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ULTRACAPACITOR SEMINARREPORT

INTRODUCTION

GeneralElectricengineersexperimentingwithdevicesusingporouscarbon

electrodesfirstobservedtheEDLCeffectin1957.[5]Theybelievedthattheenergy

was stored in the carbonpores and the device exhibited "exceptionally high

capacitance",althoughthemechanismwasunknownatthattime.GeneralElectric

didnotimmediatelyfollowuponthiswork.In1966researchersatStandardOilof

Ohio developed the modern version of the devices, after they accidentally re-

discoveredtheeffectwhileworkingonexperimentalfuelcelldesigns.[6]Theircell

designusedtwolayersofactivatedcharcoalseparatedbyathinporousinsulator,

andthisbasic mechanicaldesignremains thebasisofmostelectricdouble-layer

capacitors.StandardOilalsofailedtocommercializetheirinvention,licensingthe

technologytoNEC,whofinallymarketedtheresultsassupercapacitorsin1978,

to provide backup power for maintaining computer memory.[6] The market

expandedslowly

for

atime,

but

starting

around

the

mid-1990s

various

advances

in

materialsscienceandrefinementoftheexistingsystemsledtorapidlyimproving

performance and an equally rapid reduction in cost. The first trials of

supercapacitors in industrial applications were carried out for supporting the

energysupplytorobots.[7]In2005aerospacesystemsandcontrolscompanyDiehl

LuftfahrtElektronik GmbH chose supercapacitors topower emergency actuation

systemsfordoorsandevacuationslidesinairliners,includingthenewAirbus380

jumbojet.[8]In2005,theultracapacitormarketwasbetweenUS$272millionand

$400million,dependingonthesource.Asof2007allsolidstatemicrometer-scale

electricdouble-layercapacitorsbasedonadvancedsuperionicconductorshadbeen

for low-voltage electronics suchas deep-sub-voltage nanoelectronics and related

technologies(the22nmtechnologicalnodeofCMOSandbeyond).

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Theelectrochemicalultracapacitorisanemergingtechnologythatpromisestoplay

animportantroleinmeetingthedemandsofelectronicdevicesandsystemsboth

nowandinthefuture.Thisnewlyavailabletechnologyofultracapacitorsis

makingiteasierforengineerstobalancetheiruseofbothenergyandpower.

Energystoragedeviceslikeultracapacitorsarenormallyusedalongwithbatteries

tocompensateforthelimitedbatterypowercapability.Evidently,theproper

controloftheenergystoragesystemspresentsbothachallengeandopportunityfor

thepowerandenergymanagementsystem.Thispapertracesthehistoryofthe

developmentofthetechnologyandexplorestheprinciplesandtheoryofoperation

oftheultracapacitors. Theuseofultracapacitorsinvariousapplicationsare

discussedandtheiradvantagesoveralternativetechnologiesareconsidered.To

provideexampleswithwhichtooutlinepracticalimplementationissues,systems

incorporatingultracapacitorsasvitalcomponentsarealsoexplored.Thispaperhas

aimedtoprovideabriefoverviewofultracapacitortechnologyasitstandstoday.

Previousdevelopmenteffortshavebeendescribedtoplacethecurrentstateofthe

technologywithinanhistoricalcontext.Scientificbackgroundhasalsobeen

coveredinordertobetterunderstandperformancecharacteristics.

Possibleapplicationsofultracapacitortechnologyhavealsobeendescribedto

illustratethewiderangeofpossibilitiesthatexist.Becauseoftheadvantagesof

chargingefficiency,longlifetime,fastresponse,andwideoperatingtemperature

range,itistemptingtotryandapplyultracapacitorstoanyapplicationthatrequires

energystorage.Thelimitationsofthecurrenttechnologymustbefullyappreciated,

however,anditisimportanttorealizethatultracapacitorsareonlyusefulwithina

finiterangeofenergyandpowerrequirements.Outsideoftheseboundariesother

alternativesarelikelytobethebettersolution.Themostimportantthingto

rememberaboutultracapacitorstechnologyisthatitisanewanddifferent

technologyinitsownright.

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CONCEPT

Comparisonofconstructiondiagramsofthreecapacitors.Left:"normal"capacitor,

middle: electrolytic, right: electric double-layer capacitorIn a conventional

capacitor,energyisstoredbytheremovalofchargecarriers,typicallyelectrons,

from one metalplate and depositing them on another. This charge separation

createsapotentialbetweenthetwoplates,whichcanbeharnessedinanexternal

circuit.Thetotalenergystoredinthisfashionisproportionaltoboththeamountof

chargestoredandthepotentialbetweentheplates.Theamountofchargestored

perunitvoltageisessentiallyafunctionofthesize,thedistance,andthematerial

propertiesoftheplatesandthematerialinbetweentheplates(thedielectric),while

thepotentialbetween theplates is limitedbybreakdown of the dielectric. The

dielectriccontrolsthecapacitor'svoltage.

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Optimizing the material leads to higher energy density for a given size of

capacitor.EDLCsdonothaveaconventionaldielectric.Ratherthantwoseparate

platesseparatedbyaninterveningsubstance,thesecapacitorsuse"plates"thatare

infacttwolayersofthesamesubstrate,andtheirelectricalproperties,theso-called

"electrical double layer", result in the effective separation of charge despite the

vanishinglythin(ontheorderofnanometers)physicalseparationofthelayers.The

lackofneedforabulkylayerofdielectricpermitsthepackingofplateswithmuch

larger surface area into a given size, resulting in high capacitances inpractical-

sized packages.In an electrical double layer, each layer by itself is quite

conductive,but thephysics at the interface where the layers are effectively in

contact meansthatnosignificantcurrentcanflowbetweenthe layers.However,

the double layer can withstand only a low voltage, which means that electric

double-layercapacitorsratedforhighervoltagesmustbemadeofmatchedseries-

connected individual EDLCs, much like series-connected cells in higher-voltage

batteries.EDLCs have much higherpower density thanbatteries. Power density

combinestheenergydensitywiththespeedthattheenergycanbedeliveredtothe

load. Batteries, which arebased onthe movementofcharge carriers in a liquid

electrolyte, have relatively slow charge and discharge times. Capacitors, on the

other hand, canbe charged or discharged at a rate that is typically limitedby

currentheatingoftheelectrodes.SowhileexistingEDLCshaveenergydensitiesthat areperhaps 1/10 that of a conventionalbattery, theirpower density isgenerally10to100timesasgreat(seediagram,right).

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Thecapacitorthenevolvedintoanelectrostaticcapacitorwheretheelectrodes

weremadeupoffoilsandseparatedbypaperthatservedasthedielectric.These

capacitorsareusedintheelectroniccircuitboardsofanumberofconsumer

applications.Herethesurfaceareaofoneelectrodewasincreasedbyetchingthe

electrodetoroughenit,reducingthethicknessofthedielectricandusingapaste-

likeelectrolytetoformthesecondelectrode.

Anultracapacitorhoweverhasasignificantlylargerstoragearea.Ultracapacitors

aremadewithhighlyporouscarbonmaterials.Thesematerialshavethecapability

of

increased

surface

areas

ranging

greater

than

21,500

square

feet

per

gram.

The

separationdistancebetweenthechargedplatesisreducedsignificantlyto

nanometers(10(-9)cm)intheultracapacitorsbyusingelectrolytestoconductthe

chargedions.

Althoughtheyarecomparedtobatteriesfromtheapplicationperspective,

ultracapacitors areuniquebecausetherearenochemicalreactionsinvolved.They

areconsideredefficientastheycanquicklystoreandreleaseelectricalenergyin

thephysicalform.

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ULTRACAPACITOR

OperatingprinciplesoftheultracapacitorThecharge-storagemechanismandthedesignoftheultracapacitoraredescribed.

Basedonaceramicwithanextremelyhighspecificsurfaceareaandametallic

substrate,theultracapacitorprovidesextremelyhighenergydensityandexhibits

lowESR(equivalentseriesresistance).ThecombinationoflowESRand

extremelylowinductanceprovidestheultracapacitorwithaveryhighpower

densityandfastrisetimeaswell.Asadouble-layercapacitor,theultracapacitoris

notconstrainedbythesamelimitationsasdielectriccapacitors.Thus,althoughits

dischargecharacteristicsandequivalentcircuitaresimilartothoseofdielectric

capacitors,thecapacitanceoftheultracapacitorincreaseswiththeceramicloading

onthesubstrateanditsESRisinverselyproportionaltothecross-sectionalareaof

thedevice.Theultracapacitoriscomposedofaninlinestackofelectrodes,which

leadstoanextremelylowinductancedevice,anditexhibitsinterestingfrequency

dependence.Theultracapacitorprinciplehasbeenextendedtononaqueous

electrolytesandtoawidetemperaturerange.

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History

General Electricengineersexperimentingwithdevicesusingporouscarbon

electrodesfirstobservedtheEDLCeffectin1957.[5]Theybelievedthatthe

energy

wasstoredinthecarbonporesandthedeviceexhibited"exceptionallyhigh

capacitance",althoughthemechanismwasunknownatthattime.

GeneralElectricdidnotimmediatelyfollowuponthiswork.In1966researchers

atStandard Oil of Ohiodevelopedthemodernversionofthedevices,afterthey

accidentallyre-discoveredtheeffectwhileworkingonexperimentalfuel

celldesigns.[6]

Theircelldesignusedtwolayersofactivated charcoalseparatedby

athinporousinsulator,andthisbasicmechanicaldesignremainsthebasisofmost

electricdouble-layercapacitors.

StandardOildidnotcommercializetheirinvention,licensingthetechnology

toNEC,whofinallymarketedtheresultsassupercapacitorsin1978,toprovide

backuppowerformaintainingcomputermemory.[6]Themarketexpandedslowly

for

a

time,

but

starting

around

the

mid-1990s

various

advances

in

materials

scienceandrefinementoftheexistingsystemsledtorapidlyimproving

performanceandanequallyrapidreductionincost.

Thefirsttrialsofsupercapacitorsinindustrialapplicationswerecarriedoutfor

supportingtheenergysupplytorobots.[7]

In2005aerospacesystemsandcontrolscompanyDiehl LuftfahrtElektronikGmbH

chosesupercapacitorstopoweremergencyactuationsystemsfordoors

andevacuation slidesinairliners,includingthenewAirbus 380jumbojet.[8]In

2005,theultracapacitormarketwasbetweenUS$272millionand$400million,

dependingonthesource.

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MATERIALS

Ingeneral,EDLCsimprovestoragedensitythroughtheuseofananoporous

material, typically activated charcoal, inplace of the conventional insulating

barrier. Activated charcoal is apowder made up of extremely small and very

"rough"particles,which, inbulk, forma low-densityheapwith manyholesthat

resemblesasponge.Theoverallsurfaceareaofevenathinlayerofsuchamaterial

is many times greater than a traditional material like aluminum, allowing many

more charge carriers (ions or radicals from the electrolyte) tobe stored in any

givenvolume.Thecharcoal,whichisnotagoodinsulator,replacestheexcellent

insulators used in conventionaldevices, so in generalEDLCs can only use low

potentialsontheorderof2to3V.

Activated charcoal is not the "perfect" material for this application. The charge

carriers are actually (in effect) quite largeespecially when surrounded by

solventmoleculesandareoftenlargerthantheholesleftinthecharcoal,which

aretoosmalltoacceptthem,limitingthestorage.

Asof2010virtuallyallcommercialsupercapacitorsusepowderedactivatedcarbon

madefromcoconutshells.[citationneeded][11]Higherperformancedevicesareavailable,at a significant cost increase,based on synthetic carbonprecursors that are

activatedwithpotassiumhydroxide(KOH).[11]

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ResearchinEDLCsfocusesonimprovedmaterialsthatofferhigherusablesurfaceareas.

Graphene has excellent surface areaper unit of gravimetric or volumetric

densities,ishighlyconductiveandcannowbeproducedinvariouslabs,but

is not available inproduction quantities. Specific energy density of 85.6

Wh/kgatroomtemperatureand136Wh/kgat80C(allbasedonthetotal

electrode weight), measured at a current density of 1 A/g havebeen

observed.TheseenergydensityvaluesarecomparabletothatoftheNickel

metalhydridebattery.

Thedevicemakesfullutilizationofthehighestintrinsicsurfacecapacitance

and specific surface area of single-layer graphenebypreparing curved

graphenesheetsthatdonotrestackface-to-face.Thecurvedshapeenables

the formationofmesoporesaccessibleto andwettablebyenvironmentally

benignionicliquidscapableofoperatingatavoltage>4V.[12]

Carbon nanotubes have excellent nanoporosityproperties, allowing tiny

spaces forthepolymer to sit in the tube and actas a dielectric.[13]Carbon

nanotubescanstoreaboutthesamechargeascharcoal(whichisalmostpure

carbon)per unit surface areabut nanotubes canbe arranged in a more

regularpatternthatexposesgreatersuitablesurfacearea.[14]

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Ragonechartshowingenergydensityvs.powerdensityforvariousenergy-storage

devices

Somepolymers (e.g.polyacenes and conductingpolymers) have a redox

(reduction-oxidation)storagemechanismalongwithahighsurfacearea.

Carbonaerogelprovidesextremelyhighsurfaceareagravimetricdensitiesof

about4001000m/g.

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Theelectrodesofaerogelsupercapacitorsareacompositematerialusually

madeofnon-wovenpapermadefromcarbonfibersandcoatedwithorganic

aerogel, which then undergoes pyrolysis. The carbon fibers provide

structuralintegrityandtheaerogelprovidestherequiredlargesurfacearea.

Smallaerogelsupercapacitors arebeingusedasbackupelectricitystoragein

microelectronics.

Aerogelcapacitorscanonlyworkatafewvolts;highervoltagesionizethe

carbonanddamagethecapacitor.Carbonaerogelcapacitorshaveachieved

325J/g(90Wh/kg)energydensityand20W/gpowerdensity.[15]

Solidactivatedcarbon,alsotermedconsolidatedamorphouscarbon(CAC).It can have a surface area exceeding 2800 m2/g and maybe cheaper to

producethanaerogelcarbon.[16]

Tunable nanoporous carbon exhibits systematic pore size control.

H2adsorption treatment canbe used to increase the energy densityby as

muchas75%overwhatwascommerciallyavailableasof2005.[17][18]

Mineral-based carbon is a nonactivated carbon, synthesised frommetalor

metalloidcarbides,e.g.SiC,TiC,Al4C3.[19]Thesynthesisednanostructured

porouscarbon,oftencalledCarbideDerivedCarbon(CDC), hasasurface

areaofabout400m/gto2000m/gwithaspecificcapacitanceofupto100

F/mL(inorganicelectrolyte).

Asof2006thismaterialwasusedinasupercapacitorwithavolumeof135

mLand200gweighthaving1.6kFcapacitance.Theenergydensityismore

than47kJ/Lat2.85Vandpowerdensityofover20W/g.[20]

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In August 2007 researchers combined abiodegradablepaperbattery with

alignedcarbonnanotubes,designedtofunctionasbothalithium-ionbattery

andasupercapacitor(calledbacitor).Thedeviceemployedanionicliquid,essentiallya liquidsalt,astheelectrolyte.Thepapersheetscanberolled,

twisted,folded,orcutwithnolossofintegrityorefficiency,orstacked,like

ordinarypaper(oravoltaicpile),toboosttotaloutput.

Theycanbemadeinavarietyofsizes,frompostagestamptobroadsheet.

Their light weight and low cost make them attractive for portable

electronics, aircraft, automobiles, and toys (such as modelaircraft), while

their ability to use electrolytes inblood make thempotentially useful for

medicaldevicessuchaspacemakers.[21]

Other teams are experimenting with custom materials made of activated

polypyrrole,andnanotube-impregnated papers.

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DENSITY

TheenergydensityofexistingcommercialEDLCsrangesfromaround0.5to30

Wh/kg[22][23]includinglithiumioncapacitors,knownalsoasa"hybridcapacitor".

Experimental electric double-layer capacitors have demonstrated densities of 30

Wh/kg and havebeen shown tobe scalable to at least 136 Wh/kg,[24][25] while

othersexpecttoofferenergydensitiesofabout400Wh/kg.[26]Forcomparison,a

conventional lead-acidbattery stores typically 30 to 40 Wh/kg and modern

lithium-ionbatteriesabout160Wh/kg.Gasolinehasanetcalorificvalue(NCV)

ofaround12,000Wh/kg;automobileapplicationsoperateatabout20%tank-to-

wheelefficiency,givinganeffectiveenergydensityof2,400Wh/kg.

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ENERGYSTORAGE: Inthepast2classeswehavediscussedbatterytechnologiesandhowtheir

characteristicsmayormaynotbesuitableformicrogrids.

Batteriesaresuitableforapplicationswhereweneedanenergydeliveryprofile.

Forexample,tofeedaloadduringthenightwhentheonlysourceisPVmodules.

However,batteriesarenotsuitableforapplicationswithpowerdeliveryprofiles.

Forexample,toassistaslowload-followingfuelcellindeliveringpowertoa

constantlyandfastchangingload.

Forthislastapplication,twotechnologiesseemtobemoreappropriate:

Ultracapacitors(electricenergy)

Flywheels(mechanicalenergy)

Otherenergystoragetechnologiesnotdiscussedinherearesuperconducting

magneticenergystorage(SMESmagneticenergy)andcompressedair(orsome

othergas-mechanicalenergy)

FLYWHEEL:

Kineticenergy:

whereIisthemomentofinertiaand istheangularvelocityofarotatingdisc.

Foracylinderthemomentofinertiais

Sotheenergyisincreasedif increasesorifIincreases.

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Icanbeincreasedbylocatingasmuchmassontheoutsideofthediscas

possible.

Butasthespeedincreasesandmoremassislocatedoutsideofthedisc,

mechanicallimitationsaremoreimportant.

However,highspeedisnottheonlymechanicalconstraint

Ifinsteadofholdingoutputvoltageconstant,outputpowerisheldconstant,then

thetorqueneedstoincrease(becauseP=T )asthespeeddecreases.Hence,there

isalsoaminimumspeedatwhichnomorepowercanbeextracted

Ifandifanusefulenergy(Eu)proportionaltothedifferencebetweenthedisk

energyatitsmaximumandminimumallowedspeediscomparedwiththe

maximumallowedenergy.

CHARECTERSTIC:

Thesignificantcharacteristicsofultracapacitorsare:

Lowinternalresistanceincomparisonwithbatteries

Highpowerdensityduetohighdischargecurrents

Abilitytooperateattemperaturesaslowas-40C

Effectivecapacitanceforspecificpulsewidths

Lowequivalentseriesresistance(ESR)

Highercyclelife,makingthemsuitableforautomotiveapplications

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ADVANTAGES

Longlife,withlittledegradationoverhundredsofthousandsofcharge

cycles.Duetothecapacitor'shighnumberofcharge-dischargecycles

(millionsormorecomparedto200to1000formostcommerciallyavailable

rechargeablebatteries)itwilllastfortheentirelifetimeofmostdevices,

whichmakesthedeviceenvironmentallyfriendly.Rechargeablebatteries

wearouttypicallyoverafewyears,andtheirhighlyreactivechemical

electrolytespresentadisposalandsafetyhazard.Batterylifetimecanbe

optimisedbychargingonlyunderfavorableconditions,atanidealrateand,

forsomechemistries,asinfrequentlyaspossible.EDLCscanhelpin

conjunctionwithbatteriesbyactingasachargeconditioner,storingenergy

fromothersourcesforloadbalancingpurposesandthenusinganyexcess

energytochargethebatteriesatasuitabletime.

Lowcostpercycle Goodreversibility

Veryhighratesofchargeanddischarge.

Extremelylowinternalresistance(ESR)andconsequenthighcycle

efficiency(95%ormore)andextremelylowheatinglevels

Highoutputpower

Highspecific

power.

According

toITS

(Institute

ofTransportation

Studies,

Davis,California)testresults,thespecificpowerofelectricdouble-layer

capacitorscanexceed6kW/kgat95%efficiency[10]

Improvedsafety,nocorrosiveelectrolyteandlowtoxicityofmaterials.

.

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DISADVANTAGES

Theamountofenergystoredperunitweightisgenerallylowerthanthatof

anelectrochemicalbattery(35Wh/kgforanstandardultracapacitor,

although85W.h/kghasbeenachievedinthelab[3]asof2010comparedto

30-40Wh/kgforaleadacidbattery),andabout1/1,000ththevolumetric

energydensityofgasoline.

Typicalofanycapacitor,thevoltagevarieswiththeenergystored.Effective

storageandrecoveryofenergyrequirescomplexelectroniccontroland

switchingequipment,withconsequentenergyloss

Hasthehighestdielectricabsorptionofanytypeofcapacitor.

Highself-discharge-therateisconsiderablyhigherthanthatofan

electrochemicalbattery.

Cellsholdlowvoltages-serialconnectionsareneededtoobtainhigher

voltages.Voltagebalancingisrequiredifmorethanthreecapacitorsare

connectedinseries.

Lineardischargevoltagepreventsuseofthefullenergyspectrum.

Duetorapidandlargereleaseofenergy(albeitovershorttimes),EDLC's

havethepotentialtobedeadlytohumans.

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APPLICATIONS

Someoftheearliestusesweremotorstartupcapacitorsforlargeenginesintanks

and submarines, and as the costhas fallenthey have started to appearondiesel

trucks and railroad locomotives.[27][28] In the 00's they attracted attention in the

greenenergyworld,wheretheirabilitytochargemuchfasterthanbatteriesmakes

themparticularlysuitableforregenerativebrakingapplications.Newtechnologyin

developmentcouldpotentiallymakeEDLCswithhighenoughenergydensitytobe

anattractive replacement forbatteries in all-electric cars andplug-in hybrids, as

EDLCschargequicklyandarestablewithrespecttotemperature.

Chinaisexperimentingwithanewformofelectricbus(capabus)thatrunswithout

powerlinesusinglargeonboardEDLCs,whichquicklyrechargewheneverthebus

is at anybus stop (under so-called electric umbrellas), and fully charge in theterminus.AfewprototypeswerebeingtestedinShanghaiinearly2005.In2006,

twocommercialbusroutesbegantouseelectricdouble-layercapacitorbuses;one

ofthemisroute11inShanghai.[29]

In 2001 and 2002 VAG, thepublic transport operator inNuremberg, Germany

testedanhybridbusthatusesadiesel-electricbatterydrivesystemwithelectric

double-layer capacitors.[30] Since 2003 Mannheim Stadtbahn in Mannheim,

Germanyhasoperatedalight-railvehicle(LRV)thatusesEDLCstostorebraking

energy.[31][32]

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OtherpublictransportmanufacturersaredevelopingEDLCtechnology,including

mobilestorage[33]andastationarytracksidepowersupply.[34][35]

Atriplehybridforklifttruckusesfuelcellsandbatteriesasprimaryenergystorage

Automotive

Ultracapacitors are used in some conceptprototype vehicles, in order to keep

batteries within resistive heating limits and extend battery life.[37][38] The

ultrabattery combines a supercapacitor and abattery in one unit, creating an

electric vehiclebattery that lasts longer, costs less and is morepowerful than

currentplug-inhybridelectricvehicles(PHEVs).[39][40]

Motor racing

The FIA, the governingbody for many motor racing events,proposed in the

Power-TrainRegulationFrameworkforFormula1 version1.3of23May2007thatanewsetofpowertrainregulationsbeissuedthatincludesahybriddriveof

up to 200kW input and outputpower using "superbatteries" made withboth

batteriesandsupercapacitors. [41]

Consumer electronics

EDLCs canbe used in PC Cards, flashphotography devices in digitalcameras,

flashlights,portablemediaplayers,andinautomatedmeterreading,[42]particularly

whereextremelyfastchargingisdesirable.

In2007,acordlesselectricscrewdriverthatusesanEDLCforenergystoragewas

produced.[43]Itchargesin90seconds,retains85%ofthechargeafter3 months,

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andholdsenoughchargeforabouthalfthescrews(22)acomparablescrewdriver

witharechargeablebatterywillhandle(37).Two LED flashlightsusingEDLCs

werereleasedin2009.Theychargein90seconds.[44]

Alternative energy

The idea ofreplacingbatterieswithcapacitors inconjunctio

nwith novelenergy

sourcesbecame a conceptualumbrella of the Green Electricity(GEL)Initiative,

introducedbyDr.AlexanderBell.[45]OnesuccessfulGELInitiativeconceptwasa

muscle-driven autonomous solution that employs a multi-farad EDLC as energy

storagetopoweravarietyofportableelectricalandelectronicdevicessuchasMP3

players,AM/FMradios,flashlights,cellphones,andemergencykits.[46]

Price

Costs have fallen quickly, with costper kilojoule dropping faster than costper

farad.Asof2006thecostofsupercapacitorswas1centperfaradand$2.85per

kilojoule,andwasexpectedtodropfurther.[47]

Market

According to Innovative Research and Products (iRAP), ultracapacitor market

growth will continue during 2009 to 2014. Worldwidebusiness, over US$275

millionin2009,willcontinuetogrowatanAAGRof21.4%through2014.[48]

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Challenges:

1.Theforemostchallengeisfromtraditionalbatteriessuchas

theleadacid,lithium

ion,nickelcadmium(NiCD),nickelmetalhydride(NiMH)andotherswhich

existedinthemarketformorethanhundredyears

2.EquivalentSeriesResistancevaluescanbeoptimizedonlywithefficient

packagingoftheultracapacitor

3.Costofrawmaterialsaresignificantlyhighandplaysanimportantroleinthe

pricingofultracapacitors

4.Adoptionratesareonlygraduallyincreasingasend-usersrealizethebenefitsof

ultracapacitors

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CONCLUSION

Ultracapacitorshavemanyadvantagesovertraditionalelectrochemicalbatteries.

Unlikebatteries,"ultracaps"cancompletelyabsorbandreleaseachargeathigh

ratesandinavirtuallyendlesscyclewithlittledegradation.Wherethey'reweak,

however, is with energy storage. Compared with lithium-ionbatteries, high-end

ultracapacitors onthe markettodaystore 25times lessenergyperpound.This is

whyultracapacitors,withtheirabilityto releasequickjoltsofelectricityandto

absorbthisenergyjustasfast,areidealtodayasacomplementtobatteriesorfuel

cellsinelectric-drivevehicles.Thepowerburstthatultracapsprovidecanassist

withstop-startacceleration,andtheenergyismoreefficientlyrecapturedthrough

regenerativebraking--anareainwhichultracapmakerMaxwellTechnologieshas

seensignificantresults.Infutureitwillreplacethebatteries.

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REFERENCE

www.Pediain.com

SuperCapacitorSeminar

Articleonultracapacitorsatelectronicdesign.com

Articleonultracapacitorsatbatteryuniversity.com

Anewversionofanoldideaisthreateningthebatteryindustry(The

Economist).

AnEncyclopediaArticleFromtheYeagercenteratCWRU.


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