B相TiO2

PreparationandelectrochemicalcapacitancebehaviorofTiO2-BnanotubesforhybridsupercapacitorG.Wanga,b,⁎,Z.Y.Liub,J.N.Wua,Q.LuaaSchoolofChemistryandChemicalEngineering,ShiheziUniversity,Xinjiang832003,ChinabKeyLaboratoryforGreenProcessingofChemicalEngineeringofXinjiangBingtuan,Xinjiang832003,ChinaabstractarticleinfoArticlehistory:Received9September2011Accepted8December2011Availableonline16December2011Keywords:TiO2MicrostructureCrystalgrowthSupercapacitorsEnergystorageandconversionTiO2-Bnanotubeswerefabricatedbyasimplemixedsolvothermalreactionandsubsequentheattreatmentat400°C.ItwasfoundthatthepreparedTiO2-Bnanotubesarecomposedofpolycrystallinephasewithinnerdiameterofabout8nm,outerdiameterofabout10nmandlengthofaboutseveralhundredsofnanometers.ThehybridsupercapacitorusingTiO2-Bnanotubesasthenegativeelectrodeandmultiwalledcarbonnano-tubes(MWCNTs)asthepositiveelectrodewasassembled.Thecellsdeliversanenergydensityof19.3Wh/kgatarateof10Cwhichiscompatiblewithafastcharging/dischargingdevice,intermediatebetweenelec-trochemicaldoublelayercapacitorandLi-ionbatteries.©2011ElsevierB.V.Allrightsreserved.1.IntroductionRecently,hybridsupercapacitorwhichutilizesanon-Faradaiccapacitativecathodeandanon-aqueouselectrolyte,coupledwithaFaradaiclithium-intercalationanodehasattractedincreasinginterestasthepromisingenergystoragedevices[1–4].Thedevicestoreschargebyareversibleadsorption/desorptionreactionofanionsonthesurfaceofthecathodematerial,andsimultaneouslyutilizesare-versibleinsertion/extractionreactionofthelithiumionsintheanodematerialtostorethecharge[2].Thecombinedeffectsprovideanoppor-tunitytoenhancetheenergydensityandpowercapabilityeffectively,whilemaintaininganacceptablecyclelifewithrespecttoconventionalsupercapacitors.TiO2-BisanidealhostforLiintercalationandextractionbecauseofitsopenstructure[5–7].IthasbeenreportedthatLi-insertionintoTiO2-BisgovernedbyapseudocapacitiveFaradaicprocess,whoserateisnotlimitedbysolid-statediffusionofLi+inabroadintervalofscanrates[8].Recently,one-dimensional(1D)nanostruc-turedtitaniamaterials,suchasnanotubes,nanorodsandnanowires,haveattractedsignificantattentionbecauseoftheirsize-anddimensionality-dependentphysicochemicalproperties[6,9].Titaniananotubes,withahollowstructure,haveahighspecificsurfaceareaandareofparticularsignificanceforhighratecapabilityaselectrodematerialsforelectrochemicallithiumioninsertionandextraction[10].Therefore,itisrationaltoenvisionTiO2-Bnanotubesasaninterestingalternativelithium-intercalationanodeforhybridsupercapacitor.TitaniananotubesandnanowiresmaybesynthesizedbyasimplehydrothermalreactionbetweenaconcentratedNaOHsolutionanddifferentTiO2precursors[9].Althoughthecontroloverthestructureandmorphologybyvaryingthereactiontemperatureandreactiontimehasbeenobserved,thepolarityandcoordinatingabilityofasolventstillhaveastrongeffectonthestructureandmorphologicalfeaturesoftheresultingproducts[11].Inthisstudy,TiO2-Bnanotubeswerefabricatedbyasimplemixedsolvothermalmethod.Thestruc-ture,morphologyandelectrochemicalcapacitancebehaviorofas-synthesizedTiO2-Bnanotubesareinvestigated.2.ExperimentalTiO2-Bnanotubesweresynthesizedbydispersing3gofanataseparticles(~325meshfromAldrich)ina60mLmixedsolventof10MNaOHaqueoussolutionandethylenediamine;thevolumeratioofNaOHaqueoussolutiontotheorganicreagentwas1:1.Theobtainedsuspensionsweresonicatedinanultrasonicbathfor0.5handthentransferredintoanautoclavewithaPTFEcontainerinside.Theautoclavewasmaintainedathydrothermaltemperatureof150°Cfor48h.Theresultingwhiteprecipitateswererecoveredbycentrifugationandwashedwitha0.1MHClsolutionanddeionizedwaterseveraltimesuntilthepHwas7,andfinallycalcinatedat400°Cfor2hintheair.Themorphologyandmicrostructureoftheas-synthesizedsampleswereinvestigatedwithtransmissionelectronmicroscopy(TEM,FEITecnai20)andX-raydiffractometer(XRD,RigakuD/max-2500).TheRamanspectraofthesampleweremeasuredonaSpectra-PhysicsMaterialsLetters71(2012)120–122⁎Correspondingauthorat:SchoolofChemistryandChemicalEngineering,ShiheziUniversity,Xinjiang832003,China.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](G.Wang).0167-577X/$–seefrontmatter©2011ElsevierB.V.Allrightsreserved.doi:10.1016/j.matlet.2011.12.036ContentslistsavailableatSciVerseScienceDirectMaterialsLettersjournalhomepage:–Nelaser(633nm).Brunauer–Emmett–Teller(BET)measurementwascarriedoutusingaNOVA2000e(Quantachrome)instrument.Electrochemicalmeasurementswerecarriedoutusingtwo-electrodecellssystemwithTiO2-Bnanotubesasthenegativeelec-trodeandmultiwalledcarbonnanotubes(MWCNTs)asthepositiveelectrode.Thecathodeandanodepelletswerefabricatedinthesameway,bypressingamixtureof80wt.%activematerials,10wt.%acetyleneblack,and10wt.%polytetrafluoroethylene(PTFE)ontoapieceofaluminumfoil.Pelletsofthesamemass(5mg)wereselectedandthenassembledassupercapacitorsinanAr-filledglove-box.Theelectrolytesolutionwas1MLiPF6dissolvedinamix-tureofethylenecarbonate(EC),dimethylcarbonate(DMC),anddiethylcarbonate(DEC),inavolumeratioofEC/DMC/DEC=1:1:1.Cyc