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

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

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

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