Article先進繊維技術科学に関する研究報告 平成11年度成果報告 6: 17-19(2000)research repor

Indrajit,  Mukhopadhyay

KawaSaki,  S.

Okino,  F.

Touhara,  H.

English

Shinshu University Institutional Repository

ELECTROCHEMICAL PROPERTIES OF MUIJTIWALL CARBONNANOTUBE Shdrajit Mukhopadhyay, S. KawaSaki, F. Okino and H. TouharaDept. of (泡eLZ7L'stTB Faculty oE 7ktl'1e Scl. &鞄cLBOloBySh'B且占zL UDL'γetSl'tB Uedal386, Japan.1. INTRODUCTIONMany forms of carbon have been teStedas anode in　lithium ion battery.Multiwall carbon nanotubes (MWNTs),grown by catalytic and electric arcdecomposition of hy血ocarbons showlarge loss of i∫reversible capacity a洗erfirst charge 【1,2】. Catalytically grownMWNTs show a strong capacitivebehaviour in a certain potential rangel1]. However, single wall nanotubes(SWNTs), grown by laser ablation, showvery high reversible capacity 【3】. Butthe reason behind such high reversiblecapacity iS not fully understood,Studies of Martin et.al, revealed thathighly ordered carbon nanotubulesshow very strong reversibleintercalation/deintercalation of Li+ andmay be suitable as anode in lithium ionbattery 【41.1m the present investigation, We reporton the electrocllemical behaviour ofMWNTs, synthesized by chemicalvapour deposition　(CVD)　usingnanopore alumina template,　toelucidate its suitability as anode in Libattery by cyclic voltammetry (CV).2.EXPERIMENTALMWNTs were synthesized by CVD ofpropylene gas using alumina nanoporetemplate at 800℃ using N2 aS Carriergas. CV was performed using glasscell with three electrode configuration,The working electrode was MWNTs(embedded in A1203)　ohmicallyconnected to Cu wire by conducting Agpaste.　Tbe Ag coIltaCt point wasinsulated by teflon paint which wasinert to both the electrolyte and thesolvent, Lithium foil connected to Cuwire was used as counter and referenceelectrode. 1M LiCIO′4　SOlution in 1:1volume ratio of EC (ethylene carbonate)and DEC (diethyl carbonate) mixedsolvent was used as electrolyte. Agcontact to the WE and ensemble ofelectrodes in the glass cell wasperformed in Ar atmosphere using drybox. WE was dried under vacuum at120℃　for overnight. A potentiostat(model HA301, Hokuto denko Ltd.) witha function generator (HB 104, Hokutodenko Ltd.) was used fわr carrying outCV experiments. An X and Y recorder-17-伊-35C, Riken Denshi Co. Ltd.) wasused.　All potentials are cited withrespect to Li/Li十.3. RESUIJrS AND DISCUSSIONSFig.1 Shows the CV of pristine MWNTs.The open circuit voltage is found to be2.98 V which indicate that the surfaceof the nanotues iB almost　free　fromoxygenated species 【1].0　　　　　　1　　　　　　2　　　　　　　3potential Vs. Li/Li+Fig. 1. Cyclicvoltannogarm of pristineMWNT (1gt cycle) at a SWeep rate Of0. 1mV8-1･Four major current peaks are observedin the first discharge scan. Peak A (at1.4　V) and B (at 1.26　V) can beattributed to the reduction of electrolyteand probably to the formation of 80lidelectrolyte interphase　(SEI) [5].Current peak C may be due todecomposition of solvent to gaseousethylene and lithium insertion intoavailable nanopores [5】. The dischargescan is completed with a sharp currentpeak at 0 V due to Li十ion intercalationto MWNTs.　On the reverse sweep(丘rst charging) a current plateau,starting at　0.4　V and extended toaround 1.5 V is noticed. This plateaumay be attributed to deintercalation ofLi'from various intercalated sites ofMWNTs,　occurrlng at differentrel0Xidation potentials.　Moreover,high　Overvoltage for deintercalationstep indicates presence of some kind ofattractive force which is hindering it.Effect of heat treatment of MWNTs atlOOO℃ on its electrocbemical propertyis shown in Fig.2. Current peaks Aand B have merged and become muchsharp.  In the cIlarglng scan thecurrent plateau is Still observable butthe shape is slightly different. Itindicates predominance of fewinterCalated sites than the rests.0<∃_(=qJL-ie;⊃U　_1000　　　　　　1　　　　　　　2　　　　　　　3Potential Vs. Li/Li十Fig.2. CV of heat-tmated (at lOOO℃)MWNT (let cycle) at a SWeep rate OfO.1mV8-1.Other successive scans (not showIカfurther confirms this fact.　Unlike- 18-other recently reported results, MWNTsunder our investigation don't exhibitany e le ctroche mic al c ap acitiveb e haviouで.4. CONCLUSIONSMWNTs　8ynthesized by CVD in thenanopore alumina template showinteI･Calation and deintercalationclearly but the mechanism is seems tobe complicated one. The intercalationsites of MWNTS are different withdifferent energetics. The absence ofany capacitive behaviour demandsfurther studies of these nanotubeswhich may be suitable as anode forLiion secondary batteries.5. ACKNOWLEDGEMENTThanks are due to Port T Kyota血andA. Tomita of Tohoku university for thepreparation of MWNTs. One of theauthors I.M. thanks tO JSPS forproviding him with a post docfellows hip5. REFERENCESl.　E, Frackowiak, S. Gautier, H.Gaucher, S. Bonnamy and F.Beguin, Caz･bon, 37, 61 (1999).2.　G. Maurin, Ch. Bousquet, FHenn, P. Bernier, R.Almairacand ち. Simon, Cnem. Z%ys.Lett., 312, 14 (1999).3.　B. Gao, A. Kleinhammes, X.P.Tangj C. Bower, L. Fleming, Y- 19Wu and 0. Zhou, them. Znys.Lett., 307, 153 (1999).4.　G. Cbe, ち.B. Laksllmi, E.R.Fisber and C.R. Martin,Nature, 398, 346 (1998).5.　P Novak, F. Joho, J.C. Panitzand 0. Hags, J. PuweT Sources,81182, 212 (1999).

ELECTROCHEMICAL PROPERTIES OF MUIJTIWALL CARBON NANOTUBES

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ELECTROCHEMICAL PROPERTIES OF MUIJTIWALL CARBON NANOTUBES

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