关于磷酸铁锂的英文文献含中文翻译.docx
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关于磷酸铁锂的英文文献含中文翻译
Preparationandcharacterizationofcarbon-coatedLiFePO4cathodematerialsforlithium-ionbatterieswithresorcinol–formaldehydepolymerascarbonprecursor
YachaoLan,XiaodongWang⁎,JingweiZhang,JiweiZhang,ZhishenWu,ZhijunZhang⁎
KeyLaboratoryforSpecialFunctionalMaterials,HenanUniversity,Kaifeng475004,China
abstract
articleinfoArticlehistory:
Received8February2011
Receivedinrevisedform26May2011Accepted3June2011
Availableonline12June2011Keywords:
Lithiumironphosphate
Resorcinol–formaldehydepolymerLithium-ionbattery
LiFePO4/Ccompositesweresynthesizedbytwomethodsusinghome-madeamorphousnano-FePO4astheironprecursorandsolublestarch,sucrose,citricacid,andresorcinol–formaldehyde(RFpolymerasfourcarbonprecursors,respectively.Thecrystallinestructures,morphologies,compositions,electrochemicalperformancesofthepreparedpowderswereinvestigatedwithXRD,TEM,Raman,andcyclicvoltammogrammethod.TheresultsshowedthatemployingsolublestarchandsucroseasthecarbonprecursorsresultedinadeficientcarboncoatingonthesurfaceofLiFePO4particle,butemployingcitricacidandRFpolymerasthecarbonprecursorsrealizedauniformcarboncoatingonthesurfaceofLiFePO4particle,andthecorrespondingthicknessesoftheuniformcarbonfilmsare2.5nmand4.5nm,respectively.WhenRFpolymerwasusedasthecarbonprecursor,thematerialshowedthehighestinitialdischargecapacity(138.4mAhg−1at0.2Catroomtemperatureandthebestrateperformanceamongthefourmaterials.
©2011ElsevierB.V.Allrightsreserved.
1.Introduction
LiFePO4isanattractivecathodematerialforlithium-ionbatteriesbecauseofitshightheoreticalcapacityof170mAhg−1,environ-mentalbenign,andhighthermalstability.However,itspoorelectricconductivityoflessthan10−13Scm−1limitsitsbatteryperformance[1],suchasthedramaticdecreaseinpoweratahighcurrentdensity,whichisthemaindrawbacktocommercialuse.ToovercomethelowelectricconductivityofLiFePO4,manyeffectiveapproacheshavebeenintroduced,includingmetalsubstitution[2–5],metalpowdercom-pounding[6],andconductivecarboncoating[7–15].Amongthem,thepreparationofLiFePO4/carboncomposite(LiFePO4/Cisoneoftheattractivewaystoimprovetheelectricconductivityofthefinalproductbyformingagoodconductionpath.Furthermore,carboncanbealsousedasareductant,whichcanreduceFe3+ionstoFe2+ions.Itshouldbenotedthatmanystudiesinvolvingthesynthesisofnano-sizedLiFePO4employFe2+saltsasprecursors[3,16–20],suchasFeC2O4·2H2Oand(CH3COO2Fe,whichareexpensive.Therefore,itisnecessarytousecheapmaterialsandaconvenientmethod.
Here,wereportthesynthesis,characterizationandelectrochemicaltestofLiFePO4/Ccompositespreparedbytwomethodsusinghome-madeamorphousnano-FePO4astheironprecursorandvariousorganicsascarbonprecursors.ThetwomethodsusingFePO4asstartingmaterialarecheapandenvironmentallybenignfortheproductionofLiFePO4material.Particularly,wepresentanovelmethodtosynthesizeauniform
carbonfilmcoatedLiFePO4cathodematerials.ThismethodinvolvedaninsitureactionofresorcinolandformaldehydeonthesurfaceofamorphousFePO4.Atroomtemperature,electrochemicaltestsshowedthatthismaterialexhibitedaninitialdischargecapacityof138.4mAhg−1at0.2Candagoodcyclingpropertyat0.5and1.0Crate,respectively.2.Experimental
2.1.Preparationofamorphousnano-FePO4
Amorphousnano-FePO4waspreparedbyspontaneousprecipita-tionfromaqueoussolutions.AnequimolarsolutionofH3PO4wasaddedtoasolutionofFe(NO33·9H2Oat60°CunderstirringandgivenamountsofPEG-400assurfactant.Thenammoniawater(NH3·H2Owasslowlyaddedtothemixedsolutionundervigorousstirringandamilk-whiteprecipitateformedimmediately.ThepHofthesolutionwaskeptat2.0.Theprecipitatewasfilteredandwashedseveraltimeswithdistilledwater.Afterdryinginvacuumovenat120°Cfor12h,yellowish-whiteamorphousFePO4wasobtained.2.2.PreparationofLiFePO4/C
TwomethodswereusedtopreparetheLiFePO4/Ccompositesinthisstudy.
Arheologicalphasemethod[21]wasemployedtosynthesizeLiFePO4/Ccomposite.StoichiometricamountofamorphousFePO4,LiOH·H2Owereusedasthestartingmaterials.Thecarbonprecursors
PowderTechnology212(2011327–331
Wang.
0032-5910/$–seefrontmatter©2011ElsevierB.V.Allrightsreserved.doi:
ContentslistsavailableatScienceDirect
PowderTechnology
journalhomepage:
www.elsevier.com/locate/powtec
Inatypicalsynthesis,0.10gofCTABwassolvedin30mlofdistilledwatersolutionundercontinuousstirring.Subsequently,1.52gFePO4·3H2O,0.055gresorcinol(Rand0.10mlformaldehyde(Fweresuccessivelyadded.Whenthetemperatureofwaterbathwasupto85°C,LiOH·H2Owasadded.Themixturewaskeptstirredupinthedarkfor2h,driedinanovenat120°Cfor6h,heatedat350°Cfor1hinargonflow,treatedat750°Cfor12hinargonflow,andfinallygroundtoobtaintheLiFePO4/Ccomposites(denotedassampleD.
ThesefoursamplesandtheircorrespondingparametersarelistedinTable1.ThecarboncontentsofthesampleswerecalculatedbythelossonignitionofthefourLiFePO4/Ccompositesinair.
2.3.Characterization
Thermogravimetric(TGanddifferentialthermalanalysis(DTAanalyseswereconductedwithanEXSTAR6000thermalanalysissystemataheatingrateof10°Cmin−1.ThepowderX-raydiffraction(XRD,X'PertProMPD,PhilipsusingCuKaradiationwasemployedtoidentifythecrystallinephaseofthepreparedmaterials.RamanspectrumwasrecordedonaRenishawRM-1000MicroscopicRamanspectrometerwith457.5nmexcitationrequiringa10mWpoweratroomtemperature.Low-magnificationandhigh-magnificationTEMimagesweretakenonaJEM-2010transmissionelectronmicroscope(usinganacceleratingvoltageof200kV.
Electrodeswerefabricatedfromamixtureofpreparedcarbon-coatedLiFePO4powders(80wt.%,carbonblack(12wt.%,andpolyvinylidenefluorideinN-methylpyrrolidinon(8wt.%.TheslurrywasspreadontoAlfoilanddriedinvacuumat120°Cfor12h.Thecarbon-coatedLiFePO4loadingwas2mgcm−2intheexperimentalcells.Thecellswereassembledinanargon-atmosphere-filledglovebox.Theelectrolytewas1MLiPF6inamixtureofethylenecarbonate(ECanddimethylcarbonate(DMC(1:
1volume.Thecellsweregalvanostaticallychargedanddischargedatavoltagerangeof2.5–4.2VwithLANDbatterytestingsystematroomtemperature.CyclicvoltammogramswererunonanIM6impedanceandelectrochemical
measurementsystem(Zahner,Germanyatascanrateof0.1mVs−1between2.5and4.0V.
3.Resultsanddiscussion
TheTEMimagesoftheamorphousnano-FePO4wereshowninFig.1.Themorphologyoftheas-preparedFePO4isanirregularparticlewithanaveragediameterof30nm.Mostoftheparticlesconnectedtoeachotherbecauseoftheirhighsurfaceenergywhichresultsfromtheirsmallsizes.
Fig.2ashowstheTG/DTAcurvesoftheFePO4·3H2Opowderwithaheatingrateof10°C/minfromroomtemperatureto850°Cinair.OntheDTAcurvenear150°C,thereisaverystrongendothermicpeak,associatingwiththesharpweightlossontheTGcurve,whichisrelatedtothequickdehydrationofFePO4·3H2O.During150–550°C,26.3%weightlossontheTGcurveindicatesthesloweliminationofresidualH2OinFePO4·3H2O,exactlycorrespondingtothelossofcrystallinewaterofFePO4·3H2O.Andoneexothermicpeakisdisplayedatahighertemperatureof590°C,whichisnotaccompa-niedbyappreciableweightlossintheTGcurve,indicatingthetransformationoftheamorphousFePO4tohexagonalFePO4crystal.TheXRDpatternsofFePO4·3H2ObeforeandaftercalcinationhavebeeninvestigatedinFig.2b.AsillustratedinpatternA,itcanbeseenthatthereisnoevidenceofdiffractionpeaksbeforecalcination,indicatingthesynthesizedFePO4·3H2Oisjustamorphous.WhileforthecalcinatedFePO4·3H2Oat600°Cfor6hinair,itexhibitsstrongandnarrowpeaksrevealingawell-crystallizedmaterialinpatternB.AllofthediffractionpeaksofthepreparedFePO4areindexedtoasingle-phasehexagonalstructurewithaP3121spacegroupandwithoutanyimpurities,whichisingoodagreementwiththestandardcard(JCPDScardno:
72–2124.
Table1
CarbonprecursorsandresidualcarboncontentofsamplesA,B,CandD.
SamplesABCD
5.1Fig.1.TEMimagesofthepreparedamorphousnano-FePO4.
328Y.Lanetal./PowderTechnology212(2011327–331
TheXRDdiffractionpatternsofLiFePO4/CpowderspreparedwithdifferentcarbonprecursorswereshowninFig.3.Allpeakscanbeindexedasasinglephasewithanorderedolivinestructureindexedtotheorthorhombicspacegroup,Pnmb(JCPDScardno.83–2092.TheobtainedlatticeparametersaresampleA:
a=10.2956Å,b=6.0367Å,andc=4.7001Å,sampleB:
a=10.1992Å,b=6.0483Å,and
c=4.6971Å,sampleC:
a=10.2472Å,b=6.0208Å,andc=4.6882ÅandsampleD:
a=10.3372Å,b=5.9993Å,andc=4.6932Å,respec-tively.Thereisnoevidenceofdiffractionpeaksforcarbon,thoughsomeamorphousmassesandfilmsattachedtotheLiFePO4particleswereobservedfromTEMimages(seeFig.4.Thisindicatesthecarboncontentsareverylow.
MorphologiesoftheseLiFePO4/CcompositeswereshowninFig.4.ItisobviousthatthesamplesshowdifferentcarbondistributiononLiFePO4particlesurface.FromFig.4a,c,eandg,weobservedthatthesampleswerecomposedofagglomeratedparticleswhosesizesrangefrom50to300nm.FromFig.4bandd,thereisnotenoughcarboncoatingtospreadthroughoutthesubstrateparticles.IncontrasttosampleAandsampleB,thereare
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