碳纳米材料.ppt

MnO/Ccoreshellnanorodsashighcapacityanodematerialsforlithium-ionbatteriesJournalofPowerSourcesFourparts1.Introduction2.Experiment3.Resultsanddiscussion4.ConclusionsIntroductiontransitionmetaloxideshaveattractedgreatattentionasanodematerialsforlithiumionbatteries,dueto1theirhightheoreticalcapacity2safety3lowcost4naturalabundanceSomeobstacle1poorcyclingperformance(largevolumeexpansionduetothegenerationofLi2O)2poorelectronicconductivity(electrodematerialswithdesignednanostructurecanimproveit)MnOshowsrelativelylowelectromotiveforce电动势(emf)value(1.032Vvs.Li+/Li)andhighdensity(5.43gcm3).However,thiskindofmaterialhasseldombeenreportedasananodematerialnanocrystallineMnOthinfilm,andMnOpowderasanodehasshownlowoverpotential超电势andgoodcyclingperformanceInthispaperThepreparedMnO/CcoreshellnanorodsmuchhigherspecificcapacitythanthatofMnOmicroparticlesandMnO2nanowiresasanodematerialoflithiumionbattery.返回Experiment合成部分MnO/CcoreshellnanorodsweresynthesizedbythereductionofcarbonprecursorcoatedMnO2nanowires.TheMnO2nanowiresweresynthesizedbyatypicalhydrothermalreactionExperiment表征X-raydiffractionFieldemissionscanningelectronmicroscopy(FESEM）transmissionelectronmicroscopy(TEM)SAEDExperiment电化学实验部分performingusing2032coin-typecellsassembledinanargon-filledgloveboxslurry:activematerials(70wt%),acetyleneblack乙炔黑(20wt%),andpolyvinylidenefluoride聚偏二氟乙烯(PVDF10wt%)inN-methyl-2-pyrrolidone氮甲基二吡咯烷酮(NMP).TheslurrywasspreadontotheCufoilwithadoctorblade刮墨刀片anddriedat120CovernightundervacuumExperimentelectrodeareais1cm2loadingofactivematerialis1.01.2mgcm2electrolyte:asolutionof1MLiPF6inethylenecarbonate碳酸亚乙酯(EC)anddimethylcarbonate碳酸二甲酯(DMC)withaweightratioof1:1ExperimentPurelithiumfoilwasusedascounterandreferenceelectrodeCyclicvoltammetry循环伏安法(CV)Chargedischargetestingwasperformedintherangeof0.013.0Vspecificcapacity返回Resultsanddiscussion1、MnO2nanowiresweresynthesizedbyhydrothermalreaction.Thecrystalstructureoftheas-preparedMnO2nanowireswasconfirmedbyXRD(Fig.1)Allthediffractionpeakscanbeindexedtothebody-centeredtetragonal-MnO2phaseResultsanddiscussion2、MnO/CcoreshellnanorodswereobtainedthroughsinteringthecarbonprecursorcoatedMnO2nanowiresinflowingArcontaining5vol.%H2.AsshowninFig.1thecrystalstructureofMnO/Ccoreshellnanorodscanbeindexedtotheface-centeredcubicphaseofMnOlowintensitydiffractionpeakintherangeof2030islikelyassociatedwiththepresenceofamorphouscarbon无定形碳(originatedfromthedecompositionofthecopolymersurfactant).ResultsanddiscussionResultsanddiscussionFESEM:nanowire structure with diameters ranging from 2050 nm and There is no significant change in diameterResultsanddiscussionTEMThenanorodsshowpolycrystallinefeatureandareagglomeratedintobundleswithalengthextendingtoafewhundrednanometers.ThefracturingofthenanowirestructureintonanorodsmaybecausedbythereductionfromMnO2toMnO.Anindividualnanorodconsistsofnanoparticleswithdiametersfrom20nmto30nm.ResultsanddiscussionResultsanddiscussionAllthediffractionringscanbeindexedtotheface-centeredcubicFm-3mcrystalstructure.ResultsanddiscussionHRTEMResultsanddiscussionIntheregionA:thesurfaceoftheMnOcrystal,andthelatticecanbeclearlyresolvedwithad-spacingof0.255nmforthe(111)planes.intheregionB:carbonlayer,whichpresentsnumerousblackspots,indicatingthatthesurfaceofthenanorodiscoveredwithathinlayerofamorphouscarbon.Ontheedgeofthenanorod,athincarbonlayerwithathicknessof12nmisclearlyvisible.Resultsanddiscussioncyclicvoltammetry(CV)ResultsanddiscussionResultsanddiscussionResultsanddiscussionCyclingperformanceResultsanddiscussionThisnanorodelectrodeexhibitedhighercapacitythanthatofMnO2nanowireelectrodeafter40cycles.Thegoodelectrochemicalperformanceisaresultofthecombinedadvantagesofthenanorodstructureandtheporouscarboncoatinglayer.ResultsanddiscussionNanosizematerialswithlargesurfaceareacanprovidemoreactivesitesforLi+intercalation/de-intercalationandshortenthediffusionlengthforlithiumionsinthesolidphase.Thenanoporouscarboncoatinglayerwithmesoporescanformamixedconducting3DnetworkthatfacilitatesthemigrationofboththeLi+andthee,sothattheyreacheachsurfaceoftheMnOnanorods.返回Conclusions1、UsingblockcopolymerF127asthecarbonsource,MnO/CcoreshellnanorodsweresuccessfullypreparedfromMnO2nanowiresbycalcinationinagasflowof5vol.%H2inAr.2、TheXRDpatternshowsthattheproducthasaface-centeredcubicphasestructure.FESEMandTEMimagesshowthatathincarbonlayerwascoatedonthesurfacesoftheMnOnanorods.Conclusions3、TheMnO/CcoreshellnanorodelectrodesdeliveredahigherspecificdischargecapacitythanMnO2nanowiresafter40cycles.However,MnO/Ccoreshellnanorods,despitehavingimprovedspecificcapacityrelativetographite,havecomparablylowcyclabilityrelativetographite.4、Furtherimprovementsarerequiredforpotentialapplicationasanalternativeanodematerialinlithiumionbatteries.