulfide concentration rises.

Nominal voltage is 1.9 V. The theoretical specific energy is 750 Wh/kg. The last commercially available sodiumsulfurbatteries delivered about 80 Wh/kg. While sodiumsulfur batteries have performance characteristics comparable to the bestbatteries with aqueous electrolytes, thermal management requirements (keeping the cell at temperature) and theindeterminacy of the mode of failure, which in turn lead to safety concerns, have limited the successful deployment of thisbattery technology.

Zincair batteriesThe combination of a metal anode and an air electrode results in a battery with an inexhaustible supply of cathode reactant.Recharging involves restoring the anode either electrochemically or mechanically, that is, by direct replacement. Inprinciple, extremely high specific energies should be attainable as the theoretical energy density is 1310 Wh/kg.

The anode is metallic zinc. The cathode active material is oxygen, which is present as a component of air. The currentcollector is highsurfacearea carbon. The electrolyte is an aqueous solution of potassium hydroxide 45% by weight, whichmay be gelled to prevent leakage.

The halfcell reactions at each electrode are shown in reactions (30 ) and (31). The overall cell reaction is the oxidation of zinc to form tetrahydroxyzincate

(075200#075200RX0300)(075200#075200RX0310) orzinc oxide, depending upon the instant composition of the electrolyte, shown in reaction (32 ).When the concentration

(075200#075200RX0320)

(27)

(28)

(29)

(30)

(31)

(32)

2−



of Zn(OH) 2−4 exceeds the solubility limit, precipitation of zinc oxide occurs according to reaction (33). Under(075200#075200RX0330)

these conditions the overall reaction is effectively the oxidation of zinc according to reaction (34 ).The

(075200#075200RX0340)

elementary electrochemical reactions are shown in reactions (35 ) and (36). On discharge,

(075200#075200RX0350)(075200#075200RX0360)

electrons are produced at the anode as zinc is oxidized to Zn(II) present as or zinc oxide; the complementaryreaction at the cathode is the reduction of oxygen present in air to O(II) present in hydroxide.

Nominal voltage is 1.5 V. For applications such as notebook computers demonstration cells have been built that deliver 280Wh/kg. Other attributes include a relatively flat discharge curve, long shelf life thanks to water activation (battery is stored“dry”), and visual inspection of anode condition to determine state of charge. Among the disadvantages is the complexity ofa system that comprises a solid anode, liquid electrolyte, and a gaseous cathode. Because the oxygen electrode does notstand up well to operation as an anode (which must happen on charging), a third electrode must be incorporated into thecell. Alternatively, provision must be made for easy disassembly for replacement of a fresh zinc anode and subsequentflawless reassembly of the “recharged” battery.

Lithiumion batteriesThe lithiumion battery is fast becoming the dominant battery in applications requiring portable power such as electronicsand power tools. As such, it is displacing nickelcadmium and nickelmetal hydride from some of their traditional uses.

The term “lithiumion” derives from the fact that there is no elemental lithium in the battery; instead, lithium shuttlesbetween hosts, a behavior that has earned this battery the nickname “rocking chair.” In the anode, the chemical potential oflithium is high, that is, desirably near that of pure lithium; in the cathode, the chemical potential of lithium is low. The anodeis a carbonaceous material (graphite or coke) chosen for its electronic conductivity and its ability to intercalate lithium atpotentials near that of pure lithium. An example is LiC6. In commercial cells the cathode active material is a lithiatedtransitionmetal oxide such as lithium cobalt oxide. Because lithium is more electropositive than hydrogen, the electrolytemust be nonaqueous and aprotic. A representative formulation is a solution (1:1 by volume) of ethylene carbonate andpropylene carbonate containing a suitable lithium salt (at a concentration of about 1 M) such as lithiumhexafluorophosphate, LiPF6, which has been introduced in order to raise the conductivity of the electrolyte. For safety, aseparator made of a polyolefin such as microporous polypropylene is placed between the electrodes. If the electrolytetemperature exceeds a certain value, the separator melts and current flow ceases.

The halfcell reactions at each electrode are shown in reactions (37 ) and (38).

(075200#075200RX0370)(075200#075200RX0380)

(33)

(34)

(35)

(36)

(37)



The overall cell reaction is the formation of lithium cobalt oxide, shown in reaction (39 ). The (38)elementary electrochemical reactions are shown in reactions (40 ) and (41

).

(075200#075200RX0390)(075200#075200RX0400)

(075200#075200RX0410)

On discharge, electrons are produced at the anode as elemental lithium is oxidized to Li(I) present in the electrolyte as freelithium ions; the complementary reaction at the cathode is the reduction of Co(IV) to Co(III) with the attendant consumptionof electrons. Note that lithium intercalates into carbon as Li0, a neutral species, whereas lithium intercalates into LiCoO2 asLi+, a charged species. However, the presence of Li+ in the cathode triggers a valence shift in the host itself: thecompensating electron does not neutralize Li+ but is localized on Co4+, converting it to Co3+.

Nominal voltage is 3.6 V. The theoretical specific energy of this cell fitted with a LiCoO2 as cathode active material is 770Wh/kg. Commercially available lithiumion batteries deliver about 125 Wh/kg.

Lithiumsolid polymer electrolyte (SPE) batteriesSince the 1970s it has been known that, upon addition of appropriate salts, polymers can be rendered lithiumionconductors. Such materials can serve as electrolytes in lithium batteries. When full measure is given to the capacity forminiaturization of a fully solidstate battery, it becomes evident that, in principle, this has the potential to attain the highestspecific energy and specific power of any rechargeable technology. In addition, a lithiumSPE battery offers otheradvantages: ease of manufacture, immunity from leakage, suppression of lithium dendrite formation, elimination of volatileorganic liquids, and mechanical flexibility. It is this last attribute that makes lithiumSPE batteries most intriguing: a multilayerlaminate of thin films of metal, polymer, and ceramic measuring some tens of micrometers in thickness, totally flexible, witha specific energy in excess of 500 Wh/kg and capable of delivering power at rates in excess of 1000 W/kg at roomtemperature, operable over a temperature range from −30°C to +120°C, and costing less than $500/kWh. Realizationawaits advances in research in materials science and battery engineering.

OutlookWhat is in store for secondary power sources, remains speculative. Perhaps highercapacity batteries for automobiletraction will be developed. There may be a push for thinfilm, allsolidstate microbatteries, which will enable distributedpower sources in combination with their own charger and electrical appliance or load. An example of such integration mightbe an electrical device powered by a secondary battery connected to a photovoltaic charger.

Donald R. Sadoway

BibliographyClaus Daniel and J. O. Besenhard (eds.), Handbook of Battery Materials, WileyVCH, 2d ed., 2011

T. R. Crompton, Battery Reference Book, 3d ed., Newnes, 2000

R. A. Huggins, Advanced Batteries: Materials Science Aspects, Springer, 2008

KirkOthmer Encyclopedia of Chemical Technology, 5th ed., Wiley, 2007

T. Reddy, Linden's Handbook of Batteries, 4th ed., McGrawHill, 2010

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Additional ReadingsD. Andrea, Battery Management Systems for Large LithiumIon Battery Packs, Artech House, Norwood, MA, 2010

N. J. Giordano, Reasoning and Relationships, Brooks/Cole, Belmont, CA, 2010

J. W. Moore, C. L. Stanitski, and P. C. Jurs, Principles of Chemistry: The Molecular Science, Brooks/Cole, Belmont, CA,2010

C. D. Rahn and C. Wang, Battery Systems Engineering, John Wiley & Sons, Chichester, West Sussex, UK, 2013

S. Seki et al., Imidazoliumbased roomtemperature ionic liquid for lithium secondary batteries: Relationships betweenlithium salt concentration and battery performance characteristics, ECS Electrochem. Lett., 1(6):A77–A79, 2012 DOI:10.1149/2.003206eel (http://dx.doi.org/10.1149/2.003206eel)

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http://dx.doi.org/10.1149/2.003206eel

BatteryContent TypesComponentsSizeSelection and applicationsPrimary battery usageSecondary battery usage

RatingsLifePrimary BatteriesZinccarbon cellsMagnesium cellsAlkalinemanganese dioxide cellsMercuric oxide cellsSilver oxide cellsZincair cellsLithium cellsSolidelectrolyte cellsReserve batteriesZincsilver oxide reserve batteriesMagnesium wateractivated batteriesLithiumanode reserve batteriesThermal batteries

Secondary BatteriesLeadacid batteriesNickelcadmium batteriesNickelmetal hydride batteriesSilverzinc batteriesSodiumsulfur batteriesZincair batteriesLithiumion batteriesLithiumsolid polymer electrolyte (SPE) batteriesOutlook

BibliographyAdditional Readings

battery · zincair batteries lithiumion batteries lithiumsolid polymer electrolyte (spe) batteries...

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