MnO/Ccore–shellnanorodsashighcapacityanodematerialsforlithium-ionbatteriesJournalofPowerSourcesFourparts1.Introduction

2.Experiment3.Resultsanddiscussion4.Conclusions

Introductiontransitionmetaloxideshaveattractedgreatattentionasanodematerialsforlithiumionbatteries,dueto1theirhightheoreticalcapacity2safety3lowcost4naturalabundanceSomeobstacle1poorcyclingperformance(largevolumeexpansionduetothegenerationofLi2O)2poorelectronicconductivity(electrodematerialswithdesignednanostructurecanimproveit)MnOshowsrelativelylowelectromotiveforce電動勢(emf)value(1.032

Vvs.Li+/Li)andhighdensity(5.43

g

cm?3).However,thiskindofmaterialhasseldombeenreportedasananodematerialnanocrystallineMnOthinfilm,andMnOpowderasanodehasshownlowoverpotential超電勢andgoodcyclingperformanceInthispaperThepreparedMnO/Ccore–shellnanorodsmuchhigherspecificcapacitythanthatofMnOmicroparticlesandMnO2nanowiresasanodematerialoflithiumionbattery.返回Experiment合成部分MnO/Ccore–shellnanorodsweresynthesizedbythereductionofcarbonprecursorcoatedMnO2nanowires.TheMnO2nanowiresweresynthesizedbyatypicalhydrothermalreactionExperiment表征X-raydiffractionFieldemissionscanningelectronmicroscopy(FESEM）transmissionelectronmicroscopy(TEM)SAEDExperiment電化學試驗部分performingusing2032coin-typecellsassembledinanargon-filledgloveboxslurry:activematerials(70

wt%),acetyleneblack乙炔黑(20

wt%),andpolyvinylidenefluoride聚偏二氟乙烯(PVDF10

wt%)inN-methyl-2-pyrrolidone氮甲基二吡咯烷酮(NMP).TheslurrywasspreadontotheCufoilwithadoctorblade刮墨刀片anddriedat120

°CovernightundervacuumExperimentelectrodeareais1

cm2loadingofactivematerialis1.0–1.2

mg

cm?2

electrolyte:asolutionof1

MLiPF6inethylenecarbonate碳酸亞乙酯(EC)anddimethylcarbonate碳酸二甲酯(DMC)withaweightratioof1:1ExperimentPurelithiumfoilwasusedascounterandreferenceelectrodeCyclicvoltammetry循環(huán)伏安法(CV)Charge–dischargetestingwasperformedintherangeof0.01–3.0

Vspecificcapacity返回Resultsanddiscussion1、MnO2nanowiresweresynthesizedbyhydrothermalreaction.Thecrystalstructureoftheas-preparedMnO2nanowireswasconfirmedbyXRD(Fig.1)Allthediffractionpeakscanbeindexedtothebody-centeredtetragonalα-MnO2phaseResultsanddiscussion2、MnO/Ccore–shellnanorodswereobtainedthroughsinteringthecarbonprecursorcoatedMnO2nanowiresinflowingArcontaining5

vol.%H2.AsshowninFig.1thecrystalstructureofMnO/Ccore–shellnanorodscanbeindexedtotheface-centeredcubicphaseofMnOlowintensitydiffractionpeakintherangeof20–30°islikelyassociatedwiththepresenceofamorphouscarbon無定形碳(originatedfromthedecompositionofthecopolymersurfactant).ResultsanddiscussionResultsanddiscussionFESEM:nanowirestructurewithdiametersrangingfrom20–50nmandThereisnosignificantchangeindiameter

ResultsanddiscussionTEMThenanorodsshowpolycrystallinefeatureandareagglomeratedintobundleswithalengthextendingtoafewhundrednanometers.ThefracturingofthenanowirestructureintonanorodsmaybecausedbythereductionfromMnO2toMnO.Anindividualnanorodconsistsofnanoparticleswithdiametersfrom20nmto30nm.ResultsanddiscussionResultsanddiscussionAllthediffractionringscanbeindexedtotheface-centeredcubicFm-3mcrystalstructure.ResultsanddiscussionHRTEMResultsanddiscussionIntheregionA:thesurfaceoftheMnOcrystal,andthelatticecanbeclearlyresolvedwithad-spacingof0.255

nmforthe(1

1

1)heregionB:carbonlayer,whichpresentsnumerousblackspots,indicatingthatthesurfaceofthenanorodiscoveredwithathinlayerofamorphouscarbon.Ontheedgeofthenanorod,athincarbonlayerwithathicknessof1–2

nmisclearlyvisible.Resultsanddiscussioncyclicvoltammetry(CV)ResultsanddiscussionResultsanddiscussionResultsanddiscussionCyclingperformance

ResultsanddiscussionThisnanorodelectrodeexhibitedhighercapacitythanthatofMnO2nanowireelectrodeafter40cycles.Thegoodelectrochemicalperformanceisaresultofthecombinedadvantagesofthenanorodstructureandtheporouscarboncoatinglayer.ResultsanddiscussionNanosizematerialswithlargesurfaceareacanprovidemoreactivesitesforLi+intercalation/de-intercalationandshortenthediffusionlengthforlithiumionsinthesolidphase.Thenanoporouscarboncoatinglayerwithmesoporescanformamixedconducting3DnetworkthatfacilitatesthemigrationofboththeLi+andthee?,sothattheyreacheachsurfaceoftheMnOnanorods.返回Conclusions1、UsingblockcopolymerF127asthecarbonsource,MnO/Ccore–shellnanorodsweresuccessfullypreparedfromMnO2nanowiresbycalcinationinagas?owof5vol.%H2inAr.2、TheXRDpatternshowsthattheproducthasaface-centeredcubicphasestructure.FESEMandTEMimagesshowthatathincarbonlayerwascoatedonthesurfacesoftheMnOnanorods.Conclusions3、TheMnO/Ccore–shellnanorodelectrodesdeliveredahigherspeci?cdischargecapacitythanMnO2nanowiresafter40