电化学电容器介绍

电化学电容器及其电极材料的进展介绍报告人：王宇学号：BA13014006Whatiscapacitors?Whatiselectrochemicalcapacitors(supercapacitors)?电容器（Capacitor）是两金属板之间存在绝缘介质的一种电路元件。其单位为法拉，符号为F。电容器利用二个导体之间的电场来储存能量，二导体所带的电荷大小相等，但符号相反。当电性相反的电荷分别在电容器的两端累积，电容器两端的电位差和电荷产生的电场开始增加。累积电荷越多，为抵抗电场所需要作的功就越大。储存在电容器的能量（国际单位制中，单位为焦耳）等于建立电容两端的电压和电场所需要的能量。电化学电容器（supercapacitor）与上述电容器不同的地方是：两金属板之间存在绝缘介质变成了浸没在电解液中具有电化学活性的材料。基本原理相同，都是在电极处累积电荷达到能量存储的目的。Quetal.JournalofPowerSources,74(1998)99–107油相与水相E=½CV2Aqueouselectrolytes,suchasacids(e.g.,H2SO4)andalkalis(e.g.,KOH)havetheadvantageofhighionicconductivity(upto∼1

S

cm−1),lowcostandwideacceptance.Ontheotherhand,theyhavetheinherentdisadvantageofarestrictedvoltagerangewitharelativelylowpositionvoltageof∼1.23

V.Non-aqueouselectrolytesofvarioustypeshavebeendevelopedthatallowtheuseofcelloperatingvoltages∼2.5

V.Non-aqueouselectrolytemixturessuchaspropylenecarbonateoracetonitrile,containingdissolvedquaternaryalkylammoniumsalts,havebeenemployedinmanycommercialsupercapacitors,particularlythosetargetinghigherenergyapplications.Theelectricalresistivityofnon-ueouselectrolytesis,however,atleastanorderofmagnitudehigherthanthatofaqueouselectrolytesandthereforetheresultingcapacitorsgenerallyhaveahigherinternalresistance.NatureMater.7,845-854(2008)Ifasupercapacitorisusedinanelectricvehicle,thespecificpowershowshowfastonecango,andthespecificenergyshowshowfaronecangoonasinglecharge.Timesshownarethetimeconstantsofthedevices,obtainedbydividingtheenergydensitybythepower.Electrochemicalcapacitorscurrentlyfillthegapbetweenbatteriesandconventionalsolidstateandelectrolyticcapacitors.能量比较图特点Batteries:HighenergydensityandlowpowerdensityenergystoragesystemsElectrochemicalcapacitors:HighpowerdensityandlowenergydensitySolarenergyWind

energyWaterenergy……Advantagesof

Electrochemicalcapacitors(EC):HighpowerdensityLonglifeexpectancyLongshelflifeWiderangeofoperatingtemperatures

(downto-40°C).

EnvironmentalfriendlinessSafetyChallengesfor

EC：

LowenergydensityHighself-dischargingrateThefirstpatentdescribingtheconceptofanECwasfiledin1957byBecker.However,notuntilthe1990sdidECtechnologybegintodrawsomeattention,inthefieldofhybridelectricvehicles.Example1)toimprovetheoverallefficiencyofthevehicle2)toreducelong-termcostsbyextendingthelifeofthebatteries3)toimprovetheaccelerationcapabilitiesofthevehicle4)toreduceshort-termcostsbyreplacingsomeofthebatteries.IEEETransactionsonIndustryApplications,44,108-114(2008)InternationalSymposiumonPowerElectronics,ElectricalDrives,AutomationandMotion,727-732(2008)Theadditionofsupercapacitorscanplishoneormoreofthefollowinggoals:EC的分类：1.Electrostaticsupercapacitors2.FaradaicsupercapacitorsElectrochemicaldouble-layercapacitors(EDLCs)areelectrochemicalcapacitorsthatstorethechargeelectrostaticallyusingreversibleadsorptionofionsoftheelectrolyteontoactivematerialsthatareelectrochemicallystableandhavehighaccessibleSSA.SomeECsusefast,reversibleredoxreactionsatthesurfaceofactivematerials,thusdefiningwhatiscalledthepseudo-capacitivebehaviour.大多是碳材料大多是金属氧化物以及导电聚合物InternationalJournalofHydrogenEnergy.34,4889-4899(2009)Principleofasingle-celldouble-layercapacitorandillustrationofthepotentialdropattheelectrode/electrolyteinterface.Electrochemicaldouble-layercapacitors(EDLCs)Carbonmaterialsareconsideredprospective

electrode

materialsforindustrialization.highconductivity,highsurface-arearange(∼1to>2000

m2

g−1),goodcorrosionresistance,hightemperaturestability,controlledporestructure,processabilityandcompatibilityincompositematerials,relativelylowcost.ElectrodematerialcharacteristicsforEDLC

Highsurfaceareaactivematerialsa,SEMimageofSWNT-foreststructuralcollapsefromasingledropofliquid.

b,Schematicdiagramofthecollapseofthealignedlow-densityas-grownforest(above)tothehighlydenselypackedSWNTsolid(below).

c,Overlaidpicturesillustratingthedecreaseinlateraldimensionsbefore(grey)andafter(black)collapse.Thedouble-endedarrowindicatesthetubealignmentdirection.Scalebar,1

cm.

d,Ramanspectraforas-grownforest(blue)andSWNTsolid(red).e,

f,SEMimagesoftheas-grownforest(e)andsolid(f).

g,Atomicforcemicroscopeimageofsolidsurface.Brunauer–Emmett–Teller(BET)surfaceareaforthesolid,asdeterminedfromnitrogenadsorptionisothermswas1,000

m2

g-1,almostthesamewithforest.Forforests,thetypicalmassdensitywas0.03

g

cm-3;Forsolid,0.55

g

cm-3NatureMaterials

5,987-994(2006)a,b,CyclicvoltammogramsoftheEDLCusingtheSWNTsolidsheet(red)andas-grownforest(black)aselectrodescomparingthecapacitanceperweight(a)andcapacitancepervolume(b).

c,ChangeinthecapacitancepervolumeusingtheSWNTsolidsheet(red)andas-grownforest(black).

d,SchematicmodelcomparingtheiondiffusionforactivatedcarbonandtheSWNTsolidmaterial.

e,CapacitanceversusdischargecurrentdensitycomparingSWNTsolid(red)andactivatedcarbon(blue)for0.1and0.5

mmelectrodethicknesses(dashedandsolidlines,respectively).

f,Potentialdropassociatedwithanincreaseininternalresistance(IRdrop)forSWNTsolid(red)andactivatedcarbon(blue)for0.1and0.5

mmelectrodethicknesses(dashedandsolidlines,respectively).CapacitanceoftheSWNTsolidEDLCwasestimatedas20

F

g-1

fromthedischargecurvesofcellschargedat2.5

Vforatwo-electrodecell,andcorrespondsto80

F

g-1

forathree-electrodecell.Withtetraethylammoniumtetrafluoroborate(Et4NBF4)/propylenecarbonateelectrolyte.Zhu

etal.,Science

332,

1537-1541(2008)GraphenehasatheoreticalSSAof2630m2/gActivationwithKOHofmicrowaveexfoliatedGO(MEGO)toachieveSSAvaluesupto3100m2/g.BMIMBF4/ANaselectrolyte.Usingthespecificcapacitancevalueof166F/g(fromthedischargecurvewithaconstantcurrentof5.7A/g)andworkingvoltageof3.5V,theenergydensityis~70Wh/kgforthea-MEGOinthecell.

Redox-basedelectrochemicalcapacitorsCathodematerials：withtheaverageworkingpotentialofabove0Vvs.SCEAnodematerials：withtheaverageworkingpotentialofbelow0Vvs.SCE.Qu

etal.,Adv.Mater.

23,

5574-5580(2011)Qu

etal.,Adv.Mater.

23,

5574-5580(2011)Hydrousrutheniumoxide(RuO2·xH2O)NTswereelectrodepositedontoAAO-coatedgraphite(10×10×3mm)orTisubstrates(10×10×0.5mm)Itcanbedescribedasafast,reversibleelectrontransfertogetherwithanelectro-adsorptionofprotonsonthesurfaceofRuO2NTs,accordingtoequation,whereRuoxidationstatescanchangefrom(ii)upto(iv):where0≤x≤2.RuO2NTsforSupercapacitorsTherectangle-likeshapeofalli−Ecurvesmeasuredatvariousscanratesin1.0MH2SO4

(Figure4A)fortheannealedRuO2·xH2ONTsrevealstheperfectelectrochemicalreversibilityoftheFaradaicredoxtransitionsontheseoxideNTs.Figure4(A)Cyclicvoltammogramsmeasuredat(1)1000,(2)750,(3)500,(4)250,and(5)100mVs-1,and(B)dependenceofthecapacitancelossonthescanrateofCVfrom10to1000mVs-1

foranannealedRuO2·xH2ONTarrayedelectrode(0.19±0.01mgcm-2).(C)Electrochemicalimpedancespectrameasuredatvariouspotentialswithpotentialamplitudeof10mV.(D)FrequencydependenceofspecificcapacitanceforanannealedRuO2·xH2ONTarrayedelectrode(0.21±0.01mgcm-2).Theelectrolyteforelectrochemicalanalysesis1.0MH2SO4.ChargeStorageMechanismofMnO2

ElectrodeUsedinAqueousElectrochemicalCapacitorCyclicvoltamogramsin0.1MNa2SO4

at5mV/sof(A)acompositeelectrodecomposedof80%MnO2,7.5%graphite,7.5%acetyleneblack,and5%Teflonand(B)a90%MnO2

and10%PVDF−HFPthinfilmelectrodesupportedonaPtfoil.Chem.Mater.,

2004,

16

,3184–3190electrodemass(μg)amount ofMnO2(moles)voltammetricchargea(C)/(C/g)calculatedcharge(C)bcoulombicefficiency(%)cspecificcapacitance(F/g)A5.0 ± 0.35.75 × 10-80.0056/12500.00551011380B10.0 ± 0.81.15 × 10-70.0106/11900.0111951320C15.0 ± 1.51.73 × 10-70.0148/11000.0166891230D20.0 ± 2.52.30 × 10-70.0156/8750.022270970E25.0 ± 3.82.88 × 10-70.0186/8350.027767930虽然比容量很高，但是仅有最外层的二氧化锰能够参与电化学反应和能量的存储。一般文献里面的高比容量都是精心设计的纳米结构，难以产业化。

Conducting-polymer-basedsupercapacitordevicesandelectrodesTypicalconductivitiesofvariousconductingpolymers.PolymerConductivity(Scm−1)ReferencePolyaniline0.1–5--Polypyrrole10–50--PEDOT300–500--Polythiophene300–400--Variousconductingpolymerstructures.(A)

Trans-poly(acetylene)(B)

cis-poly(acetylene)(C)poly(p-phenylene)(D)polyaniline(PAni)(E)poly(n-methylaniline)(PNMA)(F)polypyrrole(PPy)(G)polythiophene(PTh)(H)3-substitutedpolythiophene(I)poly(3,4-ethylenedioxythiophene)(PEDOT)(J)poly(3-(4-fluorophenyl)thiophene)(PFPT)(K)poly(cyclopenta[2,1-b;3,4-b′-dithiophen-4-one])(PcDT)(L)1-cyano-2-(2-[3,4-ethylenedioxylthienyl])-1-(2-thienyl)vinylene(PThCNVEDT).G.A.Snooketal.JournalofPowerSources196(2011)1–12Theoreticalandexperimentalspecificcapacitancesofconductingpolymers.ConductingpolymerMw(gmol−1)Dopan