Polyaniline-intercalated layered vanadium oxide nanocomposites— application in lithium battery

Polyaniline-intercalated layered vanadium oxide nanocomposites—One-pot hydrothermal synthesis and application in lithium battery

/nanoscale|Nanoscale

Polyaniline-intercalatedlayeredvanadiumoxidenanocomposites—One-pothydrothermalsynthesisandapplicationinlithiumbattery

YupingChen,aGangYang,bZihuiZhang,aXiaoyanYang,aWenhuaHou*aandJun-JieZhu*a

Received15thApril2010,Accepted30thJune2010DOI:10.1039/c0nr00246a

Polyaniline-intercalatedlayeredvanadiumoxidenanocompositesweresuccessfullysynthesizedbyanone-pothydrothermalmethodandcharacterizedbyX-raydiffraction(XRD),scanningelectronmicroscopy(SEM),transmissionelectronmicroscopy(TEM),highresolutiontransmissionelectronmicroscopy(HRTEM),selectedareaelectrondiffraction(SAED),Fouriertransforminfrared

spectroscopy(FT-IR),andRamanspectroscopy.Theeffectsofreactionconditions,suchaspHvalueoftheprecursorsolution,reactiontemperatureandtime,andtheamountofanilineonthestructureandmorphologyoftheobtainedsamples,weresystematicallyinvestigated.Basedontheexperimentalresults,aninsituintercalation-polymerization-exfoliationmechanismwasputforwardforthe

formationoflayerednanocomposites.Theapplicationoftheresultinglayerednanocompositeasthecathodematerialinlithiumbatterywastestedandtheresultsshowedthatthepolyaniline-intercalatedlayeredvanadiumoxidenanocompositepreparedat140 Chadagoodcyclingperformanceandmightactasapromisingcathodematerialforhigh-energy-densityrechargeablelithiumbatteries.

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Introduction

Vanadiumoxidesandtheirrelatedcompoundshavebeeninvestigatedbothextensivelyandintensivelyduetotheirnovelphysicochemicalpropertiesandpotentialapplicationsinlithiumbatteries,1electric eld-effecttransistors2–4andchemicalsensors.5,6Thelayeredstructureandredoxabilityofvanadiumoxidesallowtheinsertionofvariousguestspeciessuchaspoly-mers,leadingtotheformationofhybridmaterialswithamixedvalenceofvanadium(V4+/V5+).7Organic–inorganichybridstructureshavebeendesignedtoachievenewmaterialswithimprovedpropertiesbecauseofthesynergiceffectsoftheirconstituentsatamolecularlevel.8,9Speci cally,theintercalationofconductingpolymersintolayeredinorganichostshasbeenatopicofresearchinterestoverthepasthalfcentury.10–13Amongthefamilyofconductingpolymers,polyanilineisofgreatinterestbecauseitselectricalandopticalpropertiescanbecontrolledbyasimpleandreversibleacid–basedoping–dedopingprocess.14Polyaniline–vanadiumoxidehybridmaterial,anewkindofconductingpolymer/oxidebronze,hasreceivedmuchattentionbecauseofthemixedelectroniccharge-transportproperties10,15,16andpotentialapplicationsinlithiumsecondarybatteries,17–19sensors20andelectrochromicdevices.21Considerableeffortshavebeenmadeonthesynthesisofconventionalpolyaniline–vana-diumoxidehybridmaterialsviainsituoxidativepolymerization/intercalationofanilineinV2O5xerogel15,16,22andthelayer-by-layermethod,23respectively.However,thesemethodsofteninvolvelengthyprocedureswithseveralstepsandneedmore

KeyLaboratoryofMesoscopicChemistryofMOEandKeyLaboratoryofAnalyticalChemistryforLifeScienceofMOE,SchoolofChemistryandChemicalEngineering,NanjingUniversity,Nanjing,210093,P.R.China.E-mail:whou@;jjzhu@b

SchoolofChemistryandMaterialsEngineering,ChangshuInstituteofTechnology,Changshu,215500,P.R.China

Electronicsupplementaryinformation(ESI)available:Experimentaldata.SeeDOI:10.1039/c0nr00246a

a

time.Thus,itisnecessarytodevelopmoreef cientsyntheticmethodstosimplifypreparationproceduresandshortentime.Recently,thehydrothermalandultrasoundroutestopreparepolyaniline–vanadiumoxidehybridnanomaterialshavedrawnmoreattentioninthisregard.Forexample,C.Zhangetal.havereportedaone-stephydrothermalreactionbetweenanilineandperoxovanadicacidtopreparepolyaniline–vanadiumoxidehybridhierarchicalarchitectures.24Maltaetal.havereportedanultrasoundroutetosynthesizehybridvanadium–polyanilinenanowiresstartingfromcrystallineV2O5andaniline.25Never-theless,thesereportsaremainlyfocusedonthespeci cprepa-rationmethods,andthereisstilllittlework,whichisnotsystemized,ontheone-potsynthesisofpolyaniline-intercalatedlayeredvanadiumoxidenanocompositesandtheirapplicationinlithiumbattery.

Herein,wereportanef cientmethodforthecontrolledfabricationofpolyaniline-intercalatedlayeredvanadiumoxidenanocompositesviaafacileone-pothydrothermalroute.TheeffectsofthepHvalueoftheprecursorsolution,reactiontemperatureandtime,andtheamountofanilineonthestructureandmorphologyoftheresultingproductwerediscussedindetailandaninsituintercalation-polymerization-exfoliationformationmechanismwasputforward.Moreover,thepotentialapplica-tionoftheresultinglayerednanocompositeinthelithiumbatterywasinvestigated.

Experimentalsection

Preparationofsamples

Allreagentswereofanalyticalgradeandusedasreceivedwithoutfurtherpuri cation.Distilledwaterwasusedthroughout.Inatypicalprocedure,0.18gofV2O5powderswereaddedinto30mLofdistilledwaterandstirredfor10min.Then,60mLofanilinewereaddedintotheslurrysolution.ThepHvalueoftheprecursorsolutionwasadjustedtoabout3through

Polyaniline-intercalated layered vanadium oxide nanocomposites—One-pot hydrothermal synthesis and application in lithium battery

theadditionof3molLÀ1hydrochloricacid.Theslurrysolutionwasstirredforabout30minandtransferredtoa50mLTe on-linedautoclave.Theautoclavewasheatedto120 Candheldfor24h,thenallowedtocooldowntoroomtemperature.Thedarkgreenprecipitatewascollectedandwashedseveraltimeswithdistilledwaterandanhydrousalcohol,thendriedat60 Cforseveralhoursandkeptforfurthercharacterization.Thesamplessynthesizedat120 Cand180 Carenotedassample1andsample2,respectively.Characterization

Downloaded on 02 December 2010Published on 08 September 2010 on | doi:10.1039/C0NR00246A

AllsampleswerecharacterizedbypowderX-raydiffraction(XRD)onaPhilipsX’PertX-raydiffractometerwithmono- incidentradiation.ThesizechromatizedCuKa(l¼1.5418A)

distributionandmorphologyofallsampleswereanalyzedbyTEMobservationonaJEOLJEM-200CXtransmissionelectronmicroscope.SEMimagesandenergy-dispersiveX-rayspectra(EDS)wereobtainedonaJEOLJEM-6300Felectronmicro-scopeequippedwithEDSdetector.HRTEMimagesweretakenonaJEOL2010microscopeatanacceleratingvoltageof200kV.Fouriertransforminfrared(FT-IR)spectrawereacquiredwithaNicolet6700FT-IRspectrometerusingKBrpellets.RamanspectrawererecordedonaRenishawinViaRamanmicroscope(excitedwithanAr+lineat514nm).Electrochemicaltest

Totesttheobtainedsamplesascathodeinlithiumcells,theas-preparedsamplesweremixedwithcarbonblackandTe onpowder(Dupont)inaweightratioof80:15:5.Lithiumfoil(Aldrich)wasusedasthenegativeelectrode,1MLiPF6inEC:DMC¼1:1wasusedastheelectrolyte,andCelgard2320wasusedastheseparator.Thecellswereassembledinanargon- lledgloveboxwithlessthan5ppmofwaterandoxygen.Cyclingandcharge-dischargeperformancesofthetestingcellswerecarriedoutonabatterytestsystemLANDCT2001Aingalvanostaticmode,operatingataconstantcurrentdensityof29.5mAgÀ1withcontrolledcutoffpotentialsof1.8–3.5V(vsLi/Li+).

Fig.1XRDpatternof(a)V2O5precursor,(b)sample1,and(c)sample

2.

interlayerspacing.Uponintercalation,theinterlayerspacingofV2O5isincreasedfrom0.43to1.4nm,whichisingoodagreementwiththeresultreportedbyHugueninetal.19Ontheotherhand,allthediffractionpeaksofsample2asshowninFig.1ccanbeindexedtothemonocliniccrystallinephaseofVO2(JCPDS81-2392,withthelatticeconstantsofa¼1.129nm,b¼0.3702nm,c¼0.6433nm)andnocharacteristicpeakswereobservedforotherimpurities.

Theenergy-dispersiveX-rayspectra(EDS)weremeasuredtodeterminethechemicalcompositionoftheas-preparedsamples.AsshowninFig.S1(supportinginformation), sample1containsV,O,CandN;however,theatomicratioofVandOcannotbedeterminedbecauseonepeakfortheelementVoverlapswiththepeakfortheelementO.

Fig.2presentsFT-IRspectraofV2O5precursor,sample1,andsample2.InFig.2a,twoabsorptionbandsat3460and1643cmÀ1canbeattributedtothestretchingandbendingmodesofO–Hvibrations,respectively.ItmeansthatsomewatermoleculesareintercalatedintoV2O5layers.26The

absorption

Resultsanddiscussion

Structuralstudy

Thecompositionandphasepurityoftheproductswerechar-acterizedbyXRD.Fig.1showstheXRDpatternsofV2O5precursor,sample1andsample2.ThediffractionpeaksinFig.1acanbereadilyindexedtothepureorthorhombiccrys-tallinephaseofV2O5(JCPDS41-1426,withthelatticeconstantsofa¼1.151nm,b¼0.3565nm,c¼0.4372nm,spacegroupPmmn)andnocharacteristicpeakswereobservedforotherimpurities.Asetofpeakscharacteristicof(00l)re ectionsforthelayeredphaseareobservedinsample1(seeFig.1b),indicatingthatpolyanilineisintercalatedintothelayeredV2O5underhydrothermalconditions.15,16Itisconcludedthatpolyaniline-intercalatedlayeredvanadiumoxidenanocompositescanbeobtainedunderthepresentsyntheticconditions.Thestrongestpeakobservedatthelowest2qanglecorrespondstothe(001)planeofthelayeredV2O5structureandisdirectlyrelatedtothe

Fig.2FT-IRspectraof(a)V2O5precursor,(b)sample1,and(c)sample2.

Polyaniline-intercalated layered vanadium oxide nanocomposites—One-pot hydrothermal synthesis and application in lithium battery

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bandsbetween400and1050cmÀ1canbeindexedtovarious(group)vibrationsofV–Otype.26Thecharacteristicbandsitu-atedat1023cmÀ1isrelatedtotheV]Ostretching,thebandslocatedat598and824cmÀ1canbeattributedtothesymmetricandasymmetricvibrationalmodesoftheV–O–VstretchinginV2O5,respectively.15,27,28InFig.2b,thetypicalbandsofpoly-anilinecanbeobservedclearly.Thepeaksintherangeof3200–3500cmÀ1(e.g.3231cmÀ1)areduetotheN–Hstretchingvibrationsoftheleucoemeraldinecomponent.Thecharacteristicpeaksat1575cmÀ1and1487cmÀ1areassignedtotheC]Cstretchingmodeofquinoidandbenzenoidrings,respectively.Thepeaksat1323cmÀ1and1248cmÀ1correspondtothestretchingvibrationsofC–NandC]N,respectively.Thepeakat1138cmÀ1isassignedtothein-planebendingofC–H.20,29Theappearanceofallthesepeaksindicatesthatprotonatedpoly-anilineisformedafterthereactionofinitialV2O5precursorwithanilineunderhydrothermalconditions.ThecharacteristicbandofV]Ostretchingat995cmÀ1(Fig.2c)and1023cmÀ1(Fig.2a)areoftheoxidationandreductionstatesofthevanadiumV4+andV5+oxides,respectively.30TheshiftoftheV]Ostretchingvibrationmodefrom1023cmÀ1intheV2O5precursorto1002cmÀ1inthenanocompositesuggeststhatV5+isreducedtoV4+partially.

Fig.3showstheRamanspectraoftheV2O5precursor,sample1,andsample2.AllsamplesshowthetypicalRamanscatteringbandsoforthorhombicV2O5,whichisingoodagreementwiththosedescribedintheref.31and32.Thelow-wavenumberpeaksat143and189cmÀ1correspondtotheexternal[VO5]–[VO5]modes,indicatingtheretentionoflongrangeorderinthesestructures.31Thepeaksat686and521cmÀ1canbeattributedtoantiphasebridgingV–OandchainingV–Ostretchingmodes,characteristicsoforthorhombicV2O5.31,32Thestrongpeakat988cmÀ1isattributedtothestretchingmodeofthevanadylV]Omoiety.33Morphology

Fig.4showstheSEMimagesoftheV2O5precursor,sample1andsample2.TheV2O5precursorhasthemorphologyofirregularnano akes.Ontheotherhand,sample1,polyaniline-

Fig.4SEMimagesof(a),(b)V2O5precursor,(c),(d)sample1,and(e),(f)sample2.

intercalatedlayeredvanadiumoxidenanocomposite,hasthemorphologyofwhitefungusself-assembledfromthenanosheets.Asshowninthemagni edSEMimages(Fig.4d),thethicknessofthenanosheetsisbetween10and20nm,andthetypicallateraldimensionofthenanosheetsisintherangeofhundredsofnanometrestoseveralmicrometres.Inaddition,theSEMresultsalsosuggestthatthereisnobulkdepositionofpolyanilineonthesurfaceofmicrocrystallites.The2Dwhitefungus-likenano-structurecanalsobeseenclearlyinthecorrespondingTEMimage(Fig.5a).ThethicknessandlateraldimensionofthenanosheetsareconsistentwiththeSEMresult.Theelectrondiffractionpattern(insetofFig.5a)indicatesthatthepolyani-line-intercalatedlayeredvanadiumoxidenanocompositeisquasi-crystalline,whichisquitesimilartotheresultreportedbyZhangetal.22Moresigni cantly,theHRTEMimageinFig.5bshowsthehierarchicalarchitecturesoftheobtainedlayerednanocomposite,suggestingthattheinsituredoxintercalativepolymerizationbyhydrothermaltreatmentistopotacticandthelayeredhoststructurestillremainsunchanged.ItcanalsobeseenfromtheHRTEMimagethattheobtainednanocompositeconsistsofseveralconductingpolymernanosheetsandthelowscatteringpowercausedbrightcontrastforwhitelines,eachwithawidthof$1.5nmbetweentwodarkfringesofhostlayers,whichisingoodagreementwiththeinterlayerspacingd001¼1.4nmevaluatedfromXRD.Thus,fromtheHRTEMimageandXRD,itcanbeconcludedthathighlycrystallinevanadiumoxidelayersareseparatedalternativelybypolyanilinenanosheetsinthehybridnanocomposite.

Formationmechanisms

Fig.3Ramanspectraof(a)V2O5precursor,(b)sample1,and(c)sample

2.

TheinsituintercalationandpolymerizationreactionofanilinewithlayeredV2O5wascarriedoutunder

hydrothermal

Polyaniline-intercalated layered vanadium oxide nanocomposites—One-pot hydrothermal synthesis and application in lithium battery

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Fig.7SEMimagesoftheas-preparedsamplesobtainedatdifferentpHvalues(T¼120 C,t¼24h).(a)pH¼1,(b)pH¼2,(c)pH¼4,(d)pH¼5.

Fig.5(a)TypicalTEMimageand(b)HRTEMimageofsample1(insetof(a):SAED

pattern).

conditions.Tofurtherunderstandtheformationmechanismofpolyaniline–intercalatedlayeredvanadiumoxidenano-composite,thein uencesofreactionparameters,suchasthepHvalueoftheprecursorsolution,reactiontemperatureandtime,andtheamountofanilineonthestructureandmorphologyoftheresultingsampleswereinvestigatedindetail.

TheXRDpatternsoftheas-preparedsamplesobtainedatdifferentpHvaluesareshowninFig.6.Thediffractionpeaksofallsamplescanbeindexedtothelayeredphaseofthepolyani-line-intercalatedvanadiumoxidenanocomposite.Fig.7showsthecorrespondingSEMimagesoftheas-preparedsamplesobtainedatdifferentpHvalues.AsshowninFig.7a,thesamplesynthesizedatpH¼1hasthemorphologyofnanosheets,andsomebulkdepositionofpolyanilineonthesurfaceofthe

Fig.6XRDpatternsoftheas-preparedsamplesobtainedatdifferentpHvalues(T¼120 C,t¼24h).(a)pH¼1,(b)pH¼2,(c)pH¼4,(d)pH¼

5.

nanosheet.ThesamplessynthesizedatpH¼2,4,5haveasimilarmorphology,butthenanosheetsarenotassembledinorder(Fig.7b,c,d).Itisworthnotingthat,whenthepHvalueoftheprecursorsolutionisadjustedto7and9throughadding3molLÀ1ammonia,noprecipitatecanbeobtainedafterreactionat120 Cfor24h.Itrevealsthatanacidicenvironmentisanindispensableconditiontosynthesizepolyaniline-intercalatedvanadiumoxidenanocomposites.Ontheonehand,thepHvalueoftheprecursorsolutionin uencesthespeciesandstatesofvanadate.Accordingtoref.34,whenthevanadiumconcentra-tionis3.3Â10À2molLÀ1,andthepHis1,2,3,4and5,thecorrespondingmainphasesareattributedtothe occulated,dispersed,dispersed, occulatedand occulatedribbonsamples,respectively.SothesamplesobtainedatpH1,4and5aremorecompactlyassembledthanthesamplesobtainedatpH2and3.WhenthepHis7and9,themainphasesareattributedtopolyvanadates,sonoprecipitatecanbeobtainedafterreaction.Ontheotherhand,thepHvalueoftheprecursorsolutionalsoin uencesthechargeofthecolloidandthenthecondensationmodeandrate.WhenthepHwaslowerthan2.6(isoelectricpointofV2O5sol),thechargeofthecolloidwaspositiveasH+wasabsorbedatthesurfaceofthecolloid,andtheolationreactionwasdominantandgaverisetothecorner-sharingchainpoly-mers.35ThelowerthepHvalue,thehigherthecondensationrate.WhenthepHwashigherthan2.6,thechargeofthecolloidwasnegativeasOHÀwasabsorbedatthesurfaceofthecolloid,andtheoxolationreactionwasdominantandledtotheformationofedge-sharingdoublechains.35ThehigherthepHvalue,thehigherthecondensationrate.Inaddition,consideringthatthepolyanilinesobtainedatdifferentpHvalueshavedifferentdopingdegrees,theas-preparedsamplesobtainedatdifferentpHvaluesmayhavedifferentelectronicconductivitiesandfurtherdifferentperformancesinlithiumionbatteries.

Fig.8andFig.9showXRDpatternsandSEMimagesoftheas-preparedsamplessynthesizedatdifferentreactiontempera-tures,respectively.Thediffractionpeaksofthesamplessynthe-sizedat80 C,100 C,120 Cand140 Ccanbeindexedtothelayeredphaseofthepolyaniline-intercalatedvanadiumoxidenanocomposite.AsshowninFig.9aandFig.9b,thesamplesynthesizedat120 Chasthemorphologyofwhite

fungus

Polyaniline-intercalated layered vanadium oxide nanocomposites—One-pot hydrothermal synthesis and application in lithium battery

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Fig.8XRDpatternsoftheas-preparedsamplesobtainedatdifferentreactiontemperatures(pH¼3,t¼24h).(a)80 C,(b)100 C,(c)120 C,(d)140 C,(e)160 C,(d)180

C.

Fig.10XRDpatternsoftheas-preparedsamplesobtainedat120 Cfordifferentreactiontimes(pH¼3).(a)15min,(b)30min,(c)1h,(d)15

h.

Fig.9SEMimagesoftheas-preparedsamplesobtainedatdifferentreactiontemperatures(pH¼3,t¼24h).(a)120 C,(b)140 C,(c)160 C,(d)180

C.

Fig.11SEMimagesoftheas-preparedsamplesobtainedat120 Cfordifferentreactiontimes(pH¼3).(a)15min,(b)30min,(c)1h,(d)15h.

self-assembledfromthenanosheets,whilethesamplesynthesizedat140 Chasthemorphologyofshaleself-assembledfromthenanosheets.Asthetemperatureisincreasedto160 C,theXRDpattern(Fig.8e)revealsthattheobtainedsampleiscomposedoftwodifferentphases,yeredphaseofthepolyaniline-inter-calatedvanadiumoxidenanocompositeandmonocliniccrys-tallinephaseofVO2(JCPDS81-2392),andtheSEMimage(Fig.9c)showsithasamixedmorphologyofnanosheetsandnanobelts.Whenthetemperatureisfurtherincreasedto180 C,allthediffractionpeaksoftheresultingsamplecanbeindexedtothemonocliniccrystallinephaseofVO2(seeFig.8f)andthesampleshowsthemorphologyofuniformnanobelts(Fig.9d).Theseresultssuggestthatanappropriatereactiontemperatureiscrucialfortheformationofthepolyaniline-intercalatedlayeredvanadiumoxidenanocomposite.

Fig.10showstheXRDpatternsoftheas-preparedsamplessynthesizedat120 Cfordifferentreactiontimes.Thesamplesynthesizedat120 Cfor15mincanbeindexedtothepureorthorhombiccrystallinephaseofV2O5(Fig.10a),andthelayeredphaseofthepolyaniline-intercalatedvanadiumoxidenanocompositeappearedinthesampleobtainedafter30min(Fig.10b).AsshowninFig.10cand10d,whenthereactiontime

isfurtherincreasedto1handthereafter,alltheBraggpeaksoftheobtainedsamplesareconsistentwiththoseofthepolyaniline-intercalatedvanadiumoxidenanocomposite.Itrevealsthatthepolyaniline-intercalatedvanadiumoxidehybridmaterialcanbesynthesizedwithin1h.Fig.11showsthecorrespondingSEMimagesoftheas-preparedsamplesobtainedatdifferentreactiontimes.AsshowninFig.11a,thesampleobtainedatareactiontemperatureof120 Cfor15minhasthemorphologyofnano-plates,similarwiththeprecursorV2O5butwithadecreasedthickness.Asthereactiontimeisincreasedto30min,theobtainedsamplehasamixedmorphologyofnanoplatesandnanosheets(Fig.11b).Withprolongingthereactiontime,thesampleobtainedat60minpresentsahomogeneousmorphologyofnanosheets(Fig.11c).Thesampleobtainedafter15hhasthemorphologyofnanosheetsandthenanosheetsbecomemoreuniformandordered(Fig.11d).

Fig.12andFig.13showXRDpatternsandcorrespondingSEMimagesoftheresultingsamplessynthesizedinthepresenceofdifferentamountsofanilineat120 Cfor24h.AsshowninFig.12,allthesamplescanbeindexedtothelayeredphaseofthepolyaniline-intercalatedvanadiumoxidenanocomposite.InFig.13,itcanbefoundthattheresultingsamplespresentthemorphologyofnanosheetsandthethicknessofthenanosheets

is

Polyaniline-intercalated layered vanadium oxide nanocomposites—One-pot hydrothermal synthesis and application in lithium battery

ofvanadiumoxide,leadingtotheformationofalayerednano-compositewithamixedvalenceofV4+/V5+,wherethenegativelychargedoxidehostlayerscounter-balancethesemi-oxidizedguestpolyaniline.16,19Whentheamountofanilineandreactiontemperaturewereincreased,theintercalationofaniliniumcationsintotheinterlayerspaceofV2O5wasfavored,thusthethicknessoftheobtainedlayerednanocompositenanosheetswasdecreased.Thedetailedformationmechanismofthepolyaniline-intercalatedlayeredvanadiumoxidenanocompositenanosheetsneedsfurtherinvestigation.Electrochemicalproperties

Theinitialchargeanddischargepro lesoftheV2O5precursorandpolyaniline-intercalatedlayeredvanadiumoxidenano-compositeareshowedinFig.14.Thedischargepro leofpureV2O5showsadistinctplateauduetostructuralchangesfroma-LixV2O5to3-LixV2O5,d-LixV2O5andg-LixV2O5.1Onthecontrary,thepotentialdecreasesmoresmoothlydownto$2.7Vforthenanocomposite,displayingaminorplateauaround2.5V.AsimilarcontinuousdecreaseinpotentialhasalsobeenobservedfortheV2O5xerogel,andforotherconductivepoly-mer/V2O5nanocomposites,37wherethecommonstructuralfeatureistheenhancedseparationofvanadiumoxidelayersduetothepresenceofinterlayeredmoleculessuchaspolyanilineorH2O.Thecellfabricatedwiththesampleobtainedat140 Cshowsgoodelectrochemicalbehavior,witha rstdischargecapacityof239mAh$gÀ1,whichisnearly87%ofthetheoreticalcapacityofV2O5(276mAh$gÀ1,n¼2).38Bycomparison,themaximumdischargecapacityofthecellfabricatedwithV2O5precursorisonly114.5mAh$gÀ1.Theimprovedperformanceofthelayeredhybridmaterialispresumablyduetothelargerseparationbetweenvanadiumoxidelayers,leadingtoanenhanced‘‘bidimensionality’’.Furthermore,theintercalationofpolyanilinemayimprovetheelectronicconductanceoftheobtainednanocomposite,beingbene cialfortheincreaseofcapacity.Theelectronicconductanceofsample1wasmeasuredas3.2Â10À3S$cmÀ1,whichisnearly50timeshigherthanthatofpristineV2O5(6.78Â10À5S$cmÀ1).37Itisworthmentioningthatthepolyaniline-intercalatedlayeredvanadiumoxidenano-compositerevealsalargercapacityduringthe rstchargethanthe rstdischarge.ItcanbeattributedtothepresenceofV4+

,

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Fig.12XRDpatternsofpolyaniline-intercalatedvanadiumoxidehybridnanocompositesobtainedinthepresenceofdifferentamountsofaniline(pH¼3,T¼120 C,t¼24h).(a)30mL,(b)60mL,(c)120mL,(d)240mL.

Fig.13SEMimagesofpolyaniline-intercalatedvanadiumoxidehybridnanocompositesobtainedinthepresenceofdifferentamountsofaniline(pH¼3,T¼120 C,t¼24h).(a)30mL,(b)60mL,(c)120mL,(d)240m

L.

decreasedfrom30–40nmto10–20nmwiththeincreaseoftheamountofaniline,whichissimilartothatreportedinref.22.Basedontheabove-mentionedresults,apossibleformationmechanismofpolyaniline-intercalatedlayeredvanadiumoxidenanocompositeisputforwardasfollows:Intheearlystageofthereaction,theanilinemonomerwas rstconvertedtotheanili-niumcationinanacidicenvironment.Sincethevanadiumoxidepresentsahighaf nityfornitrogenatedcompounds(throughN–H+/O]Vbonds)becauseofitsBrønsted-acidcharacter,36theaniliniumcationswereintercalatedintotheinterlayerspaceofV2O5duetoanacid–baseinteractionandsubjectedtooxidativepolymerizationbetweenthelayers.Astheinsituintercalationandpolymerizationproceeded,thebulklayeredV2O5wasexfoliatedtoacertainextenttoformnanosheetsofthepoly-aniline-intercalatedlayeredvanadiumoxidenanocomposite.Thewhitefungusmorphologyoftheresultingnanocompositewasself-assembledfromthenanosheets.Theintercalationandoxidativepolymerizationofanilinemodi edthebandstructure

Fig.14Firstcharge(solidline)anddischarge(dottedline)pro lesofthecellsfabricatedwith(a)pureV2O5,(b)sampleobtainedat140 C(pH¼3,t¼24

h).

Polyaniline-intercalated layered vanadium oxide nanocomposites—One-pot hydrothermal synthesis and application in lithium battery

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Fig.15Cyclingperformancesofthecellsfabricatedwithsamplesobtainedatdifferentreactiontemperatures(a)140 C,(b)160 C,(c)120 C,(d)180 Cand(e)pureV2O5.

nmandatypicallateraldimensionintherangeofhundredsofnanometrestoseveralmicrometres.Thein uenceofseveralreactionparametersonthestructureandmorphologyoftheresultingsampleswasdiscussed.Itwasfoundthatacidicenvi-ronmentandproperreactiontemperaturearevitalforthesynthesisofthepolyaniline-intercalatedlayeredvanadiumoxidenanocomposite.Aninsituintercalation-polymerization-exfolia-tionmechanismwasputforwardfortheformationoflayerednanocompositesbasedontheexperimentresults.Themethodreportedhereisfastandsimple,andisalsoapplicableforthesynthesisofotherpolymer-intercalatedlayerednanocompositessuchaspolypyrrole-intercalatedandpoly(3,4-ethyl-enedioxythiophene)-intercalatedlayeredvanadiumoxidenano-composites.Thelithiumintercalationperformancesoftheobtainednanocompositeweremeasured.Theresultssuggestthatthepolyaniline-intercalatedlayeredvanadiumoxidenano-compositeobtainedat140 Ccanactasapromisingcathodematerialforhigh-energy-densityrechargeablelithiummicro-batteries.

whichcouldbeeasilyoxidizedbyanelectrochemicalmethod,asalreadyreportedinthecaseofconductivepolymer/V2O5hybrids.39,40

Charge-discharge(chronopotentiometric)experimentswereperformedaccordingtoref.18totestthespeci ccapacitiesoftheobtainedsamples.Fig.S2 showssuchdataforV2O5(dottedline)andpolyaniline-intercalatedvanadiumoxidelayerednanocompositesobtainedat140 C(solidline).Thespeci ccapacitiesofthesesamplescalculatedfromtheexperimentaldataare134.1mAh$gÀ1and167.6mAh$gÀ1,respectively.Thesevaluesarenotaslargeasthosereportedinref.18.Nevertheless,thenanocompositepreparedat140 Cshowsasuperiorspeci ccapacityandcharge-dischargebehaviorincomparisonwiththeparentmaterial,whichisinagreementwiththetestedresultofthefabricatedcell.

Goodcyclingperformanceisadesirablefeatureinbatteryapplications.Recently,muchworkwasconcentratedonimprovingthecyclingperformanceofV2O5throughdoping.41,42Fig.15showsthecyclingperformancesofcellsfabricatedwithpureV2O5andtheresultingsamplesobtainedatdifferentreac-tiontemperatures,paredwithpureV2O5,thesamplesobtainedat140 Cand160 Cexhibitmuchbettercyclingabilityandhigherreversiblecapacity.After30cycles,thecapacityofthecellfabricatedwiththesampleobtainedat140 Cdecreasesto209mAh$gÀ1atarateof29.5mA$gÀ1,whichis87%ofitsinitialcapacity.Thiscomparativeanalysisclearlysuggeststhattheobtainedlayerednanocompositemayactasapromisingcathodematerialinhigh-energy-densityrechargeablelithiummicrobatteries.

Acknowledgements

Theauthorsgreatlyappreciatethe nancialsupportoftheNationalNaturalScienceFoundationofChina(GrantNo.20773065,20635020),NationalBasicResearchProgram(973project)(GrantNo.2007CB936302)andModernAnalysisCenterofNanjingUniversity.

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Conclusion

Insummary,polyaniline-intercalatedlayeredvanadiumoxidenanocompositeshavebeensynthesizedbyinsituintercalationandpolymerizationofanilinewithbulkV2O5underhydro-thermalconditions.Theresultingpolyaniline-intercalatedvana-diumoxidelayerednanocompositeshavehybridhierarchicalarchitectureswithamorphologyofwhitefunguswhichareself-assembledfromthenanosheetswithathicknessbetween10–20

Polyaniline-intercalated layered vanadium oxide nanocomposites—One-pot hydrothermal synthesis and application in lithium battery

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