碳纳米材料ppt课件.ppt

MnO Ccore shellnanorodsashighcapacityanodematerialsforlithium ionbatteries JournalofPowerSources 1 Fourparts 1 Introduction2 Experiment3 Resultsanddiscussion4 Conclusions 2 Introduction transitionmetaloxideshaveattractedgreatattentionasanodematerialsforlithiumionbatteries dueto1theirhightheoreticalcapacity2safety3lowcost4naturalabundance 3 Someobstacle1poorcyclingperformance largevolumeexpansionduetothegenerationofLi2O 2poorelectronicconductivity electrodematerialswithdesignednanostructurecanimproveit 4 MnOshowsrelativelylowelectromotiveforce电动势 emf value 1 032Vvs Li Li andhighdensity 5 43gcm 3 However thiskindofmaterialhasseldombeenreportedasananodematerialnanocrystallineMnOthinfilm andMnOpowderasanodehasshownlowoverpotential超电势andgoodcyclingperformance 5 InthispaperThepreparedMnO Ccore shellnanorodsmuchhigherspecificcapacitythanthatofMnOmicroparticlesandMnO2nanowiresasanodematerialoflithiumionbattery 返回 6 Experiment 合成部分MnO Ccore shellnanorodsweresynthesizedbythereductionofcarbonprecursorcoatedMnO2nanowires TheMnO2nanowiresweresynthesizedbyatypicalhydrothermalreaction 7 Experiment 表征X raydiffractionFieldemissionscanningelectronmicroscopy FESEM transmissionelectronmicroscopy TEM SAED 8 Experiment 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anddriedat120 Covernightundervacuum 9 Experiment electrodeareais1cm2loadingofactivematerialis1 0 1 2mgcm 2electrolyte asolutionof1MLiPF6inethylenecarbonate碳酸亚乙酯 EC anddimethylcarbonate碳酸二甲酯 DMC withaweightratioof1 1 10 Experiment PurelithiumfoilwasusedascounterandreferenceelectrodeCyclicvoltammetry循环伏安法 CV Charge dischargetestingwasperformedintherangeof0 01 3 0Vspecificcapacity 返回 11 Resultsanddiscussion 1 MnO2nanowiresweresynthesizedbyhydrothermalreaction Thecrystalstructureoftheas preparedMnO2nanowireswasconfirmedbyXRD Fig 1 Allthediffractionpeakscanbeindexedtothebody centeredtetragonal MnO2phase 12 Resultsanddiscussion 2 MnO Ccore shellnanorodswereobtainedthroughsinteringthecarbonprecursorcoatedMnO2nanowiresinflowingArcontaining5vol H2 AsshowninFig 1thecrystalstructureofMnO Ccore shellnanorodscanbeindexedtotheface centeredcubicphaseofMnOlowintensitydiffractionpeakintherangeof20 30 islikelyassociatedwiththepresenceofamorphouscarbon无定形碳 originatedfromthedecompositionofthecopolymersurfactant 13 Resultsanddiscussion 14 Resultsanddiscussion FESEM nanowirestructurewithdiametersrangingfrom20 50nmandThereisnosignificantchangeindiameter 15 Resultsanddiscussion TEM 16 Thenanorodsshowpolycrystallinefeatureandareagglomeratedintobundleswithalengthextendingtoafewhundrednanometers ThefracturingofthenanowirestructureintonanorodsmaybecausedbythereductionfromMnO2toMnO Anindividualnanorodconsistsofnanoparticleswithdiametersfrom20nmto30nm Resultsanddiscussion 17 Resultsanddiscussion Allthediffractionringscanbeindexedtotheface centeredcubicFm 3mcrystalstructure 18 Resultsanddiscussion HRTEM 19 Resultsanddiscussion IntheregionA thesurfaceoftheMnOcrystal andthelatticecanbeclearlyresolvedwithad spacingof0 255nmforthe 111 planes intheregionB carbonlayer whichpresentsnumerousblackspots indicatingthatthesurfaceofthenanorodiscoveredwithathinlayerofamorphouscarbon Ontheedgeofthenanorod athincarbonlayerwithathicknessof1 2nmisclearlyvisible 20 Resultsanddiscussion cyclicvoltammetry CV 21 Resultsanddiscussion 22 Resultsanddiscussion 23 Resultsanddiscussion Cyclingperformance 24 Resultsanddiscussion ThisnanorodelectrodeexhibitedhighercapacitythanthatofMnO2nanowireelectrodeafter40cycles Thegoodelectrochemicalperformanceisaresultofthecombinedadvantagesofthenanorodstructureandtheporouscarboncoatinglayer 25 Resultsanddiscussion NanosizematerialswithlargesurfaceareacanprovidemoreactivesitesforLi intercalation de intercalationandshortenthediffusionlengthforlithiumionsinthesolidphase Thenanoporouscarboncoatinglayerwithmesoporescanformamixedconducting3DnetworkthatfacilitatesthemigrationofboththeLi andthee sothattheyreacheachsurfaceoftheMnOnanorods 返回 26 Conclusions 1 UsingblockcopolymerF127asthecarbonsource MnO Ccore shellnanorodsweresuccessfullypreparedfromMnO2nanowiresbycalcinationinagas owof5vol H2inAr 2 TheXRDpatternshowsthattheproducthasaface centeredcubicphasestructure FESEMandTEMimagesshowthatathincarbonlayerwascoatedonthesurfacesoftheMnOnanorods 27 Conclusions 3 TheMnO Ccore shellnanorodelectrodesdeliveredahigherspeci cdischargecapacitythanMnO2nanowiresafter40cycles However MnO Ccore shellnanorods des