PEG高温固相法合成-英文

JournalofAlloysandCompounds456(2008)461–465AsoftchemistrysynthesisroutineforLiFePO4–CusinganovelcarbonsourceL.N.Wanga,X.C.Zhana,Z.G.Zhanga,K.L.Zhanga,b,∗aCollegeofChemistryandMolecularSciences,WuhanUniversity,Wuhan430072,ChinabCentreofNanoscienceandNanotechnologyResearch,WuhanUniversity,Wuhan430072,ChinaReceived17August2006;receivedinrevisedform13February2007;accepted20February2007Availableonline23February2007AbstractAsanovelcarbonsource,polyethyleneglycol(PEG;meanmolecularweightof10,000)wasadoptedtoprepareLiFePO4–Ccathodematerialbyaverysimplesoftchemistrymethod,whichwascalledrheologicalphasereactionbyus.X-raydiffraction(XRD)revealthatthecrystallizedLiFePO4powdercanbesynthesizedeasilybyrheologicalphasereactionatarelativelowtemperature(400◦C).Scanningelectronmicroscopy(SEM)resultsindicatethatafterthedecompositionofPEG,activematerialandporousstructurecarbonwereleftintheresultantproducts.Aninitialdischargecapacityof162and139mAhg−1wasachievedfor500◦CsampleatroomtemperaturewithCratesof0.06C(10mAg−1)and1C(170mAg−1),respectively.Thesatisfactoryinitialdischargecapacityandsuperiorratecapacityshouldattributetotheporousconductivecarbonstructureandthesoftsynthesisprocess.©2007ElsevierB.V.Allrightsreserved.Keywords:Cathodematerial;LiFePO4;PEG;Rheologicalphasereaction1.IntroductionDuetoitsoverwhelmingadvantagesoflowtoxicity,goodthermalstabilityandrelativelyhightheoreticalcapacity,olivinetypeLiFePO4,whichwasfirstintroducedasalithiumbatteriescathodematerialbyPadhietal.appearsasapotentialcandidatetobeusedaspositiveelectrodeinnextgenerationofLi-ionbatteries[1–5].Asamaterial,however,LiFePO4isaninsulator,whichseri-ouslylimitsitsratecapabilityinlithiumcells.Itshowshighelectrochemicalpropertiesonlyatlowcharge–dischargeratesowingtoitslowelectronicconductivityandlowlithiumionmotionability[6,7].Therefore,researchonthisinsulatingcom-poundwasuptonowmostlydevotedtoenhancethecomposite’sconductivitybymetaldoping[8,9]orcoatingwiththeelectron-icallyconductivelikecarbon,metalandmetaloxide[10–12].OtherpossiblemeansofimprovingtherateperformanceofLiFePO4materialsarethoseofenhancingitsionic/electronicconductivitybyoptimizationofparticleswithsuitableprepara-tionprocedures.Inadditiontothetraditionalsolid-statereaction∗Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](K.L.Zhang).synthesisroutine,alternativesynthesisprocessesincludingsol–gel,hydrothermal,co-precipitation,microwaveheating,etc.havedevelopedcontinually[11,13–15].Inthiswork,anexampleofpreparingLiFePO4materialwithnano-sizedfineparticlesbyemployinganovelcarbonsourceofpolyethyleneglycol(PEG)withaverysimplesoftchem-istrymethod—therheologicalphasereactionmethod[16–19]isprovided.Thesolidreactantsarefullymixedinapropermolarratio,madeupbyaddingtherequiredamountofwaterorothersolventtoasolid–liquidrheologicalbodyinwhichthesolidparticlesandliquidsubstanceareuniformlydistributed.Thenafterreactionundersuitableconditions,theproductisobtained.Underthesolid–liquidrheologicalstate,manysubstanceshavenewreactionproperties.Theresultantpowderspreparedbythismethodoftenshowexcellentelectrochemicalperformance.Themicrostructureandtherateperformanceoftheas-preparedLiFePO4–Cwereinvestigated.Also,anexcellentorganiccarbonsource—PEGwasintroduced.2.ExperimentalLi2CO3,FeC2O4·2H2O,NH4H2PO4andpolyethyleneglycol(meanmolec-ularweightof10,000)powderswereusedasthestartingmaterialsbyrheologicalphasereaction.Theyweremixedthoroughlybygrinding.Thenappropriate0925-8388/$–seefrontmatter©2007ElsevierB.V.Allrightsreserved.doi:10.1016/j.jallcom.2007.02.103462L.N.Wangetal./JournalofAlloysandCompounds456(2008)461–465amountofde-ionizedwaterwasaddedtogetarheologicalbody,whichwastheprecursorofLiFePO4–C.Finally,theresultingprecursorwasheatedinAratmospheretogetthepowdersofLiFePO4–C.Thermaldecompositionandcrystallizationtemperaturesoftherheologicalbodyprecursorwereinvestigatedbythermogravimetryanddifferentthermalanalysis(TG/DTA),whichwereperformedbetweenambientand1000◦Cwithheatingrateof20◦Cmin−1undertheflowingAr.X-raydiffraction(XRD)pro-filesofthesamplewerecarriedoutonaShimadzuXRD-6000diffractometerusingCuK1radiation.Theparticlessizedistributionwasdeterminedbytheopticalparticlesizeanalyzer(Mastersizer2000,England).Themorphologywasobservedusingscanningelectronmicroscopy(SEM)withSirionFEGSEM.Elementalcompositionofthecompoundpowder(Li,FeandP)wasdeterminedbyinductivelycoupledplasma(ICP)withatomicemissionspectroscopy(ICP-AES,modelIRIS,TJA,USA),andtheamountofcarbonwasdeterminedbyelementanalyzer(FLASH112SERIES,Italy).EDAXwasalsousedtofurtherexaminetheelementalcomposition.Forthecellmeasurement,thepreparedsamplewasexaminedbyasimulatedcellsystem.TheLiFePO4–Cmaterialwasmixedwith20%carbonblackand5%PTFE.Themixturewaspressedontonickelgridasthecathode,purelithiumastheanode,1mol/LLiClO4(EC:DMC=1:1)astheelectrolyte,aCelguard2400(American)micro-porousmembranefortheseparator.TheassembliesofthecellprototypeswerecarriedoutinanAr-filledglovebox(Mikrouna,Super1220/750,China)withbothwaterandoxygenconcentrationslessthan5ppm.The