H2V3O8与石墨烯复合材料应用到锂离子电池.docx

H2V3O8与石墨烯复合材料应用到锂离子电池.docx

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H2V3O8与石墨烯复合材料应用到锂离子电池

DOI:

10.1002/cplu.201300331

SynthesisofH2V3O8/ReducedGrapheneOxideCompositeasaPromisingCathodeMaterialforLithium-IonBatteries

KaiZhu,[a]XiaoYan,[a]YongquanZhang,[a]YuhuiWang,[a]AnyuSu,[a]XiaofeiBie,[a]DongZhang,[a]FeiDu,[a]ChunzhongWang,[a,b]GangChen,[a,b]andYingjinWei*[a]

Introduction

Inrecentyears,electricitygenerationfromwindandsolarenergyhasimprovedgreatlywithbecauseofthecontributionsmadebyglobalscientists.[1]Inaddition,hybridelectricvehicles（HEVshavebeenrecognizedasreplacementsforfuelvehiclesinthenearfuturetoreducefossilfuelconsumptionandCO2emissions.Allthesegreen-energytechniquesneedtobesup-portedwithlarge-scaleenergy-storagedevices.Itisgenerallyacceptedthatlithium-ionbatteriesarethemostsuitableenergy-storagesystemsamongthevariouspossibilities.[2,3]However,itisdifficultforthetraditionalLiCoO2cathodetomeettheincreasingdemandsoflarge-scalelithium-ionbatter-iesintheaspectsofenergy/powerdensities,safety,andprice.[4,5]Therefore,thesearchfornewcathodematerialshasbecomeaseriousissueforthenextgenerationoflithium-ionbatteries.

VanadiumoxidessuchasV2O5,VO2,V2O5·nH2Oxerogel,b-AgVO3,andLiV3O8,withtypicalopen-layeredstructures,allowtheintercalationofguestmoleculesorcationsintothelayers.[6,7]Inlithium-ionbatteries,theseopen-layeredstructuresoffermuchhigherspecificenergiesthanmanyothercathodematerialssuchasLiCoO2andLiFePO4.Anothervanadiumoxide,H2V3O8,hasbeenreportedasapromisingcathodema-terialsince2006.[8]Inrecentyears,severalattemptshavebeen

madetoprepareH2V3O8nanomaterialstoimproveitselectro-chemicalproperties.[8–12]IthasbeenreportedthatH2V3O8nanobeltsexhibitaveryhighinitialdischargecapacityof373mAhgÀ1.[10]However,thecyclelifeandratecapabilityofthematerialaregreatlyrestrictedbecauseofitslargeirreversi-blecapacityandlowelectronicconductivity.[9]Theelectronicconductivitiesofelectrodematerialscanbeimprovedthroughtheircombinationwithhighlyconductivecarbonaceousmate-rials.[13,14]Recently,compositeelectrodesthatinterconnectnanostructuredelectrodematerialswithgraphenehaveat-tractedmuchattention.[15]Ingeneral,thegrapheneinthecompositeelectrodescanactbothasconductivechannelsandasanelasticbuffertoaccommodatethevolumechangethatoccursduringrepeatedlithiumuptakeandremoval,simultane-ouslypreventingtheaggregationofnanoparticlesandthecrackingorcrumblingoftheelectrodematerials.[15–18]There-fore,itseemstobeanidealreinforcingcomponentforcompo-siteelectrodes.Manygraphene-basedelectrodematerialssuchasV2O5/graphene,[19]V2O5·nH2Oxerogel/graphene,[20]TiO2/gra-phene,[21]SnO2/graphene,[22]Co3O4/graphene,[23]andFe3O4/gra-phene[24]havebeenreportedsofar,allofwhichshowedim-provedelectrochemicalpropertieswithrespecttotheirpristinecounterparts.However,tothebestofourknowledge,nonano-structuredH2V3O8/graphenecompositematerialhasyetbeenreported.

Herein,aH2V3O8/reducedgrapheneoxide（RGOcompositecathodewasfabricatedthroughasimpleapproach,asillustrat-edinFigure1a.GrapheneoxidespreparedthroughamodifiedHummersmethodweremixedwithHVO4formedfromthere-actionofV2O5andH2O2.Underhydrothermalconditions,thecompositesself-assembledintoH2V3O8/RGOnanostructures,inwhichtheelectrontransportthroughtheH2V3O8nanowireswasimprovedowingtothepresenceofthehighly

conductive

[a]K.Zhu,X.Yan,Y.Zhang,Y.Wang,A.Su,Dr.X.Bie,Dr.D.Zhang,Dr.F.Du,

Prof.Dr.C.Wang,Prof.Dr.G.Chen,Prof.Dr.Y.Wei

KeyLaboratoryofPhysicsandTechnologyforAdvanceBatteriesMinistryofEducation,CollegeofPhysics

JilinUniversity,Changchun130012（P.R.ChinaFax:

（+86431-85155126E-mail:

yjwei@[b]Prof.Dr.C.Wang,Prof.Dr.G.Chen

StateKeyLaboratoryofSurperhardMaterialsJilinUniversity,Changchun130012（P.R.China

CHEMPLUSCHEMFULL

PAPERS

RGOnanosheets（Figure1b.Moreover,RGOsuppressedthestructuraldegradationofH2V3O8duringcharge/discharge,im-provingtheelectrochemicalperformanceofthematerialsignif-icantly.

ResultsandDiscussionThephaseandcompositionoftheas-obtainedH2V3O8and

H2V3O8/RGOproductswereanalyzedbyXRDasdepictedin

Figure2.AlltheXRDpeakscanbeindexedreadilytotheor-thorhombiccrystallinephaseofH2V3O8（spacegroup:

Pnam.[25]

Nocharacteristicpeaksfromimpuritiesofothervanadium

oxidesaredetected,whichindicatesthattheproductsconsist

ofapureH2V3O8phase.Thecalculatedlatticeparametersof

theproductsarea=9.373（3,b=16.939（7,c=3.649（6for

thepristinesample,anda=9.353（1,b=16.932（0,c=3.646（4fortheH2V3O8/RGOcomposite,whichareingoodagreementwithpreviouslyreportedvalues（JCPDS,No.85-2401.Theslightdifferencesinthelatticeparametersmaybecausedbydifferenthydrothermalconditionswith/withouttheadditionofgrapheneoxidesolution.Inaddition,asmalldif-fractionpeakcanbeobservedat26.58forH2V3O8/RGO,whichisabsentforthepristinematerial.Thisadditionalpeakcanbeindexedtothedisordered002stackinglayersofRGO,[19,26]indi-catingthatthecompositeisfabricatedsuccessfullythroughthepresentsyntheticroute.ForthedeterminationoftheexactamountofRGO,thermogravimetricanalysis（TGAwasper-formedonH2V3O8andtheH2V3O8/RGOcomposite（Figure3.

ForthepristineH2V3O8,theweightlossof4.4wt%before6008CiscausedbythedecompositionofH2V3O8.Alarger

weightlossof10.7wt%isobservedforH2V3O8/RGO,which

maybeattributedtothecombustionofRGOtogetherwiththedecompositionofH2V3O8.Onthebasisoftheseresults,themasscontentofRGOintheH2V3O8/RGOcompositeisestimat-edtobe6.3wt%.Figure4a,bshowsSEMimagesoftheH2V3O8andH2V3O8/RGOproducts.Thepristinesampleconsistsofalargenumberofuniformnanowireswithahighaspectratio:

50–200nminwidthandseveralmicrometersinlength.FromtheSEMimageofH2V3O8/RGO,itisapparentthattheH2V3O8nano-wiresaredispersedontheRGOlayer.Thegrapheneoxides,withabundantfunctionalgroupssuchashy-droxyl,carboxyl,andcarbonylgroups,attacheasilyontothesurfaceofH2V3O8andareconvertedtore-ducedgrapheneoxidesduringhydrothermaltreat-ment.Inthemeantime,theH2V3O8nanowireshelppreventtheRGOfromunitinginthereductionpro-cess.ThisnanoarchitecturedwrappinglayerofRGOsheetsformedontheH2V3O8surfacecanactasanelectronicconductiveskin.Forfurthercharacteriza-tionofthemicrostructureoftheH2V3O8/RGOcompo-site,TEMwasperformedasshowninFigure4c.ThisshowsclearlythattheH2V3O8nanowiresareanch-oredintimatelyontheRGOsheets.Inthiscase,itisanticipatedthatoncetheelectronsarriveat

RGOFigure1.aSchematicofthesynthesisroutefortheH2V3O8andH2V3O8/RGOmaterials,andbtheidealelectrontransportationpathwayintheH2V3O8/RGO

composite.

Figure2.XRDpatternsofpristineH2V3O8andtheH2V3O8/RGOcompositecomparedwith

thestandardXRDpatternforH2V3O8

（PDF#85-2401.

Figure3.TGAcurvesofpureH2V3O8andtheH2V3O8/RGOcomposite.

theycantransferquicklytotheH2V3O8nanowires.Thus,anim-provedelectricalconductivityofthecompositewouldbeex-pected.Thehigh-resolutionTEMimage（Figure4dexhibitsalatticefringecorrespondingtoad-spacingof0.33nm,whichisinagreementwiththed101spacingofH2V3O8.ThelocalstructuresofthematerialswerestudiedfurtherthroughRamanscatteringexperiments,asshowninFigure5,togetherwiththatofpuregrapheneoxide.NotethattheRamanpatternsofH2V3O8/RGOandgrapheneoxidearemulti-pliedbytenbecauseoftheirratherweakpeakintensities.ThebasicstructuralunitsofH2V3O8arecomposedofVO6octahedraandVO5trigonalbipyramids,whichformtheV3O8layersbysharingedges.[11]TheRamanspectraofH2V3O8canbeana-lyzedintermsofinternalandex-ternalvibrations（similarlytothoseofmostvanadiumoxides.Theinternalmodescanbede-scribedasstretchingandbend-ingvibrationsoftheVÀObonds.Thesevibrationsgiverisetothehigh-frequencyRamanbandsabove200cmÀ1.TheexternalmodescanbeviewedasrelativemotionsoftheV3O8layers,whicharelocatedatlowfre-quenciesbelow200cmÀ1.TheinternalandexternalvibrationsofpristineH2V3O8andH2V3O8/RGOappearatthesameposi-tionswithinanerrorof2cmÀ1,indicatingthattheRGOinthecompositedoesnotinfluencethelocalstructureofH2V3O8.TherearetwoprominentRamanpeaksat1330cmÀ1and

1601cmÀ1

fortheH2V3O8/RGO

composite,whichareabsentforthepristineH2V3O8.Thesead-ditionalpeakscorrespondtotheDandGbandsofRGO.[24]The

intensityratiooftheDtoGbands（ID/IGisameasureofdisor-derincarbon-basedmaterials.TheID/IGvalueofgrapheneoxideiscalculatedtobe0.86.Afterthereductionofgrapheneoxide,defectsintheresultantRGOincreaseowingtofragmen-tationalongthereactivesite,alargernumberofedges,andsoon.ThisresultsinbroaderDandGbands,andtheID/IGratioof

RGOincreasesto1.15.Inaddition,thereisadistinctivepeakat876cmÀ1,whichiscausedbytheVÀClinkagebetweenRGOandH2V3O8.Accordingtopreviousreports,suchabridgebe-tweentheactivematerialandRGOmayproduceasynergisticeffectthatimprovesthelithium-storagebehavior.[27]Further-more,thescatteringbackgroundoftheH2V3O8/RGOcompositeisverystrong,andtheRamanpeaksaremuchweake