不同導電添加劑對電化學的影響

Int.J.Electrochem.Sci.,11(2016)6808–6818,doi:10.20964/2016.08.26InternationalJournalofELECTROCHEMICALSCIENCEEffectofDifferentConductiveAdditivesontheElectrochemicalPropertiesofMesoporousMnO2NanotubesXiaoWang,XiaoliLiu,KeChen*CollegeofMaterialsScienceandEngineering,ChongqingUniversity,Chongqing400044,PRChina*E-mail:Received:30April2016/Accepted:5June2016/Published:7July2016MnO2asanenvironmentalbenignitymaterialhasbeenofgreatinterestforsupercapacitorsduetoitsuniquepropertiesleadingtoimprovedperformances.HereinwedescribetheeffectsofdifferentconductiveagenttoimprovetheelectrochemicalpropertiesofMnO2nanotubes.Threetypicalconductiveadditives:carbonblack,carbonnanotubes,andgraphenearechosentomixwithMnO2nanotubesintheworkingelectrodes.ThespecificconductivitiesofMnO2@carbonblackparticleselectrode,MnO2@carbonnanotubeselectrode,andMnO2@grapheneelectrodeatthecurrentdensity1Ag-1are244.8Fg-1,190.2Fg-1,and114.1Fg-1respectively.Furthermore,MnO2@carbonnanotubeselectrodepossessesanelectrochemicalcapacitanceashighas297.5Fg-1atthecurrentdensity0.5Ag-1,whichcanbeputdowntothesesoftthinnanotubescanbeintertwinedwitheachothertoformapowerfulnetworktoprovideconduction.Inprinciple,thehighspecificcapacitanceandstablestructureoftheMnO2@carbonnanotubeselectrodeensuresitspotentialfortheapplicationsinsupercapacitorsandothermicroelectronics.Keywords:graphene;carbonblacks;carbonnanotubes;manganesedioxidenanotubes;supercapacitors1.INTRODUCTIONWiththerapiddevelopmentofthetechnologies,energygrowstoacrisistotheworld.Thetechnologicalthereuponadvancessuchasfullcells,supercapacitorsforhigh-performanceenergystoragedevices.Itiswell-documentedthatthehighpowerdensities,fastcharge-dischargerates,andexcellentcyclicstabilitiescanbeownedbyusingsupercapacitors[1-5].Themechanismofsupercapacitorscanbedividedintotwodifferenttypes.Theelectricaldouble-layerisfromchargeseparationtoobtainelectrostaticstorage,whilepseudocapacitorsbasedonthereversibleFaradicreactions[6-8].Int.J.Electrochem.Sci.,Vol.11,20166809Transitionmetaloxidesprovideopportunitiestodesignelectrodesforsupercapacitorswithhighperformance.Asfortransitionmetaloxide,suchasRuO2,ithashightheoreticalcapacity;however,itstoxicfeatureandhighcostlimititsutility[9-10].MnO2asanenvironmentalbenignitymaterialhasbeenofgreatinterestforsupercapacitorsduetoitsuniquepropertiesleadingtoimprovedperformances.However,itspoorelectricalconductivityistheissuetouseinpracticalsupercapacitors[11-14].Ananoscaleapproachtoelectrodesforsupercapacitorshasbeenmorepopularinrecentyears,variousmorphologieshavebeenreportedbefore,suchasnanosheetarrays,nanoparticals,core/shellnanostructures,tubulararraysandsoon[4,12,15-17].Recentresearcheshaveproventhathollowstructurescanimprovetheelectrochemicalpropertiesforsupercapacitorscomparedtosolidnanostructures[18].TheuseofMnO2nanotubesaselectrodeinourexperimenthasmanyadvantages:(i)improvedelectricalconductivityduetothehighporosity(ii)lowinternalresistanceduetohollow1Dconductivepaths,(iii)largeactiveareaandabilitytowithstandcyclicchangesinvolume[19-20].InordertoexploretheimprovementofdifferentconductiveagentforMnO2electrodes,someresearchalsohavedonebyusingdifferentconductiveadditivestoimprovetheelectricalconductivities,especiallybyaddingcarbonnanostructuresandgraphenetomodifythecapacitorpropertiesandcyclingstabilities.Inaddition,carbonnanostructuresandgraphenearebothallotropesofcarbon,andthecompositionsandmorphologiesoftheconductiveadditivesdefinetheelectrodeinspecificcapacitance,dischargerate,andcyclelifeaswell[10,21-25].Porouscarbonblack(CB)particlesasthe0Dconductiveagentarewidelyusedelectrodematerialsduetotheirlargesurfacearea,moderatecost,andrelativelygoodelectricalpropertiesinspecificcapacitance,dischargerate,andcyclingstability[25-26].Carbonnanotubespossessacylindricalhollow1Dnanostructurewhichwasmadeupwithcarbonsheetsinthesizeofseveralatoms,andultimatelydeterminesitspropertiesofrapidcharge-dischargerate[27-28].Meanwhile,graphenehasatheoreticalspecificsurfaceareaof2630m2g-1duetoits2Dhoneycomblatticewhicharrangedintoaplanarmonolayerofcarbonatoms,andhasaveryhighintrinsicelectricalconductivityandchemicalstability[29-30].However,atypicalcomparativeresearchhadnotbeenreported.Herein,wefirstlyreportthatthedifferentconductiveadditivesforMnO2nanotubes,andtheirapplicationsaselectrodesforsupercapacitor.MnO2nanotubesweresynthesizedbyetchingfromCuO@MnO2composites,what’smore,thereactionliquidafteretchingevenprovideCu2+toobtainotherCuandCuoxidenanostructuresforsupercapacitors[31-32].Carbonblackparticles,graphene,andcarbonnanotubeswereintroducedtotheuniquehollow1Dnanostructureisexpectedtodeliverexceptionalelectrochemicalperformance.Theresultsindicatethattheconductiveadditivesindeedinfluencetheperformanceofthesupercapacitorandthegraphenerepresentthebestintermsofenergycapacityandstability.2.EXPERIMENTAL2.1PreparationofMnO2nanotubesMnO2nanotubeswerepreparedbyetchingmethodfromtheCuO/MnO2core-shellarchitecture[33].Briefly,CuO/MnO2core-shellarchitecturewascorrodedby1MH2SO4andtheresultingMnO2Int.J.Electrochem.Sci.,Vol.11,20166810nanotubeswererefinedandpurifiedviasuccessivecentrifugationinwaterandalcohol,thendriedunder60oCinair[30].2.2HomogeneousmixtureofMnO2nanotubesandconductiveadditivesforelectrodesThemixtureofMnO2nanotubesandconductiveadditivesissimplebuteffective.First,acertainamountofMnO2nanotubesandconductiveadditivesweretakeninthebeaker,andmarkedA,B,Crespectivelyonthebeakerwhichaddedcarbonblack,carbonnanotubes,graphene.Then,suitableamountofalcoholwereintroducedtothebeakerforultrasonicprocess.Andfolloweddrying,themixingisfinished,andthehomogeneousmixtureispreparedwiththeproportion7:2,what’smore,thepolyvinylidenefluoride(PVDF)inN-methyl-2-pyrrolidone(NMP)wasintroducedinthehomogeneousmixturewiththeproportion9:1forpreparingworkingelectrodes.2.3.CharacterizationandElectrochemicalmeasurementsMorphologiesweretakenonthefocusedionbeam(ZeissAurigaFIB/SEM).ThechemicalcompositionsweremeasuredbypowderX-raydiffraction(XRD,D/max2500,Cu,K).TostudytheresponseofMnO2nanotubeswithdifferentconductiveadditives,athree-electrodesystemincludingaworkingelectrode(as-preparedproducts),aplatinumelectrodeandareference(saturatedcalomel)electrodewasapplied.Alloftheelectrochemicaltestingincludingcyclicvoltammetry(CV),Galvanostaticcharge-discharge(GCD)andelectrochemicalimpedancespectroscopy(EIS),wereusinganelectrochemicalworkstation(CHI660E)inthe1MNa2SO4aqueoussolution.CVtechniqueswerecarriedoutonthepotentialrangefrom-0.2Vto0.8Vwithrate5-100mVs-1,GCDmeasurementswereperformedbyusingcurrentdensitiesrangebetween0.5and10Ag-1inthesamepotentialrange.AndEISwerecalculatedwiththefrequencyrange10mHz-100kHz.3.RESULTSANDDISCUSSION3.1.StructureandmorphologyThetransformationofthenanostructuretoformMnO2nanotubes,asshowninFig.1,involvestwomajorsteps:(i)Cunanowires(Nws)actedasthetemplate,andtheMnO2nanosheetsgrowonthetemplatebyhydrothermaland(ii)theCuNwswereetchingbyH2SO4(aq)toobtaintheMnO2nanotubes.WecanseefromFig.1aandbthatthesizeofCuNwsisabout100nm,andthewireshavesofttexture.MorphologyofthecompositeofMnO2nanosheetsdecoratedonCuNwsisshowninFig.1candd,suggestingthatthehydrothermalcanroughenthesmoothtextureofthenanostructure.Thesampleincreaseditswidthfrom100nmto800nmduetoCuNwshassurfacescoveredbynanosheets.However,thelengthgetshortencorrespondingly,whichmayduetotheCuNwswerecorrodedpartlyintheprocessofhydrothermalsynthesisandledtothefracture.Fig.1eandfistheSEMofMnO2nanotubes,whichrevealedthattheacidtreatmentcausedslightlychangesontheInt.J.Electrochem.Sci.,Vol.11,20166811structureofthecomposite,thelengthgetshortenandthewidthgetwidenfurther.Butthesamplepreserveditsrelativelyroughsurfacemorphologyandonecanrealizetexturalporosityonthetubesurfaces.However,completenessofetchingneedsfurtherexploration.Figure1.TypicalSEMimagesoftheCunanowires(a-b),CuO@MnO2nanostructure(c-d)andtheMnO2NTssamples(e-f)atdifferentmagnifications.X-raydiffraction(XRD)wasconductedtofirmlydeterminatethefinenessofMnO2nanatubes.AsshowintheFig.2a,thediffractionpeaksat12.7,18.1,25.6,28.7,37.6,42.0,49.9,59.5,65.5,72.5,and77.5ocanbeassignedtoMnO2(JCPDSno.72-1982),whichcorrespondto(110),(200),(220),(310),(121),(301),(411),(260),(002),(631)and(402)reflections,respectively.NootherpeakswereobservedinMnO2nanotubes.ThisdataindicatethatthesuccessfulsynthesisoftheMnO2nanotubesInt.J.Electrochem.Sci.,Vol.11,20166812viaouretchingprocess.Fig.2b-dshowstheSEMimageofMnO2electrodewithcarbonblack,carbonnanotubes,graphenerespectively,andthecorrespondingSEMimagesoftheconductiveadditiveswereshownintheinnerplot.TheSEMimageinFig.2bofferstheinformationonthemixtureofMnO2@carbonblackelectrode.TheMnO2nanotubesprovidethebasematerialforcarbonblacktoadjoin,andcarbonblackparticlesweregatheredbetweenthespacesofMnO2nanotubes.Asallweknowsthatcarbonblackisthemostcommonconductiveadditiveusedinelectrochemicalfieldduetoitshighcapacitance,however,itspropertyofeasytoaggregationandpoint-to-pointmethodincontactwithactivitymaterialsmaylimititsefficiency.Fig.2cdepictstheSEMimageofMnO2nanotubeswithcarbonnanotubes,whichindicatesthatthecarbonnanotubeshavemoreflexiblestructurethanMnO2nanotubesandandtwinearoundtheMnO2nanotubestoformapowerfulpathwayforchargetransfer.Themicrostructuresofcarbonnanotubesarecylindricalanddecoratewithmultiaperturestructureasreportedbyandtheuniquestructurebenefitforthechargestoragebytheelectricdouble-layerprinciple[27].Thegoodentanglednetworkalsocontributestothemechanicalpropertiesoftheelectrode.FromFig.2d,wecanseethatMnO2nanotubeswereinterspersedwithplatestructureofgraphene,however,accordingtotherealdataofourwork,theMnO2nanotubesshowtheuniformlywidthabout800nmwhichisrelativelylargecomparedwithgraphenenanosheets,andthesheetsbetweentheMnO2nanotubescouldnotbuildaneffectiveconductivenetwork.(a)(b)(c)(d)Figure2.(a)XRDpatternofMnO2NTsandSEMimagesofMnO2nanotubeswithgraphene(b),carbonblack(c),andcarbonnanotubes(d),andtheinnerplotshowstheSEMimageofpureconductiveadditives.Int.J.Electrochem.Sci.,Vol.11,20166813Fig.3schematicallyillustratesthemixingprocessoftheMnO2nanotubueswithdifferentconductiveadditivesforworkingelectrodes.Theintimatemixtureswerepreparedbyultrasound,andMnO2nanotubeswereblendedwithcarbonblack(0D),carbonnanotubes(1D),andgraphene(2D),alltheconductiveadditiveswerewelldispersed.However,themorphologiesofvariouscarbonsmaterialshaveasignificantimpactonthechargetransfer.Obviously,thecarbonblackparticlesconnecteachotherwithpointcontact,whichcertainlylimitsitsconduction.Whatmore,easyaggregationofcarbonblackparticlesleadtoaffectthecharge-dischargerate.Carbonnanotubesasafibrousadditivecannotonlyformaneffectiveconductivenetwork,butalsosustainthewholenanostructurewiththebindingforcefromthenetwork.What’smore,thegraphenenanosheetshave2Dplatestructures,butitseemsunconspicuousinimprovingelectrochemicalpropertiesduetotheimpropersize.Andthedifferencebetweenthreekindsofelectrodesinelectrochemicalpropertieswillbediscussedinthenextpart.Figure3.SchematicillustrationshowsthemixingprocessofMnO2nanostructurewithdifferentconductiveadditives.3.2.ElectrochemicalperformanceofelectrodeswithdifferentconductiveadditivesToidentifytheeffectiveconnectandchargestransferbetweenMnO2nanotubesandconductiveadditives,theelectrochemicalperformanceoftheMnO2nanotubeswithdifferentconductiveagentelectrodeswereinvestigated.Herein,thethree-electrodesystemusingPtfoilasthecounterelectrode,andnormalcalomelelectrodeasthereferenceelectrode.CVcurvesofdifferentconductiveadditivesat50mVs-1aredisplayedinFig.4a,therectangularshapeofthethreecurvesweresosimilar,whichInt.J.Electrochem.Sci.,Vol.11,20166814indicatedthatalltheelectrodeshaveexcellentstability.ThisresultwasattributedtothelargespecificcapacitanceofMnO2nanotubes.(a)(b)(c)(d)Figure4.(a)Cyclicvoltammogramsoftheseelectrodesatthescanrateof50mVs-1ina1MNa2SO4aqueouselectrolyte;(b)Charge-dischargecurvesofMnO2electrodesatcurrentdensitiesof2Ag-1;(c)TheelectrochemicalimpedancespectrumoftheMnO2electrodeswithdifferentconductingadditivesinthefrequencyrangefrom0.01Hzto10kHzand(d)SpecificcapacitanceofMnO2nanostructuresmeasuredwithdifferentconductingadditives.However,theconductiveadditivesimpactthecapacitancetoalargeextent.MnO2@grapheneelectrodeshowsadistinctdecreaseinthecapacitance,suggestingthatgraphenesheetshadaggregatedandimpactitsspecificsurfaceareaandelectrochemicalproperties.BasedontheresearchbyJiangetal.indicatedthatthespecificcapacitorofpuregrapheneusedinsupercapercitorsat1Ag-1is13Fg-1andtheNa2SO4electrolyteisnotasuitableforgraphenebasedmaterialstogethighdouble-layercapacitances[34].Graphenemaybemoresuitablefornegativeelectrodematerialstoreflectitsexcellentpropertiesthanthatforconductiveagentinpositiveelectrode[35-36].What’smore,thecyclicvoltammogramscurvesofMnO2@carbonnanotubeselectrodeandMnO2@carbonblackparticleselectrodeshowasimilarelectrochemicalpropertiesinspecificcapacitance,whichisbetterinInt.J.Electrochem.Sci.,Vol.11,20166815electrodeneedsfurtherexploration.Theslopedcharge-dischargecurvesinpotentialwindow-0.2-0.8Vwereinvestigated,asshowninFig.4b,theelectrodeofMnO2nanotubeswithcarbonnanotubesshowssignificantadvantagesoverotherelectrodesatthesamecurrentdensity.Thisresultsuggeststhatcarbonnanotubeshavehighervalueinimprovingchargestoragecapability,andwecanimagethatthesesoftthinnanotubescanbeintertwinedwitheachothertoformapowerfulnetworktoprovidehighconductionwhichwasexaminedinSEMimage(Fig.2c).Additionally,itisobviousthatthereisadistinctpotentialdrop(iR-drop)atthefirstfewtimesofdischargeprocess,whichindicatedthatthecarbonnanotubesownedthelowestresistancefromthesmallestiR-dropamongthethreekindsofconductiveadditives.Forcomparison,theNyquistplotsofMnO2nanotubeswithdifferentadditiveshavebeenincludedinFig.4c.Electrochemicalimpedancespectroscopy(EIS)spectraareoftenusedtodescribetheelectrochemicalpropertiesofsupercapacitor,suchasiontransferandelectricalconductivity.Thesemicircleathigh-to-mediumfrequenciescharacterizedthecharge-transferandtheslopeoftheinclinedlineatlowfrequencyrepresentsthediffusionresistance.Ortobemoreprecise,thestartingpointinthelineathighfrequencyrepresentthesumimpedanceoftheionicresistanceofelectrolyte,electrodes,andthecontactresistancebetweenelectrodesandcurrentcollector,whichmarkedwithRsintheequivalentcircuit.Thediameterofthesemicirclesatthemediumfrequencyindicatestheinterfacialchargetransferresistance,andRctusedtoexpresstheresistanceintheequivalentcircuit.Theslopeofthelineatthelow-frequencyreferstodiffusiveresistanceoftheelectrolyteandmarkedwithZw(Warburgimpedance)[8].ItisobviousthattheMnO2@carbonnanotubeselectrodesshowedamuchsmallerchargetransferresistance(Rct)comparedtootherelectrodes,andtheinternalresistancesofthreedifferentelectrodesextremelyclose,whichsuggestthattheconductivitiesofthreeconductiveadditivesareallexcellent.While,thelowercharge-transferresistanceofMnO2@carbonnanotubeselectrodeasmeasuredthesemicircleathigh-to-mediumfrequenciesmayduetothatcarbonnanotubeshasaone-dimensionalmultiaperturestructurewhichcomesintoafibrousnetworkandbuildsanexpresswayforcharge-transfertoimprovetheelectricalconductivityandchemicalstability.AndfromthenumericalsimulationbyDalmasalsodemonstratethecomparisonofpercolationthresholdbetweencarbonnanotubesandcarbonblackparticles[37].Theelectronicconductivityofthreekindsoftheseconductiveagentsareinturncarbonnanotubes>carbonblackparticles>graphene,whichisconformswiththeaboveanalysis.What’smore,thespecificcapacitanceoftheelectrodescanbecalculatedfromtheGCVcurvesusingthefollowingequation:Cm=It/ΔVm(1)WhereCmdenotethespecicificcapacitance(Fg-1),tisthedischargetime(s),mistheweightofactivematerials(g),IandΔVarethecurrentdensity(A)andpotentialrange(V)duringtheprocessofcharge-discharge.ThespecificcapacitanceofMnO2@carbonnanotubeselectrodereaches244.8Fg-1atcurrentdensityof1Ag-1,andthespecificcapacitancesofelectrodesMnO2@carbonblackparticlesandMnO2@grapheneare190.2Fg-1and114.1Fg-1respectively.Inaddition,thespecificcapacitanceofMnO2@carbonnanotubeselectrodestillremainsitshighestqualityreachat178.5Fg-1evenwhenthecurrentdensityisincreasedto5Ag-1,andtheMnO2@carbonblackparticleselectrodeInt.J.Electrochem.Sci.,Vol.11,20166816decreaseto132.5Fg-1,MnO2@graphene,18Fg-1respectively.Takentogether,MnO2@carbonnanotubeselectrodeisoptimalintheseelectrodes.(a)(b)Figure5.(a)CyclicvoltammogramsofMnO2@carbonnanotubeselectrodesatdifferentscanrate(5,10,2050and100mVs-1)ina1MNa2SO4aqueouselectrolyte;(b)Charge-dischargecurvesatdifferentcurrentdensities(0.5,1,2,5and10Ag-1).Concretely,thecurveofMnO2nanotubeswithcarbonnanotubesshowsarelativelygoodcapacitivebehaviorastheconductiveagent.AndtheelectrochemicalperformanceoftheMnO2@carbonnanotubeselectrodeisinvestigatedinathree-electrodeconfiguration.Fig.5ashowstheCVcurvesofMnO2@carbonnanotubeselectrodeatvariousscanratesfrom5to100mVs-1withavoltagewindowof-0.2V-0.8V.TheshapeofthecurvesoutlineshownosignificantredoxpeakssuggestsidealcapacitivebehaviorofMnO2@carbonnanotubeselectrode.Moreover,thecurrentresponsewouldgraduallyincreasewiththeincreasedscanrates,whichcausedbythereasonthatthereisnoenoughtimeathighscanratetomakeionstransferaroundthecircuit.Butallthecurvesareverysimilarandshowaquasi-rectangularshapeasthescanrateincreasesto100mVs-1,revealingtheelectrodehadanidealpseudocapacitivebehaviorwithamuchenhancedhighratecapabilityanditsfavorablechargeanddischargecharacteristicisfurthersupportedbythesymmetrictriangularshapeofgalvanostaticcharge/dischargeprofilesasshowinFig.5b.Itiswellknownthattheohmicpolarizationislinearwithcurrent,whichnotonlyimpactthecapacitancebutalsodecreasesthedischargetimeascurrentincreases.ThegoodsymmetryoftheGCDcurvesvalidatesitsefficientcapacitivebehavior,whichindicatedthatthecarbonnanotubeshadsubstantiallyimprovedthecapacitanceandcharge-dischargerateofMnO2nanotubesunderallthecurrentdensities.Anyway,thecombinationoftheMnO2nanotubesandcarbonnanotubesnotonlyincreasedconductivityandelectrolyteaccessibility,butalsoprovidedhighsurfaceareaandexcellentmechanicalproperties.Currently,theindustrialproductionisquitequalifiedforthemassproductionofcarbonnanotubesandguaranteestheperformacnce.Inallfairness,thecarbonnanotubescanbeabetterchoiceashigh-powerapplicationsataroundthesamepricewhencomparedwithotherconductiveadditives.Int.J.Electrochem.Sci.,Vol.11,20164.CONCLUSIONS6817Insummary,wehavedemonstratedacomparisonbetweendifferentconductiveadditivestoimpacttheelectrochemicalpropertiesofMnO2nanotubes.Theelectrochemicalperformancesoftheseelectrodeswereinvestigatedbyathree-electrodesystem,andtheworkingelectrodeswerepreparedbyasimplephysicalprocedureofMnO2nanotubes,conductiveadditivesandNMPwiththeproportionof7:2:1.ThenanocompositeselectrodesinourworkallrevealedexcellentpseudocapacitanceperformanceduetotheelectrochemicalpropertiesofMnO2nanotubes.Furthermore,thespecificconductivityofMnO2@carbonblackelectrode,MnO2@carbonnanotubes,MnO2@grapheneelectrodesatthecurrentdensity1Ag-1is244.8Fg-1,190.2Fg-1,and114.1Fg-1respectively.TheMnO2@carbonnanotubeselectrodeshowednotonlyimprovestheelectricalconductivityoftheMnO2@carbonblackparticlesandMnO2@grapheneelectrode,butalsoextendsthedischargetime.ThemaximumspecificcapacitanceforMnO2@carbonnanotubeselectrodereaches297.5Fg-1atthecurrentdensity0.5Ag-1andstillremainsat178.5Fg-1(60%retention)evenwhenthecurrentdensityincreasedto5Ag-1,whichcanbeputdowntothesesoftthinnanotubescanbeintertwinedwitheachothertoformapowerfulnetworktoprovideconduction.Thehighspecificcapacitanceandexcellentcharge-dischargerateoftheMnO2@carbonnanotubeselectrodeensuresitspotentialfortheapplicationsinsupercapacitorsandothermicroelectronics.ACKNOWLEDGEMENTTheauthorsgratefullyacknowledgethefinancialsupportsprovidedbyStateEducationMinistryandFundamentalResearchFundsfortheCentralUniversities(ChongqingUniversity).References1.Z.M.Hu,X.Xiao,C.Chen,T.Q.Li,L.Huang,C.F.Zhang,J.Su,L.Miao,J.J.Jiang,Y.R.Zhang,J.Zhou,NanoEnergy,11(2015)226.2.X.S.Hu,L.Johannesson,N.Murgovski,B.Egardt,AppliedEnergy,137(2015)913.3.Y.F.Tang,T.Chen,S.X.Yu,Y.Q.Qiao,S.C.Mu,S.H.Zhang,Y.F.Zhao,L.Hou,W.W.Huang,F.Gao,JournalofPowerSources,295(2015)314.4.H.L.Li,L.X.Jiang,Q.L.Cheng,Y.He,V.Pavlinek,P.Saha,C.Z.Li,ElectrochimicaActa,164(2015)252.5.Y.Tian,Z.Y.Liu,R.Xue,L.P.Huang,JournalofAlloysandCompounds,671(2016)312.6.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