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wikiSupercapacitors2

Supercapacitor

MaxwellTechnologies"MC"and"BC"seriessupercapacitors（upto3000faradcapacitance）

Supercapacitors（SC）,[1]compriseafamilyofelectrochemicalcapacitors.Supercapacitors,sometimescalledultracapacitorsorelectricdouble-layercapacitor（EDLC）,don'thaveaconventionalsoliddielectric.Thecapacitancevalueofanelectrochemicalcapacitorisdeterminedbytwostorageprinciples,bothofwhichcontributetothetotalcapacitanceofthecapacitor:

[2][3][4]

∙Double-layercapacitance–electrostaticstorageoftheelectricalenergyachievedbyseparationofchargeinaHelmholtzdoublelayerattheinterfacebetweenthesurfaceofaconductiveelectrodeandanelectrolyte.Thedistanceofthestaticseparationofchargeinadouble-layerisontheorderofafewAngstroms（0.3–0.8 nm）whichisextremelysmall.[5]

∙Pseudocapacitance–Electrochemicalstorageoftheelectricalenergywithelectrontransfer,achievedbyredoxreactionswithspecificallyadsorbedionsfromtheelectrolyte,intercalationofatomsinthelayerlatticeorelectrosorption,underpotentialdepositionofhydrogenormetaladatomsinsurfacelatticesiteswhichresultinareversiblefaradaiccharge-transfer.[5]

Theratioofthestorageresultingfromeachprinciplecanvarygreatly,dependingonelectrodedesignandelectrolytecomposition.Pseudocapacitancecanincreasethecapacitancevaluebyasmuchasanorderofmagnitudeoverthatofthedouble-layerbyitself.[1]

Supercapacitorsaredividedintothreefamilies,basedonthedesignoftheelectrodes:

∙Double-layercapacitors–withcarbonelectrodesorderivateswithmuchhigherstaticdouble-layercapacitancethanthefaradaicpseudocapacitance

∙Pseudocapacitors–withelectrodesoutofmetaloxidesorconductingpolymerswithahighamountoffaradaicpseudocapacitance

∙Hybridcapacitors–capacitorswithspecialandasymmetricelectrodesthatexhibitbothsignificantdouble-layercapacitanceandpseudocapacitance,suchaslithium-ioncapacitors

Hierarchicalclassificationofsupercapacitorsandrelatedtypes

Supercapacitorsbridgethegapbetweenconventionalcapacitorsandrechargeablebatteries.Theyhavethehighestavailablecapacitancevaluesperunitvolumeandthegreatestenergydensityofallcapacitors.Theysupportupto12,000Farads/1.2Volt,[6]withcapacitancevaluesupto10,000timesthatofelectrolyticcapacitors.[1]Whileexistingsupercapacitorshaveenergydensitiesthatareapproximately10%ofaconventionalbattery,theirpowerdensityisgenerally10to100timesgreater.Powerdensityisdefinedastheproductofenergydensity,multipliedbythespeedatwhichtheenergyisdeliveredtotheload.Thegreaterpowerdensityresultsinmuchshortercharge/dischargecyclesthanabatteryiscapable,andagreatertolerancefornumerouscharge/dischargecycles.

Withinelectrochemicalcapacitors,theelectrolyteistheconductiveconnectionbetweenthetwoelectrodes,distinguishingthemfromelectrolyticcapacitors,inwhichtheelectrolyteonlyformsthecathode,thesecondelectrode.

Supercapacitorsarepolarizedandmustoperatewithcorrectpolarity.Polarityiscontrolledbydesignwithasymmetricelectrodes,or,forsymmetricelectrodes,byapotentialappliedduringthemanufacturingprocess.

Supercapacitorssupportabroadspectrumofapplicationsforpowerandenergyrequirements,including:

∙Lowsupplycurrentduringlongertimesformemorybackupin（SRAMs）

∙Powerelectronicsthatrequireveryshort,highcurrent,asintheKERSsysteminFormula1cars

∙Recoveryofbrakingenergyforvehicles

Exceptionalforelectroniccomponentslikecapacitorsarethemanifolddifferenttradeorseriesnamesusedforsupercapacitorslike:

APowerCap,BestCap,BoostCap,CAP-XX,DLCAP,EneCapTen,EVerCAP,DynaCap,Faradcap,GreenCap,Goldcap,HY-CAP,Kaptoncapacitor,Supercapacitor,SuperCap,PASCapacitor,PowerStor,PseudoCap,Ultracapacitormakingitdifficultforuserstoclassifythesecapacitors.

Contents

∙1History

o1.1Developmentofthedoublelayerandpseudocapacitancemodel

o1.2Developmentofelectrochemicalcapacitors

∙2Storageprinciples

o2.1Conventionalelectrostaticvselectrochemicalenergystorage

o2.2Electrostaticdouble-layercapacitance

o2.3Electrochemicalpseudocapacitance

∙3Typesofsupercapacitors

∙4Construction

∙5Materials

o5.1Electrodes

o5.2ElectrodesforEDLCs

o5.3Electrodesforpseudocapacitors

o5.4Electrodesforhybridcapacitors

o5.5Electrolytes

o5.6Separators

o5.7Collectorsandhousing

∙6Electricalparameters

o6.1Capacitance

o6.2Operatingvoltage

o6.3Internalresistance

o6.4Currentload

o6.5Cyclestability

o6.6Energydensityandpowerdensity

o6.7Lifetime

o6.8Self-discharge

o6.9Polarity

∙7Comparisationoftechnicalparameters

o7.1Comparisationofsupercapacitorparameters

o7.2Parametriccomparisonoftechnologies

∙8Standards

∙9Applications

o9.1Generalapplications

o9.2Heavyandpublictransport

∙10Newdevelopments

∙11Market

∙12Seealso

∙13Literature

∙14References

∙15Externallinks

History

Developmentofthedoublelayerandpseudocapacitancemodel

Helmholtz

Whenametal（oranelectronicconductor）isbroughtincontactwithasolidorliquidionic-conductor（electrolyte）,acommonboundary（interface）amongthetwodifferentphasesoriginates.Helmholtz[7]wasthefirsttorealizethatchargedelectrodesimmersedinelectrolyticsolutionsrepelthecoionsofthechargewhileattractingcounterionstotheirsurfaces.Withthetwolayersofoppositepolarityformedattheinterfacebetweenelectrodeandelectrolytein1853heshowedthatanelectricaldoublelayer（DL）thatisessentiallyamoleculeardielectricachievedelectrostaticchargestorage.[8]Belowtheelectrolyte'sdecompositionvoltagethestoredchargeislinearlydependentonthevoltageapplied.

ThisearlyHelmholtzmodelpredictedaconstantdifferentialcapacitanceindependentfromthechargedensitydependingonthedielectricconstantofthesolventandthethicknessofthedouble-layer.[5][9][10]Butthismodel,whileagoodfoundationforthedescriptionoftheinterface,doesnotconsiderimportantfactorsincludingdiffusion/mixingofionsinsolution,thepossibilityofadsorptionontothesurfaceandtheinteractionbetweensolventdipolemomentsandtheelectrode.

SimplifiedillustrationofthepotentialdevelopmentintheareaandinthefurthercourseofaHelmholtzdoublelayer.

Gouy\Chapman

LouisGeorgesGouyin1910andDavidLeonardChapmanin1913bothobservedthatcapacitancewasnotaconstantandthatitdependedontheappliedpotentialandtheionicconcentration.The“Gouy-Chapmanmodel”madesignificantimprovementsbyintroducingadiffusemodeloftheDL.InthismodelthechargedistributionofionsasafunctionofdistancefromthemetalsurfaceallowsMaxwell–Boltzmannstatisticstobeapplied.Thustheelectricpotentialdecreasesexponentiallyawayfromthesurfaceofthefluidbulk.[5][11]

Stern

Gouy-ChapmanmodelfailsforhighlychargedDLs.InordertoresolvethisproblemOttoSternin1924suggestedthecombinationoftheHelmholtzandGouy-Chapmanmodels.InStern'smodel,someoftheionsadheretotheelectrodeassuggestedbyHelmholtz,givinganinternalSternlayerandsomeformaGouy-Chapmandiffuselayer.[12]

TheSternlayeraccountedforions'finitesizeandconsequentlyionshaveaclosestapproachtotheelectrodeontheorderoftheionicradius.TheSternmodeltoohadlimitations,effectivelymodelingionsaspointcharges,assumingallsignificantinteractionsinthediffuselayerareCoulombic,assumingdielectricpermittivitytobeconstantthroughoutthedoublelayer,andthatfluidviscosityisconstantabovetheslippingplane.[13]

Grahame

Thus,D.C.GrahamemodifiedSternin1947.[14]HeproposedthatsomeionicorunchargedspeciescanpenetratetheSternlayer,althoughtheclosestapproachtotheelectrodeisnormallyoccupiedbysolventmolecules.Thiscouldoccurifionslosttheirsolvationshellwhentheionapproachedtheelectrode.Ionsindirectcontactwiththeelectrodewerecalled“specificallyadsorbedions”.Thismodelproposedtheexistenceofthreeregions.TheinnerHelmholtzplane（IHP）planepassingthroughthecentresofthespecificallyadsorbedions.TheouterHelmholtzplane（OHP）passesthroughthecentresofsolvatedionsattheirdistanceofclosestapproachtotheelectrode.FinallythediffuselayeristheregionbeyondtheOHP.

Schematicrepresentationofadoublelayeronanelectrode（BMD）model.1.InnerHelmholtzplane,（IHP）,2.OuterHelmholtzplane（OHP）,3.Diffuselayer,4.Solvatedions（cations）5.Specificallyadsorbedions（redoxion,whichcontributestothepseudocapacitance）,6.Moleculesoftheelectrolytesolvent

Bockris/Devanthan/Müller

In1963J.O'M.Bockris,M.A.VDevanthan,andK.AlexMüller[15]proposedamodel（BDMmodel）ofthedouble-layerthatincludedtheactionofthesolventintheinterface.Theysuggestedthattheattachedmoleculesofthesolvent,suchaswater,wouldhaveafixedalignmenttotheelectrodesurface.Thisfirstlayerofsolventmoleculesdisplayastrongorientationtotheelectricfielddependingonthecharge.Thisorientationhasgreatinfluenceonthepermittivityofthesolventwhichvarieswiththefieldstrength.TheinnerHelmholtzplane（IHP）passesthroughthecentersofthesemolecules.Specificallyadsorbed,partiallysolvatedionsappearinthislayer.ThesolvatedionsoftheelectrolyteareoutsidetheIHP.Throughthecentersoftheseionspassasecondplane,theouterHelmholtzplane（OHP）.TheregionbeyondtheOHPiscalledthediffuselayer.TheBDMmodelnowismo