Polyaniline-intercalated layered vanadium oxide nanocomposit(6)

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+

,

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

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).