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制备3-D二氧化钌

Short communicationFacile preparation of three-dimensional porous hydrous ruthenium oxide electrode for supercapacitorsMyung-Gi Jeong a ,Kai Zhuo a ,Serhiy Cherevko a ,Woo-Jae Kim b ,Chan-Hwa Chung a ,*a School of Chemical Engineering,Sungkyunkwan University,Suwon 440-746,Republic of KoreabDepartment of Chemical and Environmental Engineering,Gachon University,Sungnam 461-701,Republic of Koreah i g h l i g h t sg r a p h i c a l a b s t r a c t<The highly porous Ru e (Cu)elec-trode was obtained by facile single-step electrodeposition within hydrogen evolution reaction.<The electrode eventually has the surface area of 207.5m 2g À1after electrochemical dealloying step.<The electrode exhibits a speci ﬁc capacitance of 809F g À1and good stability of 98%retention during3000th.a r t i c l e i n f oArticle history:Received 9October 2012Received in revised form 21November 2012Accepted 8December 2012Available online 16December 2012Keywords:Porous hydrous ruthenium oxide Dendrite structureHydrogen evolution reaction Electrochemical dealloying Pseudo-capacitora b s t r a c tA porous hydrous ruthenium oxide for supercapacitors is fabricated by electro-deposition accompanied with hydrogen-evolution reaction.This high-surface-area electrode (207.5m 2g À1)is developed by electrochemical de-alloying process of copper from as-deposited Ru e (Cu)foam (23.5m 2g À1).The three-dimensional structures with open pores and numerous dendritic morphologies produce good electro-chemical performances by providing the pathway for facile penetration of electrolytes into active elec-trode surface.The three-dimensional porous hydrous ruthenium oxide exhibits good capacitance performance of 809F g À1at 1.5A g À1,high energy density (112Wh kg À1),and excellent stability retention (w 98%)even after 3000cycles.Ó2012Elsevier B.V.All rights reserved.1.IntroductionRecently,the development of alternative energy sources has received a great deal of attention,due to the limitation of fossil fuels and growing environmental concerns.There are several energy conversion/storage systems which can be used as alternative energy sources [1].Among them,electrochemical capacitors (ECs)have a high power density,long cycle life,excellent reversibility,wide electrochemical window,and large speci ﬁc capacitance.Generally,supercapacitors can be divided into electric double layer capacitors (EDLCs)and pseudo-capacitors according to the material and charge e discharge mechanism.To increase the capacity and power characteristics of EDLCs,a higher speci ﬁc surface-area elec-trode needs to be used,such as activated carbon,carbon nanotubes,and carbon ﬁbers as the carbon based materials [2].On the other hand,pseudocapacitors showing faradaic reactions at the surface of the electro-active materials have mainly used transition-metal oxides and conductive polymers.Hydrous ruthe-nium oxide is known to be a promising material with the high performance characteristics required for pseudo-capacitors.The*Corresponding author.Tel.:þ82312907260;fax:þ82312907272.E-mail address:chchung@ (C.-H.Chung).Contents lists available at SciVerse ScienceDirectJournal of Power Sourcesjournal ho mep age:www.elsevi /locate/jpowsour0378-7753/$e see front matter Ó2012Elsevier B.V.All rights reserved./10.1016/j.jpowsour.2012.12.037Journal of Power Sources 244(2013)806e 811hydrous ruthenium oxide is reported to present a high speciﬁc capacitance,due to its fast and reversible proton intercalation in its lattice according to the following reaction[3]:RuO2þd Hþþd eÀ4RuO2Àd(OH)d,0d2The electro-deposition for effective preparation of hydrous ruthenium oxide electrode have been considered as a facile process, cost effectiveness,and easiness of structural change compared with various other methods such as a sol e gel method and a hydro-thermal process.The hydrous ruthenium oxide,electrochemically deposited from RuCl3$xH2O,shows the speciﬁc capacitance in the range between552F gÀ1and788F gÀ1in the literature[4e8].For economic reasons,besides,the various competent structures such as nanowires[9],nanotubes[10,11],nanoﬁbers[12],and compos-ites with carbon based materials[13,14]have been extensively researched to increase the efﬁciency of the surface reactions and reduce the ruthenium loading.In this work,we introduce the facile electrochemical deposition involving dynamic hydrogen-evolution reaction at a high cathodic overpotential,which leads to produce the higher surface area and the smaller metal loading[15e18].In our previous work,we re-ported on the preparation and the electrocatalytic performance of metallic electrodes,such as copper[19],silver[20,21],palladium [22,23],platinum[24],lead[25]and gold[26,27]which have been produced by this fabrication process.The obtained three-dimensional(3D)porous metal foams are known to enable the protons and electrons to be easily transported by providing path-ways between the electrode and electrolytes for the sake of enhancing the pseudo-capacitance[28].In fact,the ruthenium itself is difﬁcult to be made into such a3D porous structure with high surface-area dendritic morphology,due to the low exchange current density in its reduction reaction[26].In our work,we incorporate copper into ruthenium in order to facilitate the formation of dendritic structures.After the deposition,the incorporated copper has been removed with a simple electrochemical dealloying step, which results in drastic increase of speciﬁc surface area.Conse-quently,we have fabricated the porous hydrous ruthenium oxide electrodes and evaluated its characteristic as a pseudo-capacitor.2.Experimental2.1.Preparation of porous Ru e(Cu)foamRuthenium(III)chloride hydrate,Copper(II)sulfate pentahydrate (ACS reagent,!98.0%),Tin(II)chloride dihydrate(reagent grade, 98%)were purchased from Sigma e Aldrich.The sulfuric acid for supporting an electrolyte and measurement ofelectrochemicalFig.1.FESEM images of(a)top surface and(b)cross-section of a porous Ru e Cu electrode,which contain(c)dendritic and/or(d)nano-porous blossomed morphologies as deposited,and(e),(f)the surface morphologies after Cu dealloying electrochemically in H2SO4solution.M.-G.Jeong et al./Journal of Power Sources244(2013)806e811807performances were used as received from Reagents Duksan.The porous Ru e Cu foams were obtained by electro-deposition accom-panied with hydrogen-evolution reaction at high cathodic over-potentials.A three-electrode cell was installed for the deposition of3D porous Ru e Cu foams,which is utilized with a Pt/Ti on Si wafer (0.1256cm2)as a working electrode,Ag/AgCl(3M NaCl)as a refer-ence electrode,and a platinum electrode(1Â4cm2)as a counter electrode[20].The hydrogen-evolution occurs during the poten-tiostatic electro-deposition atÀ4V for5min in an aqueous elec-trolyte containing RuCl3$xH2O,CuSO4$5H2O,and H2SO4.The Copper in as-obtained porous Ru e Cu foam was then eliminated by the electrochemical de-alloying step at0.5V anodic potential with1M H2SO4solution.To describe the metal oxide layer for pseudo-capacitance behavior,the de-alloyed porous Ru e(Cu)foam was annealed in air at200 C for10h.2.2.CharacterizationThe measurement on electrochemical performance was carried out by using an electrochemical workstation(ZahnerÒElektric IM6ex,Germany).The morphologies of Ru e Cu alloy and Cu-dealloyed Ru e(Cu)foams were analyzed by scanning electron microscope(SEM),JEOL JSM-7000F(Japan)and transmission elec-tron microscopy(TEM),JEOL JEM-2100F(Japan).The X-ray diffrac-tometry(XRD)(Bruker AXS D8Discover,Germany)with Cu K a radiation at40kV and40mA has been used to evaluate the elec-trode structures.The surface area has been also measured with the ASAP2020Ò(Accelerated Surface Area and Porosimetry analyzer, U.S.A)using Brunauer e Emmett e Teller(BET)and Barrett e Joyner e Halenda(BJH)methods.3.Results and discussionFig.1(a)and(b)show the top-surface and cross-sectional images of the obtained Ru e Cu after the deposition process, respectively.In our deposition conditions,the hydrogen bubbles generated on the conductive substrate(Pt layer on Si wafer)grow to a certain size before being detached from the surface.The detached hydrogen bubbles are coalesced and gradually formed to the micron-sized pores after their evolution as shown in Fig.1(a)and (b).We found that the dendritic morphology of porous Ru e Cu was changed depending on the compositions of the aqueous solution. As the concentration of copper ions in an electrolyte(0.01M RuCl3$xH2O,0.03M CuSO4$5H2O,and1M H2SO4)was increased, the morphology of the Ru e Cu became much similar to that of the unique copper dendrite structure(cf.Fig.1(c)).In contrast,Fig.1(d) shows that the morphology of Ru e Cu,prepared in an electrolyte of higher ruthenium concentration(0.03M RuCl3$xH2O,0.01M CuSO4$5H2O,and1M H2SO4),looks like bundles of nano-porous blossoms.These nanoporous and dendritic structures possibly inﬂuence the facile pathways of ions for reactant transport during the fast charge e discharge reaction.These3D nano-pores also results in improving the energy and power density of super-capacitor,due to the uncomplicated penetration of the electrolyte into the electrode interface.Copper is not suitable for supporting the capacitance of the ruthenium oxide electrode in the present case.Consequently, copper in the3D porous Ru e Cu was eliminated by electrochemical dealloying process at0.5V anodic potential in1M H2SO4.Fig.1(e) and(f)show the morphologies of Ru e(Cu)electrodes after de-alloying step,which have numerous nano-pores.Among the other metals alloying with ruthenium,the copper is much liable to be de-alloyed maintaining its original3D structure well,whereas the tin is not suitable as shown in Fig.S1.Base on the mechanism of electro-deposition accompanied with hydrogen-evolution reaction,the increase of hydrogen-bubble evolution rate is induced when the applied current density,the process temperature,and the Hþion concentration in an electrolyte are increased.Fig.2shows the morphology change in porous Ru e Cu foam depending on the concentration of Hþions in an electrolyte. The total size of dendritic structure was decreased by increase of sulfuric acid concentration(cf.Fig.2(a)and(b)).These phenomena can be explained that the vigorous hydrogen evolution reaction leads to a rapid change of hydrodynamic conditions and mass transfer limitation by decreasing of metal ion concentration and surface energy near surface of growing metal,which inﬂuences on the growth of dendritic morphologies.In addition,the increased amount of hydrogen bubbles causes the decrease of deposited area between hydrogen bubbles during the electro-deposition process. The resulted3D porous Ru e(Cu)co-exists with dendrites and bundles of nano-porous blossom morphologies condignly exhibited the highest capacitive behaviors which was obtained with the electrolyte containing0.02M RuCl3$xH2O,0.01M CuSO4$5H2O,and 1M H2SO4(cf.Fig.2(a)).Fig.3shows the HRTEM images of the porous Ru e(Cu)elec-trodes after each process step,which reveals a dramatic increase in surface area on the dendritic electrode by dealloying process.The numerous nano-pores with a size of2e3nm are evident as shown in Fig.3(d),which possibly corresponds to vacant sites of copper removed by de-alloying(also shown in Fig.S2).As a result of thede-Fig.2.FESEM images of(a)de-alloyed Ru e(Cu)electrode,which exhibits the highest electrochemical performances,and(b)the dendritic morphology obtained after increasing Hþion concentration in the electrolyte.M.-G.Jeong et al./Journal of Power Sources244(2013)806e811 808alloying process,the BET (Brunauer e Emmett e Teller)surface area was increased from 23.5m 2g À1(as-deposited Ru e Cu)to 207.5m 2g À1.The BET surface-area and BJH pore sizes distribution of de-alloyed porous Ru e (Cu)electrode was carried out by N 2adsorption e desorption (cf .Fig.S3).Subsequently,oxidation on the porous Ru e (Cu)electrode has been done by thermal oxidation with annealing in air.According to Zheng et al.[3],the hydrous ruthenium oxide fabricated by annealing process also exhibits better electron and proton conductivity as well as superior electrochemical reversibility.Varying the annealing temperatures between 150and 500 C,we found that the optimum annealing temperature for porous Ru e (Cu)was 200 C in this work.As shown in Fig.4(d),the electrode oxidized at 200 C presents best capacitive characteristics in terms ofhigherFig.3.HRTEM images of (a)Ru e Cu as deposited and (b),(c)de-alloyed Ru in which (d)the numerous 2e 3nm sized pores are evident.M.-G.Jeong et al./Journal of Power Sources 244(2013)806e 81180910h.The best annealing condition was veriﬁed through(d)CV curves with different annealing temperatures.Fig.5.The electrochemical performances of the porous Ru e(Cu)electrode evaluated by(a)the CV curves of oxidized porous Ru e(Cu)at various scan rates(5e100mV sÀ1)from0to 1V in1M H2SO4electrolyte,(b)the speciﬁc capacitance with different scan rates(mV sÀ1),(c)the charge e discharge curves with different current densities,and(d)the retentionproperties of capacitance during3000cycles.speciﬁc capacitance and stable cyclic performance.The electro-chemical impedance spectra also reveal that there is drastic improvement in charge transfer resistance after the annealing at 200 C(cf.Fig.S5).The porous Ru e(Cu)electrodes were characterized with XRD in the2q range between25and60.The XRD patterns of the ruthenium oxide annealed at200 C in air for10h exhibit at28.5 (110), 35.5 (101),56.2 (211),and58.2 (220),as shown in Fig.4(c).The cyclic voltammograms(CV)of the porous Ru e(Cu)electrodes were obtained in the three-electrode cell with1M H2SO4electrolyte.The porous Ru e(Cu)on the Pt/Ti/Si wafer was used as a working elec-trode,and the platinum plate(1Â4cm2)and the Ag/AgCl in3M NaCl were equipped for a counter electrode and a reference elec-trode,respectively.Fig.5(a)shows the CV curves in1M H2SO4 electrolyte from0to1V at scan rates of5e100mV sÀ1.The CV curves present a rectangular shape,which is not changed signiﬁcantly with increasing scan rate.The electrode of the porous Ru e(Cu)annealed in air at200 C (the total mass of electrode:0.13mg)shows the speciﬁc capacitance of872F gÀ1at a low scan rate of5mV sÀ1and753F gÀ1at a high scan rate of100mV sÀ1.The capacitance loss is only15%even at a high scan rate,as shown in Fig.5(b).This high capacitance retention indicates that sufﬁcient ion diffusion occurred on the active sites of the porous Ru e(Cu)despite the high scan rate.Fig.5(c)shows the charge e discharge curves measured at different current densities. The cycle-life stability was also evaluated by the galvanostatic charge/discharge measurements at1.5A gÀ1,which was presented in Fig.5(d).It shows that the speciﬁc capacitance loss is only about 2%even after3000cycles.This long-term electrochemical stability indicates that the morphology of the porous Ru e(Cu)electrode is maintained during repetitive charge e discharge cycles.The speciﬁc capacitance can be calculated from Eq.(1)as follows[29,30]:Cs¼I,D t=m,D V(1) where Cs is the speciﬁc capacitance,I(A)is the discharge current applied for D t(s),and D V is the window potential in the discharge progress.The speciﬁc capacitance of the porous Ru e(Cu)is measured to be809F gÀ1at1.5A gÀ1.4.ConclusionsThe highly porous Ru e(Cu)electrode was fabricated using the electrodeposition accompanied by hydrogen evolution reaction. The electrode has a morphology consisting of nano-dendrites and nano-pores which allow a high characteristic performance as a supercapacitor(i.e.pseudo-capacitor),due to the extremely high surface area after dealloying process.The speciﬁc capacitance of the porous hydrous ruthenium oxide electrode was about809F gÀ1at 1.5A gÀ1.The energy density and power density were112Wh kgÀ1, 750W kgÀ1,respectively.These results suggest that the Faradic reaction facilitates the transportation of protons and electrons in the porous foam of dendritic morphology.Consequently,we propose that the porous metal-oxide electrodes fabricated with the electrodeposition in dynamic hydrogen template are applicable to the industrial manufacturing processes,due to its simplicity in fabrication and its superior durability.AcknowledgmentsThis research was supported by the Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education,Science and Technology (2012-0001525).Appendix A.Supplementary dataSupplementary data related to this article can be found at http:// /10.1016/j.jpowsour.2012.12.037.References[1]X.Zhao,B.M.Sanchez,P.J.Dobson,P.S.Grant,Nanoscale3(2011)839e855.[2]Y.Zhang,H.Feng,X.Wu,L.Wang,A.Zhang,T.Xia,H.Dong,X.Li,L.Zhang,Int.J.Hydrogen Energ.34(2009)4889.[3]J.P.Zheng,T.R.Jow,J.Electrochem.Soc.142(1995)L6e L8.[4]I.-H.Kim,K.-B.Kim,Electrochem.Solid-State Lett.4(2001)A62e A64.[5] B.-O.Park,C.D.Lokhande,H.-S.Park,K.D.Jung,O.-S.Joo,J.Power Sources134(2004)148e152.[6]Y.-Z.Zheng,H.-Y.Ding,M.-L.Zhang,Thin Solid Films516(2008)7381e7385.[7]V.D.Patake,C.D.Lokhande,O.S.Joo,Appl.Surf.Sci.255(2009)4192e4196.[8] C.-C.Hu,M.-J.Liu,K.-H.Chang,J.Power Sources163(2007)1126e1131.[9]H.Lee,M.S.Cho,I.H.Kim,J.D.Nam,Y.Lee,Synthetic Met.160(2010)1055e1059.[10]R.Liu,J.Duay,ne,S.B.Lee,Phys.Chem.Chem.Phys.12(2010)4309e4316.[11] C.-C.Hu,K.-H.Chang,M.-C.Lin,Y.-T.Wu,Nano Lett.6(2006)2690e2695.[12]T.-S.Hyun,H.L.Tuller,D.-Y.Youn,H.-G.Kim,I.-D.Kim,J.Mater.Chem.20(41)(2010)8971e9262.[13]G.H.Deng,X.Xiao,J.H.Chen,X.B.Zeng,D.L.He,Y.F.Kuang,Carbon43(2005)1557e1583.[14]Z.-S.Wu,D.-W.Wang,W.Ren,J.Zhao,G.Zhou,F.Li,H.-M.Cheng,Adv.Funct.Mater.20(2010)3595e3602.[15]N.D.Nikolic,K.I.Popov,L.J.Pavlovic,M.G.Pavlovic,J.Electroanal.Chem.588(2006)88e98.[16]N.D.Nikolic,G.Brankovic,M.G.Pavlovic,K.I.Popov,J.Electroanal.Chem.621(2008)13e21.[17]Y.Li,W.-Z.Jia,Y.-Y.Song,X.-H.Xia,Chem.Mater.19(2007)5758e5764.[18]H.-C.Shin,J.Dong,M.Liu,Adv.Mater.15(2003)1610e1613.[19]S.Cherevko,C.-H.Chung,Talanta80(2010)1371e1377.[20]S.Cherevko,X.Xing,C.-H.Chung,mun.12(2010)467e470.[21]S.Cherevko,C.-H.Chung,Electrochim.Acta55(2010)6383e6390.[22]X.Xing,S.Cherevko,C.-H.Chung,Mater.Chem.Phys.126(2011)36e40.[23]S.Cherevko,N.Kulyk,C.-H.Chung,Nanoscale4(2012)103e105.[24]S.Cherevko,N.Kulyk,C.-H.Chung,Nanoscale4(2012)568e575.[25]X.Xing,S.Cherevko,C.-H.Chung,Appl.Surf.Sci.257(2011)8054e8061.[26]S.Cherevko,C.-H.Chung,mun.13(2011)16e19.[27]S.Cherevko,N.Kulyk,C.-H.Chung,Langmuir28(2012)3306e3315.[28]K.-H.Chang,C.-C.Hu,Appl.Phys.Lett.88(2006)193102.[29] B.Gao,L.Hao,Q.Fu,L.Su,C.Yuan,X.Zhang,Electrochim.Acta55(2010)3681e3686.[30]Y.-Y.Liang,H.L.Li,X.-G.Zhang,J.Power Sources173(2007)599e605.M.-G.Jeong et al./Journal of Power Sources244(2013)806e811811。

英文文献-溶胶-凝胶法制备LiFePO4改进其电化学性能

Electrochimica Acta 92 (2013) 248–256Contents lists available at SciVerse ScienceDirectElectrochimicaActaj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /e l e c t a c taGel-combustion synthesis of LiFePO 4/C composite with improved capacity retention in aerated aqueous electrolyte solutionMilica Vujkovi´c a ,Ivana Stojkovi´c a ,Nikola Cvjeti´canin a ,Slavko Mentus a ,b ,∗,1a University of Belgrade,Faculty of Physical Chemistry,P.O.Box 137,Studentski trg 12-16,11158Belgrade,Serbia bThe Serbian Academy of Sciences and Arts,Kenz Mihajlova 35,11158Belgrade,Serbiaa r t i c l ei n f oArticle history:Received 2October 2012Received in revised form 3January 2013Accepted 5January 2013Available online 11 January 2013Keywords:Aqueous rechargeable Li-ion battery Galvanostatic cycling Gel-combustion Olivine LiFePO 4LiFePeO 4/C compositea b s t r a c tThe LiFePO 4/C composite containing 13.4wt.%of carbon was synthesized by combustion of a metal salt–(glycine +malonic acid)gel,followed by an isothermal heat-treatment of combustion product at 750◦C in reducing atmosphere.By a brief test in 1M LiClO 4–propylene carbonate solution at a rate of C/10,the discharge capacity was proven to be equal to the theoretical one.In aqueous LiNO 3solu-tion equilibrated with air,at a rate C/3,initial discharge capacity of 106mAh g −1was measured,being among the highest ones observed for various Li-ion intercalation materials in aqueous solutions.In addition,signiﬁcant prolongation of cycle life was achieved,illustrated by the fact that upon 120charg-ing/discharging cycles at various rates,the capacity remained as high as 80%of initial value.The chemical diffusion coefﬁcient of lithium in this composite was measured by cyclic voltammetry.The obtained val-ues were compared to the existing literature data,and the reasons of high scatter of reported values were considered.© 2013 Elsevier Ltd. All rights reserved.1.IntroductionThanks to its high theoretical Coulombic capacity (170mAh g −1)and environmental friendliness,LiFePO 4olivine became a desir-able cathodic material of Li-ion batteries [1,2],competitive to other commercially used cathodic materials (LiMnO 4,LiCoO 2).As evidenced in non-aqueous electrolyte solutions,a small vol-ume change (6.81%)that accompanies the phase transition LiFePO 4 FePO 4enables Li +ion insertion/deinsertion reactions to be quite reversible [1–3].The problem of low rate capability,caused by low electronic conductivity [4,5],was shown to be solv-able to some extent by reduction of mean particle size [6].Further improvements in both conductivity and electrochemical perform-ances were achieved by forming composite LiFePO 4/C,where in situ produced carbon served as an electronically conducting con-stituent [5,7–27].Ordinarily,both in situ formed carbon and carbon black additive,became unavoidable constituent of the LiFePO 4-based electrode materials [28–37].Zhao et al.[27]reported that Fe 2P may arise as an undesirable product during the synthesis of LiFePO 4/C composite under reducing conditions,however,other authors found later that this compound may contribute positively∗Corresponding author at:University of Belgrade,Faculty of Physical Chemistry,P.O.Box 137,Studentski trg 12-16,11158Belgrade,Serbia.Tel.:+381112187133;fax:+381112187133.E-mail address:slavko@ffh.bg.ac.rs (S.Mentus).1ISE member.to the electronic conductivity and improve the electrochemical per-formance of the composite [28–30].Severe improvement in rate capability and capacity retention was achieved by partial replace-ment of iron by metals supervalent relative to lithium [31–37].Thus one may conclude that the main aspects of practical applica-bility of LiFePO 4in Li-ion batteries with organic electrolytes were successively resolved.After the pioneering studies by Li and Dahn [38,39],recharge-able Li-ion batteries with aqueous electrolytes (ARLB)attracted considerable attention [40–50].The ﬁrst versions of ARLB’s,suf-fered of very low Coulombic utilization and signiﬁcantly more pronounced capacity fade relative to the batteries with organic electrolyte,regardless on the type of electrode materials [43].For the ﬁrst time,LiFePO 4was considered as a cathode material in ARLB’s by Manickam et al.in 2006[44].He et al.[46],in an aqueous 0.5M Li 2SO 4solution,found that LiFePO 4displayed both a surprisingly high initial capacity of 140mAh g −1at a rate 1C and recognizable voltage plateau at a rate as high as 20C,which was superior relative to the other electrode materials in ARLB’s.Recently,the same authors reported a high capacity decay in aer-ated electrolyte solution,amounting to 37%after only 10cycles [48].In the same study,they demonstrated qualitatively by a brief cyclovoltammetric test,that a carbon layer deposited from a vapor phase over LiFePO 4particles,suppressed the capacity fade [48].Inspired by the recent discoveries about excellent rate capa-bility [46]but short cycle life [48]of LiFePO 4in aerated aqueous solution,we attempted to prolong the cycle life by means of protecting carbon layer over the LiFePO 4particles.Therefore we0013-4686/$–see front matter © 2013 Elsevier Ltd. All rights reserved./10.1016/j.electacta.2013.01.030M.Vujkovi´c et al./Electrochimica Acta92 (2013) 248–256249synthesized LiFePO4/C composite by a fast and simple glycine-nitrate gel-combustion technique.This method,although simpler than a classic solid state reaction method combined with ball milling[44,48],was rarely used for LiFePO4synthesis[19,27].It yielded a porous,foamy LiFePO4/C composite,easily accessible to the electrolyte.Upon the fair charging/discharging performance was conﬁrmed by a brief test in organic electrolyte,we examined in detail the electrochemical behavior of this material in aqueous electrolyte,by cyclic voltammetry,complex impedance and cyclic galvanostatic charging/discharging methods.In comparison to pure LiFePO4studied in Ref.[48],this composite displayed markedly longer cycle life in aerated aqueous solutions.The chemical dif-fusion coefﬁcient of lithium was also determined,and the reasons of its remarkable scatter in the existing literature were considered.2.ExperimentalThe LiFePO4/C composite was synthesized using lithium nitrate, ammonium dihydrogen phosphate(Merck)and iron(II)oxalate dihydrate(synthesized according to the procedure described else-where[51])as raw materials.Our group acquired the experience in this synthesis technique on the examples of spinels LiMn2O4 [52]and LiCr0.15Mn1.85O4[53],where glycine served as both fuel and complexing/gelling agent to the metal ions.A stoichiometric amount of each material was dissolved in deionized water and mixed at80◦C using a magnetic stirrer.Then,ﬁrst glycine was added into the reaction mixture to provide the mole ratio of glycine: nitrate of2:1,and additionally,malonic acid(Merck)was added in an amount of60wt.%of the expected mass of LiFePO4.The role of malonic acid was to decelerate combustion and provide con-trollable excess of carbon[14].After removing majority of water by evaporation,the gelled precursor was heated to initiate the auto-combustion,resulting in aﬂocculent product.The combustion product was heated in a quartz tube furnaceﬁrst at400◦C for3h in Ar stream,and then at750◦C for6h,under a stream of5vol.%H2in Ar.This treatment consolidated the olivine structure and enabled to complete the carbonization of residual organic matter.The VO2powder prepared by hydrothermal method was used as an active component of the counter electrode in the galvanostatic experiments in aqueous electrolyte solution.The details of the syn-thesis and electrochemical behavior of VO2are described elsewhere [54,55].The considerable stoichiometric excess of VO2was used,to provide that the LiFePO4/C composite only presents the main resis-tive element,i.e.,determines the behavior of the assembled cell on the whole.The XRD experiment was performed using Philips1050diffrac-tometer.The Cu K␣1,2radiation in15–70◦2Ârange,with0.05◦C step and2s exposition time was used.The carbon content in the composite was determined by its com-bustion in theﬂowing air atmosphere,by means of thermobalance TA SDT Model2090,at a heating rate of10◦C min−1.The morphology of the synthesized compounds was observed using the scanning electron microscope JSM-6610LV.For electrochemical investigations,the working electrode was made from LiFePO4/C composite(75%),carbon black-Vulcan XC72 (Cabot Corp.)(20%),poly(vinylideneﬂuoride)(PVDF)binder(5%) and a N-methyl-2-pyrrolidone solvent.The resulting suspension was homogenized in an ultrasonic bath and deposited on electron-ically conducting support.The electrode was dried at120◦C for 4h.Somewhat modiﬁed weight ratio,85:10:5,and the same drying procedure,were used to prepare VO2electrode.The non-aqueous electrolyte was1M LiClO4(Lithium Corpo-ration of America)dissolved in propylene carbonate(PC)(Fluka). Before than dissolved,LiClO4was dried over night at140◦C under vacuum.The aqueous electrolyte solution was saturated LiNO3solution.The cyclic voltammetry and complex impedance experiments were carried out only for aqueous electrolyte solutions,by means of the device Gamry PCI4/300Potentiostat/Galvanostat.The three electrode cell consisted of a working electrode,a wide platinum foil as a counter electrode,and a saturated calomel electrode(SCE) as a reference one.The experiments were carried out in air atmo-sphere.The impedance was measured in open-circuit conditions, at various stages of charging and discharging,within the frequency range10−2−105Hz,with7points per decade.Galvanostatic charging/discharging experiments were carried out in a two-electrode arrangement,by means of the battery testing device Arbin BT-2042,with two-terminal connectors only.In the galvanostatic tests in non-aqueous solution,working electrode was a2×2cm2platinum foil carrying2.3mg of compos-ite electrode material(1.5mg of olivine),while counter electrode was a2×2cm2lithium foil.The cell was assembled in an argon-ﬁlled glove box and cycled galvanostatically within a voltage range 2.1–4.2V.The galvanostatic tests in the aqueous electrolyte solution were carried out in a two-electrode arrangement,involving3mg of cathodic material,as a working electrode,and VO2in a multi-ple stoichiometric excess,as a counter electrode.According to its reversible potential of lithiation/delithiation reaction[55],VO2per-formed as an anode in this cell.The4cm2stainless steel plates were used as the current collectors for both positive and negative electrode.The cell was assembled in room atmosphere,and cycled within the voltage window between0.01and1.4V.3.Result and discussion3.1.The XRD,SEM and TG analysis of the LiFePO4/C compositeFig.1shows the XRD patterns of the composite LiFePO4/C pre-pared according to the procedure described in the Experimental Section.As visible,the diffractogram agrees completely with the one of pure LiFePO4olivine,found in the JCPDS card No.725-19. The narrow diffraction lines indicate complete crystallization and relatively large particle dimensions.On the basis of absence of diffraction lines of carbon,we may conclude that the carbonized product was amorphous one.Fig.2shows the SEM images of the LiFePO4/C composite at two different magniﬁcations.Theﬂaky agglomerates,Fig.2left,with apparently smooth surface and low tap density,are due to a partial liquefaction and evolution of gas bubbles during gel-combustion procedure.These agglomerates consist of small LiFePO4/CFig.1.XRD patterns of LiFePO4/C composite in comparison to standard crystallo-graphic data.250M.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256Fig.2.SEM images of LiFePO 4/C composite at two different magniﬁcation,20000×and 100000×.composite particles visible better at higher magniﬁcation,Fig.2,ly at the magniﬁcation of 100,000×,one may see that the size of majority of composite particles was in the range 50–100nm.The mean particle diameter,2r,as per SEM microphotograph amounted to 75nm.This analysis evidences that the gel-combustion method may provide nanodisprsed particles,desirable from the point of view of rate capability.For instance,Fey et al.[16]demonstrated that particle size reduction from 476to 205nm improved the rate capa-bility of LiFePO 4/C composite in organic electrolyte,illustrated by the increase of discharge capacity from 80mAh g −1to 140mAh g −1at discharging rate 1C.Also,carbon matrix prevented particles from agglomeration providing narrow size distribution,contrary to often used solid state reaction method of synthesis,when sintering of ini-tially nanometer sized particles caused the appearance of micron sized agglomerates [22].The SEM microphotograph (Fig.2)alone did not permit to rec-ognize carbon constituent of the LiFePO 4/C composite.However,carbonized product was evidenced,and its content measured,by means of thermogravimetry,as described elsewhere [9].The dia-gram of simultaneous thermogravimetry and differential thermal analysis (TG/DTA)of the LiFePO 4/C composite performed in air is presented in Fig.3.The process of moisture release,causing a slight mass loss of 1%,terminated at 150◦C.In the temperature range 350–500◦C carbon combustion took place,visible as a drop of the TG curve and an accompanying exothermic peak of the DTA curve.However,the early stage of olivine oxidation merged to some extent with the late stage of carbon combustion,and therefore,the minimum of the TG curve,appearing at nearly 500◦C,was not so low as to enable to read directly the carbon content.Fortunately,as proven by XRD analysis,the oxidation of LiFePO 4at tempera-ture exceeding 600◦C,yielded only Li 3Fe 2(PO 4)3and Fe 2O 3,whatFig.3.TGA/DTA curve of LiFePO 4/C under air ﬂow at heating rate of 10C min−1.corresponded to the relative gain in mass of exactly 5.07%[9].Therefore,the weight percentage of carbonaceous fraction in the LiFePO 4/C composite was determined as equal to the difference between the TG plateaus at temperatures 300and 650◦C,aug-mented for 5.07%.According to this calculation the carbon fraction amounted to 13.4wt.%,and by means of this value,the electro-chemical parameters discussed in the next sections were correlated to pure LiFePO 4.Speciﬁc surface area of LiFePO 4,required for the measurement of diffusion constant,was determined from SEM image (Fig.2).Assuming a spherical particle shape and accepting mean particle radius r =37.5nm,the speciﬁc surface area was estimated on the basis of equation [17,22,45,46]:S =3rd(1)where the bulk density d =3.6g cm −3was used .This calculation resulted in the value S =22.2m 2g −1.In this calculation the contri-bution of carbon to the mean particle radius was ignored,however the error introduced in such way is more acceptable than the error which may arise if standard BET method were applied to the com-posite with signiﬁcant carbon ly,due to a usually very developed surface area of carbon,the measured speciﬁc sur-face may exceed many times the actual surface area of LiFePO 4.3.2.Electrochemical measurements3.2.1.Non-aqueous electrolyte solutionIn order to compare the behavior of the synthesized LiFePO 4/C composite to the existing literature data,available predominantly for non-aqueous solutions,a brief test was performed in non-aqueous 1M LiClO 4+propylene carbonate solution by galvano-static experiments only.The results for the rates C/10,C/3and C,within the voltage limits 2.1–4.2V,were presented in Fig.4.The polarizability of the lithium electrode was estimated on the basis of the study by Churikov [56–67],who measured the current–voltage curves of pure lithium electrode in LiClO 4/propylene carbon-ate solutions at various temperatures.To the highest rate of 1C =170mA g −1in nonaqueous electrolyte,the corresponding cur-rent amounted to 0.25mA,which was equal to the current density of 0.064mA cm −2through the Li counter electrode.According to Fig.2in Ref.[67],for room temperature,the corresponding over-voltage amounted to only 6mV.Since lithium electrode is thus practically non-polarizable in this system,the voltages presented on the ordinate of the left diagram are the potentials of the olivine electrode expressed versus Li/Li +reference electrode.The clear charge and discharge plateaus at about 3.49V and 3.40V,respec-tively,correspond to the LiFePO 4 FePO 4phase equilibria [5].At discharging rate of C/10,the initial discharge capacity,within the limits of experimental error,was close to a full theoreticalM.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256251Fig.4.The initial charge/discharge curves (a)and cyclic performance (b)of LiFePO 4/C composite in 1M LiClO 4+PC at different rates within a common cut-off voltage of2.1–4.2V.Fig.5.Charge/discharge proﬁle and corresponding cyclic behavior of LiFePO 4/C in 1M LiClO 4+PC at the rate of 1C.capacity of LiFePO 4(170mAh g −1).This value is higher than that for LiFePO 4/C composite obtained by glycine [19],malonic acid [14]and adipic acid/ball milling [15]assisted methods.As usual,the discharge capacity decreased with increasing discharging rate (Fig.4b),and amounted to 127mAh g −1at C/3,and 109mAh g −1at 1C.For practical application of Li-ion batteries,a satisfactory rate capability and long cycle life are of primary importance.The charge/discharge proﬁles and dependence of capacity on the cycle number at the rate 1C are presented in Fig.5.The capacity was almost independent on the number of cycles,similarly to theearlier reports by Fey et al.[37–39].For comparison,Kalaiselvi et al.[19],by a glycine assisted gel-combustion procedure,with an additional amount (2wt.%)of carbon black,produced a similar nanoporous LiFePO 4/C composite displaying somewhat poorer per-formance,i.e.,smaller discharge capacity of 160mAh g −1at smaller discharging rate of C/20.On the other hand,better rate capability of LiFePO 4/C com-posite,containing only 1.1–1.8wt.%of carbon,in a non-aqueous solution,was reported by Liu et al.[21].For instance they mea-sured 160mAh g −1at the rate 1C,and 110at even 30C [21].This may be due to a thinner carbon layer around the LiFePO 4olivine particles.However the advantage of here applied thicker carbon layer exposed itself in aqueous electrolyte solutions,as described in the next section.3.2.2.Aqueous electrolyte solution3.2.2.1.Cyclic voltammetry.By the cyclic voltammetry method (CV)the electrochemical behavior of LiFePO 4/C composite in satu-rated aqueous LiNO 3solution was preliminary tested in the voltage range 0.4–1V versus SCE.The cyclic voltammograms are pre-sented in Fig.6.The highest scan rate of 100mV s −1,tolerated by this material,was much higher than the ones (0.01–5mV s −1)used in previous studies in both organic [13,24,25]and aqueous electrolyte solutions [47,48].Since one deals here with the thin layer solid redox electrode,limited in both charge consumption and diffusion length,the voltammogram is more complicated for interpretation comparing with the classic case of electroactive species in a liquid solution.A sharp,almost linear rise of current upon achieving reversible potential,with overlapped rising parts at various scan rates,similar to ones reported elsewhere [21,25],resembles closely the voltammogram of anodic dissolution ofaFig.6.Cyclic voltammograms of LiFePO 4/C in saturated LiNO 3aqueous electrolyte with a scan rate of 1mV s −1(left)and at various scan rates in the range 1–100mV s −1.252M.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256Fig.7.Anodic and cathodic peak current versus square root of scan rate forLiFePO 4/C composite in aqueous LiNO 3electrolyte solution.thin metal layer [56],which proceeds under constant reactant activity.Since the solid/solid phase transitions LiFePO 4 FePO 4accompanies the redox processes in this system [5,8,57,58],the positive scan of the voltammograms depict the phase transition of LiFePO 4to FePO 4,while the negative scan depicts the phase transi-tion FePO 4to LiFePO 4.As shown by Srinivasan et al.[5],LiFePO 4may be exhausted by Li not more than 5mol.%before to trans-form into FePO 4,while FePO 4may consume no more than 5%Li before to transform into LiFePO 4,i.e.cyclic voltammetry exper-iments proceeds under condition of almost constant activity of the electroactive species.Although these aspects of the Li inser-tion/deinsertion process do not ﬁt the processes at metal/liquid electrolyte boundary implied by Randles–Sevcik equation:i p =0.4463F RT1/2C v 1/2AD 1/2(2)this equation was frequently used to estimate apparent diffusion coefﬁcient in Li insertion processes [5,17,21,46,59].To obtain peak current,i p ,in amperes,the concentration of lithium,C =C Li ,should be in mol cm −3,the real surface area exposed to the electrolyte in cm 2,chemical diffusion coefﬁcient of lithium through the solid phase,D =D Li ,in cm 2s −1,and sweep rate,v ,in V s −1.The Eq.(2)pre-dicts the dependence of the peak height on the square root of sweep rate to be linear,as found often in Li-ion intercalation processes [17,21,25,59,60].This condition is fulﬁlled in this case too,as shown in Fig.7.The average value of C Li may be estimated as a reciprocal value of molar volume of LiFePO 4(V M =44.11cm 3mol −1),hence C Li =2.27×10−2mol cm −3.The determination of the actual surface area of olivine is a more difﬁcult task,due to the presence of carbon in the LiFePO 4/C ly,classical BET method of sur-face area measurement may lead to a signiﬁcantly overestimated value,since carbon surface may be very developed and participate predominantly in the measured value [15].Thus the authors in this ﬁeld usually calculated speciﬁc surface area by means of Eq.(1),using mean particle radius determined by means of electron microscopy [17,22,45,46].Using S =22.2m 2g −1determined by means of Eq.(1),and an actual mass of the electroactive substance applied to the elec-trode surface (0.001305g),the actual electrode surface area was calculated to amount to A =290cm 2.This value introduced in Randles–Sevcik equation yielded D Li ∼0.8×10−14cm 2s −1.From the aspect of capacity retention,the insolubility of olivine in aqueous solutions is advantageous compared to the vanadia-based Li-ion intercalation materials,such as Li 1.2V 3O 8[61],LiV 3O 8[62]and V 2O 5[63],the solubility of which in LiNO 3solution was perceivable through the yellowish solutioncoloration.Fig.8.The Nyquist plots of LiFePO 4/C composite in aqueous LiNO 3solution at var-ious stages of delithiation;inset:enlarged high-frequency region.3.2.2.2.Impedance measurements.Figs.8and 9present the Nyquist plots of the LiFePO 4/C composite in aqueous LiNO 3solution at various open circuit potentials (OCV),during delithiation (anodic sweep,Fig.8)and during lithiation (cathodic sweep,Fig.9).The delithiated phase,observed at OCV =1V,as well as the lithi-ated phase,observed at OCV =0V,in the low-frequency region (f <100Hz)tend to behave like a capacitor,characteristic of a surface thin-layered redox material with reﬂective phase bound-ary conditions [64].At the OCV not too far from the reversible one (0.42V during delithiation,0.308V during lithiation),where both LiFePO 4and FePO 4phase may be present,within the whole 10−2–105Hz frequency range,the reaction behaves as a reversible one (i.e.shows the impedance of almost purely Warburg type).The insets in Figs.8and 9present the enlarged parts of the impedance diagram in the region of high frequencies,where one may observe a semicircle,the diameter of which corresponds theoretically to the charge transfer resistance.As visible,the change of open circuit potential between 0and 1V,in spite of the phase transition,does not cause signiﬁcant change in charge transfer resistance.The small charge transfer resistance obtained with the carbon participation of 13.4%,being less than 1 ,is the smallest one reported thus far for olivine based materials.This ﬁnding agrees with the trend found by Zhao et al.[27],that the charge transfer resistance scaleddownFig.9.The Nyquist plots of LiFePO 4/C composite in aqueous LiNO 3solution at var-ious stages of lithiation;inset:enlarged high-frequency region.M.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256253Fig.10.The dependence Z Re vs.ω−1/2during lithiation at 0.308V (top)and delithi-ation at 0.42V (down)in the frequency range 72–2.68Hz.to 1000,400and 150 when the amount of in situ formed carbon in the LiFePO 4/C composite increased in the range 1,2.8and 4.8%.For OCV corresponding to the cathodic (0.42V)and anodic (0.308V)peak maxima,the Warburg constant W was calculated from the dependence [21]:Z Re =R e +R ct + W ω−1/2(3)In the frequency range 2.7–72Hz,almost purely Warburg impedance was found to hold (i.e.the slope of the Nyquist plot very close to 45degrees was found).At the potential of cathodic current maximum (0.42V),from Fig.10, W was determined to amount to 7.96 s −1/2.At the potential of anodic maxima,0.308V, W was determined to amount to 9.07 s −1/2.In the published literature,for the determination of diffusion coefﬁcient on the basis of impedance measurements,the following equation was often used [66,68,69]:D =0.5V M AF W ıE ıx2(4)where V M is molar volume of olivine,44.1cm 3, W is Warburg con-stant and ıE /ıx is the slope of the dependence of electrode potential on the molar fraction of Li (x )for given value of x .However,the potentials of CV maxima in the here studied case correspond to the x range of two-phase equilibrium,where for an accurate deter-mination of ıE /ıx a strong control of perturbed region of sample particles is required [69],and thus the determination of diffusion coefﬁcients was omitted.3.2.2.3.Galvanostatic measurements.The galvanostatic measure-ments of LiFePO 4/C in saturated LiNO 3aqueous solution were performed in a two-electrode arrangement using hydrother-mally synthesized VO 2[55]as the active material of thecounterFig.11.Capacity versus cycle number and charge/discharge proﬁles (inset)for thecell consisting of LiFePO 4/C composite as cathode,and VO 2in large excess as anode,in saturated LiNO 3aqueous electrolyte observed at rate C/3.electrode.Preliminary cyclovoltammetric tests of VO 2in saturated LiNO 3solution at the sweep rate 10mV s −1,evidenced excellent cyclability and stable capacity of about 160mAh g −1during at least 50cycles.The voltage applied to the two-electrode cell was cycled within the limits 0and 1.4V.Due to a signiﬁcant stoichiometric excess of VO 2over LiFePO 4/C composite (5:1)the actual voltage may be considered to be the potential versus reference VO 2/Li x VO 2electrode.Fig.11shows the dependence of the discharging Coulombic capacity of the LiFePO 4/C composite on the number of galvano-static cycles at discharging rate C/3,as well as (in the inset)the voltage vs.charging/discharging degree for 1st,2nd and 50th cycle.The charge/discharge curves do not change substantially in shape upon cycling,indicating stable capacity.For an aqueous solution,a surprisingly high initial discharge capacity of 106mAh g −1and low capacity fade of only 6%after 50charge/discharge cycles were evidenced.This behavior is admirable in comparison to other elec-trode materials in aqueous media reported in literature (LiTi 2(PO 4)3[42],LiV 3O 8[57]),and probably enabled by a higher thermody-namic stability of olivine structure [1].Fig.12presents the results of cyclic galvanostatic investigations of LiFePO 4/C composite in aqueous LiNO 3solution at various dis-charging rates.The charging/discharging rate was initially C/3for 80cycles and then was increased stepwise up to 3C.ThecapacityFig.12.Cyclic performance of LiFePO 4/C in saturated LiNO 3aqueous electrolyte at different charging/discharging rates.。

Supercapacitor

SupercapacitorSupercapacitors (SC),[1]comprise a family of electrochemical capacitors. Supercapacitors, sometimes called ultracapacitors or electric double-layer capacitor (EDLC), don't have a conventional solid dielectric. The capacitance value of an electrochemical capacitor is determined by the combination of two storage effects:[2][3][4]∙Double-layer capacitance–electrostatic storage of the electrical energyachieved by separation of charge in a Helmholtz double layer at the interfacebetween the surface of a conductive electrode and a electrolyte. The separation of charge distance in a SC is on the order of a few Angstroms (0.3–0.8 nm) and is static.[5]∙Pseudocapacitance–Electrochemical storage of the electrical energy, achieved by redox reactions with specifically adsorbed ions from the electrolyte, intercalation of atoms in the layer lattice or electro-sorption, underpotential deposition of hydrogen or metal adatoms in surface lattice sites which result in a reversible faradaic charge-transfer.[5]The ratio of the storage resulting from each principle can vary greatly, depending on electrode design and electrolyte composition. Pseudo-capacitance can increase the capacitance value by as much as an order of magnitude over that of the double-layer by itself.[1]Supercapacitors are divided into three families, based on the design of the electrodes: ∙Double-layer capacitors –with carbon electrodes or derivates with muchhigher static double-layer capacitance than the faradaic pseudocapacitance ∙Pseudocapacitors –with electrodes out of metal oxides or conducting polymers with a high amount of faradaic pseudocapacitance∙Hybrid capacitors – capacitors with special electrodes that exhibit significant capacitance from both principlesHierarchical classification of supercapacitors and related typesSupercapacitors occupy the gap between traditional capacitors and rechargeable batteries. They have higher capacitance values per unit volume and greater energy density than other capacitors. They support up to 12 Farads/1.2 Volt, with capacitance values up to 10 times that of electrolytic capacitors.[1] While existing supercapacitors have energy densities that are approximately 10% of a conventional battery, their power density is generally 10 to 100 times greater. Power density is defined as the product of energy density, multiplied by the speed at which the energy is delivered to the load. The greater power density results in much shorter charge/discharge cycles than a battery is capable, and a greater tolerance for numerous charge/discharge cycles.Within electrochemical capacitors, the electrolyte is the conductive connection between the two electrodes, distinguishing them from electrolytic capacitors, in which the electrolyte is the cathode and second electrode.Supercapacitors are polarized and must operate with correct polarity. Polarity is controlled by design with asymmetric electrodes, or, for symmetric electrodes, by a potential applied during the manufacturing process.Supercapacitors support a broad spectrum of applications for power and energy requirements, including:[6]∙Long duration, low current, for memory backup in (SRAMs)∙Power electronics that require very short, high current, as in the KERSsystem in Formula 1 cars∙Recovery of braking energy for vehiclesHistoryDevelopment of electrochemical capacitorsIn the early 1950s, General Electric engineers began experimenting with devices using porous carbon electrodes for fuel cells and rechargeable batteries. Activated charcoal is an electrical conductor that is extremely porous carbon with a high specific surface area, providing a useful electrode material. In 1957 H. Becker developed a "Low voltage electrolytic capacitor with porous carbon electrodes".[7][8][9] He believed that the energy was stored as a charge in the carbon pores as in the etched foils of electrolytic capacitors. Because the double layer mechanism was not known at the time, he wrote in the patent: "It is not known exactly what is taking place in the component if it is used for energy storage, but it leads to an extremely high capacity." General Electric did not immediately pursue this work.In 1966 researchers at Standard Oil of Ohio (SOHIO) developed another version of the devices as ―Electrical energy storage apparatus‖, while working on experimental fuel cell designs.[10][11]The nature of electrochemical energy storage was not described in this patent. Even in 1970, the electrochemical capacitor patented by Donald L. Boos was registered as an electrolytic capacitor with activated carbon electrodes.[12]Principle construction of a supercapacitor; 1. power source, 2. collector, 3.polarized electrode, 4. Helmholtz double layer, 5. electrolyte having positive and negative ions, 6. Separator. By applying a voltage to the capacitor at both electrodes a respective Helmholtz double layer is formed, which has a positive or negative layer of ions from the electrolyte deposited in a mirror image on the respective opposite electrode.These early electrochemical capacitors used a cell design of two aluminum foils covered with activated carbon - the electrodes - which were soaked in an electrolyte and separated by a thin porous insulator. This design gave a capacitor with a capacitance value in the one "farad" area, which was significantly higher than for electrolytic capacitors of the same dimensions. This basic mechanical design remains the basis of most electrochemical capacitors.SOHIO did not commercialize their invention, licensing the technology to NEC, who finally marketed the results as ―supercapacitors‖ in 1971, to provide backup power for computer memory.[11] Other manufacturers followed from the end of the 1970s. Around 1978 Panasonic marketed its "Goldcaps‖ brand.[13]This product became a successful back-up energy source for memory backup applications.[11]The competition started some years later. In 1987 ELNA"Dynacap"s entered the market.[14] This generation had relatively high internal resistance, which limited the discharge current. They were used for low current applications like powering SRAM chips or for data backup.At the end of the 1980s improved electrode materials led to higher capacitance values and in lower resistance electrolytes that lowered the ESR in order to increase the charge/discharge currents. This led to rapidly improving performance and a rapid reduction in cost.The first supercapacitor with low internal resistance was developed in 1982 for military applications through the Pinnacle Research Institute(PRI), and were marketed under the brand name "PRI Ultracapacitor". In 1992, Maxwell Laboratories, later Maxwell Technologies took over this development. Maxwell adopted the term Ultracapacitor from PRI and called them "Boost Caps"[5]to underline their use for power applications.Since the energy content of a capacitor increases with the square of the voltage, researchers were looking for a way to increase the breakdown voltage. Using an anode of a 200V high voltage tantalum electrolytic capacitor in 1994 David A. Evans developed an "Electrolytic-Hybrid Electrochemical Capacitor".[15][16]These capacitors combine features of electrolytic and electrochemical capacitors. They combine the high dielectric strength of an anode from an electrolytic capacitor, and the high capacitance with a pseudocapacitive metal oxide (ruthenium (IV) oxide) cathode from an electrochemical capacitor, yielding a hybrid. Evans' Capattery[17] had an energy content about a factor of 5 higher than a comparable tantalum electrolytic capacitor of the same size.[18]Their high costs limited them to specific military applications.Recent developments in lithium-ion capacitors are also hybrids. They were pioneered by FDK in 2007.[19]They combine an electrostatic double-layer electrode with a doped lithium-ion electrochemical battery electrode to generate high pseudocapacitance additional to high double-layer capacitance.Development of the double layer and pseudocapacitance model HelmholtzWhen a metal (or an electronic conductor) is brought in contact with a solid or liquid ionic-conductor (electrolyte), a common boundary (interface) among the two different phases emerges. Helmholtz[20]was the first to realize that charged electrodes immersed in electrolytic solutions repel the coions of the charge while attracting counterions to their surfaces. With the two layers of opposite polarity formed at the interface between electrode and electrolyte in 1853 he showed that an electrical double layer (DL) that is essentially a moleculear dielectric achieved electrostatic charge storage.[21] Below the electrolyte's decomposition voltage the stored charge is linearly dependent on the voltage applied.This early Helmholtz model predicted a constant differential capacitance independent from the charge density depending on the dielectric constant of the solvent and the thickness of the double-layer.[5][22][23] But this model, while a good foundation, does not consider important factors including diffusion/mixing of ions in solution, the possibility of adsorption onto the surface and the interaction between solvent dipole moments and the electrode.Simplyfied illustration of the potential development in the area and in the further course of a Helmholtz double layer.Gouy\Chapman [edit]Louis Georges Gouy in 1910 and David Leonard Chapman in 1913 both observed that capacitance was not a constant and that it depended on the applied potential and the ionic concentration. The ―Gouy-Chapman model‖ made significant improvements by introducing a diffuse model of the DL. In this model the charge distribution of ions as a function of distance from the metal surface allows Maxwell–Boltzmann statistics to be applied. Thus the electric potential decreases exponentially away from the surface of the fluid bulk.[5][24]Stern [edit]Gouy-Chapman fails for highly charged DLs. In order to resolve this problem Otto Stern in 1924 suggested the combination of the Helmholtz and Gouy-Chapman models. In Stern's model, some of the ions adhere to the electrode as suggested by Helmholtz, giving an internal Stern layer and some form a Gouy-Chapman diffuse layer.[25]The Stern layer accounted for ions' finite size and consequently ions have a closest approach to the electrode on the order of the ionic radius. The Stern model too had limitations, effectively modeling ions as point charges, assuming all significant interactions in the diffuse layer are Coulombic, assuming dielectric permittivity to beconstant throughout the double layer, and that fluid viscosity is constant above the slipping plane.[26]Grahame [edit]Thus, D. C. Grahame modified Stern in 1947.[27]He proposed that some ionic or uncharged species can penetrate the Stern layer, although the closest approach to the electrode is normally occupied by solvent molecules. This could occur if ions lost their solvation shell when the ion approached the electrode. Ions in direct contact with the electrode were called ―specifically adsorbed ions‖. This model proposed the existence of three regions. The inner Helmholtz plane (IHP) plane passing through the centres of the specifically adsorbed ions. The outer Helmholtz plane (OHP) passes through the centres of solvated ions at their distance of closest approach to the electrode. Finally the diffuse layer is the region beyond the OHP.Schematic representation of a double layer on an electrode (BMD) model. 1. Inner Helmholtz plane, (IHP), 2. Outer Helmholtz plane (OHP), 3. Diffuse layer, 4. Solvated ions (cations) 5. Specifically adsorbed ions (redox ion, which contributes to the pseudocapacitance), 6. Molecules of the electrolyte solventBockris/Devanthan/Müller [edit]In 1963 J. O'M. Bockris, M. A. V Devanthan, and K. Alex Müller[28]proposed a model (BDM model) of the double-layer that included the action of the solvent in the interface. They suggested that the attached molecules of the solvent, such as water, would have a fixed alignment to the electrode surface. This first layer of solvent molecules display a strong orientation to the electric field depending on the charge. This orientation has great influence on the permittivity of the solvent which varies with the field strength. The inner Helmholtz plane (IHP) passes through the centers of these molecules. Specifically adsorbed, partially solvated ions appear in this layer. The solvated ions of the electrolyte are outside the IHP. Through the centers of theseions pass a second plane, the outer Helmholtz plane (OHP). The region beyond the OHP is called the diffuse layer. The BDM model now is most commonly used. Trasatti/Buzzanca [edit]Further research with double layers on ruthenium dioxide films in 1971 by Sergio Trasatti and Giovanni Buzzanca demonstrated that the electrochemical behavior of these electrodes at low voltages with specific adsorbed ions was like that of capacitors. The specific adsorption of the ions in this region of potential could also involve a partial charge transfer between the ion and the electrode. It was the first step towards pseudo-capacitors.[22]Ph.D., Brian Evans Conway within the John Bockris Group At Imperical College, London 1947Conway [edit]Between 1975 and 1980 Brian Evans Conway conducted extensive fundamental and development work on the ruthenium oxide type of electrochemical capacitor. In 1991 he described the transition from ‗Supercapacitor‘ to ‗Battery‘ behavior in electrochemical energy storage and in 1999 he coined the term supercapacitor as explanation for increased capacitance by surface redox reactions with faradaic charge transfer between electrodes and ions.[1][29][30]His "supercapacitor" stored electrical charge partially in the Helmholtz double-layer and partially was the result of faradaic reactions with ―pseudocapacitance‖ charge transfer of electron and protons between electrode and electrolyte. The working mechanisms of pseudocapacitors are electrosorption, redox reactions and intercalation.Marcus[edit source | edit]The physical and mathematical basics of electron charge transfer without making chemical bonds leading to pseudocapacitance was developed by Rudolph A. Marcus. Marcus Theory is a theory to explain the rates of electron transfer reactions – the rateat which an electron can move or jump from one chemical species to another. It was originally formulated to address outer sphere electron transfer reactions, in which the two chemical species only change in their charge with an electron jumping. For redox reactions without making or breaking bonds Marcus theory takes the place of Henry Eyring's transition state theory which has been derived for reactions with structural changes. R.A. Marcus received the Nobel Prize in Chemistry in 1992 for this theory Storage principlesElectrostatic vs electrochemical energy storageCharge storage principles of different capacitor types and their inherent voltage progressionThe voltage behavior of supercapacitors and batteries during charging/discharging differs clearlyIn conventional capacitors such as ceramic capacitors and film capacitors the electric energy is stored in a static electric field permeates the dielectric between two metallic conducting plates, the electrodes. The electric field originates by the separation ofcharge carriers. This charge separation creates a potential between the two electrodes, which can be tapped via an external circuit. The total energy stored in this arrangement increases with the amount of stored charge and the potential between the plates. The amount of charge stored per unit voltage is essentially a function of the size, the reciprocal value of the distance, and the material properties of the dielectric, while the potential between the plates is limited by the dielectric's breakdown field strength. The dielectric controls the capacitor's voltage.Conventional capacitors are also called electrostatic capacitors. The potential of a charged capacitor decreases linearly between the electrodes. This static storage also applies for electrolytic capacitors in which most of the potential decreases over the thin oxide layer of the anode. The electrolyte as cathode may be a little bit resistive so that for ―wet‖ electrolytic capacitors a small amount of the potential decreases over the electrolyte. For electrolytic capacitors with high conductive solid polymer electrolyte this voltage drop is negligible.Electrochemical capacitors do not have a conventional solid dielectric that separates the charge. The capacitance value of an electrochemical capacitor is determined by electrostatic and electrochemical principles:Electrostatic storage of the electrical energy is achieved by charge separation in a Helmholtz double layer at the interface between the surface of a conductor electrode and an electrolytic solution electrolyte. This capacitance is called double-layer capacitance.Electrochemical storage of the electrical energy is achieved by redox reactions with: specifically adsorbed ions from the electrolyte; intercalation of atoms in the layer lattice（晶格层）; or underpotential deposition of hydrogen or metal adatoms in surface lattice sites that results in a reversible faradaic charge-transfer on the electrode. This capacitance is called pseudocapacitance and is faradaic in origin.[5]Double-layer capacitance and pseudocapacitance combine to provide a supercapacitor's capacitance value.[2][3]Because each supercapacitor has two electrodes, the potential of the capacitor decreases symmetrically over both Helmholtz layers, whereby a little voltage drop across the ESR of the electrolyte achieved.Both the electrostatic and the electrochemical storage are linear with respect to the total charge. This linear behavior implies that the voltage across the capacitor is linear with respect to the amount of stored energy. This linear voltage gradient differs from electrochemical batteries, in which the voltage across the terminals remains independent of the charged energy, providing a constant voltage.Electrostatic double-layer capacitanceSimplified view of a double-layer of negative ions in the electrode and solvated positive ions in the liquid electrolyte, detached from each other through a layer of polarized molecules of the solvent.An electrical double layer is generated by applying a voltage to an arrangement of an electrode and an electrolyte. According to the voltage polarity, the dissolved and solvated ions in the electrolyte move to the electrodes. Two layers of ions are generated. One is in the surface of the electrode. The other, with opposite polarity, is the dissolved ions in the adjacent liquid electrolyte. These layers of opposite ions are separated by a monolayer of isolating molecules of the solvent, such as water. The layers of isolating molecule, the inner Helmholtz plane (IHP), adhere by physical adsorption on the surface of the electrode and separate the opposite ions from each other, building a molecular dielectric（电介质）. The amount of charge in the electrode is matched by the same magnitude of counter-charges in the outer Helmholtz plane (OHP). These phenomena can be used to store electrical charges. The stored charge in the IHP forms an electric field that corresponds to the strength of the applied voltage. It is only effective in the molecular layer of the solvent molecules and is static in origin.The "thickness" of a charged layer in the metallic electrode, i.e., the average extension perpendicular to the surface, is about 0.1 nm. It mainly depends on the electron density because the atoms in solid electrodes are stationary. In the electrolyte, the thickness depends on the size of the molecules of the solvent and of the movement and concentration of ions in the solvent. It ranges from 0.1 to 10 nm, and is described by the Debye length. The sum of the thicknesses is the total thickness of a double layer.Field strength [edit]The small thickness of the inner Helmholtz plane creates a strong electric field E. At a potential difference of, for example, U = 2V and a molecular thickness of d = 0.4 nm, the electric field strength will beThe voltage proof of aluminum oxide, the dielectric layer of aluminum electrolytic capacitors is approximately 1.4 nm/V. For a 6.3 V capacitor therefore the layer is 8.8 nm. The electric field is 6.3 V/8.8 nm = 716 kV/mm.The double-layer's field strength of about 5000 kV/mm is unrealizable in conventional capacitors with conventional dielectrics. No dielectric material could prevent charge carrier breakthrough. In a double-layer capacitor the chemical stability of the molecular bonds of the solvent molecules prevents breakthrough.[31]The forces that cause the adhesion are physical, not chemical, forces. Chemical bonds exist within the adsorbed molecules, but they are polarized. The magnitude of the electrical charge that can accumulate in the layers corresponds to the concentration of the adsorbed ions. Up to the electrolyte's decomposition voltage, this arrangement behaves like a capacitor in which the stored electrical charge is linearly dependent on the voltage applied.Structure and function of an ideal double-layer capacitor. Applying a voltage to the capacitor at both electrodes a Helmholtz double-layer will be formed separating the adhered ions in the electrolyte in a mirror charge distribution of opposite polarity. The double-layer is like the dielectric layer in a conventional capacitor, but with the thickness of a single molecule. The early Helmholtz model predicts a constant differential capacitance Cd independent from the charge density, depending on the dielectric constant ε and the charge layer separation δ.If the solvent of the electrolyte is water then with the influence of the high field strength, the permittivity ε is 6 (instead of 80 in normal conditions) and the layerseparation δ ca. 0.3 nm the value of differential capacitance predicted by the Helmholtz model is about 18 F/cm2.[22]This value can be used to calculate capacitance using the standard formula for conventional plate capacitors if only the surface of the electrodes is known. This capacitance can be calculated with:.The capacitance C is therefore greatest in devices made from materials with a high permit tivity ε, large electrode plate surface areas A and a small distance d between plates. The activated carbon electrodes have a surface area in the range of 10 to 40 µF/cm2. The double-layer distance is on the order of a few Angstroms (0.3-0.8 nm). This gives supercapacitors the highest capacitance values among the capacitors.[2][5]Because an electrochemical capacitor is composed of two electrodes the charge distribution in the Helmholtz layer at one electrode can be found in opposite polarity in the Helmholtz layer at the second electrode. The total capacitance value of is that of two capacitors connected in series. Because both capacitances have approximately the same value, the total capacitance is roughly half the capacitance of one electrode.Electrochemical pseudocapacitanceSimplified view of a double-layer with specifically adsorbed ions which have submitted their charge to the electrode to explain the faradaic charge-transfer of the pseudocapacitance.In a Helmholtz double-layer not only a static double-layer capacitance originates. Specifically adsorbed ions with redox reactions, electrosorption and intercalation results in faradaic charge-transfer between electrolyte and surface of an electrodecalled pseudocapacitance. Double-layer capacitance and pseudocapacitance both contribute to the total capacitance value of a electrochemical capacitor.[2][3]The distribution of the amounts of both capacitances depends on the surface area, material and structure the of the electrodes.Redox reactions in batteries with faradaic charge-transfer between an electrolyte and a surface of an electrode are well known since decades. But these chemical processes are associated with chemical reactions of the electrode materials usually with attendant phase changes. Although these chemical processes are relatively reversible, the charge and discharge of batteries often results in irreversibility reaction products of the chemical electrode-reagents. Accordingly, the cycle-life of rechargeable batteries is usually limited, and varies with the battery type. Additional the chemical processes are relatively slow extending the charge and discharge time of the batteries.An essential fundamental difference from redox reactions in batteries arises in supercapacitors, were a fast sequence of reversible redox processes with a linear function of degree of faradaic charge transfers take place. This behavior is the basic function of a new class of capacitance, the pseudocapacitance. Pseudocapacitance comprise fast and reversible faradaic processes with charge transfer between electrolyte and the electrode and is accomplished through reduction-oxidation reactions (redox reactions), electrosorption and intercalation processes in combination with the nonfaradaic formation of an electric double-layer. Capacitors with a high amount of pseudocapacitance are called pseudocapacitors.Applying a voltage at the capacitor terminals the polarized ions or charged atoms in the electrolyte are moving to the opposite polarized electrode forms a double-layer. Depending on the structure or the surface material of the electrode a pseudocapacitance can originate when specifically adsorbed cations pervades(遍及) the double-layer proceeding in several one-electron stages an excess of electrons. The electrons involved in the faradaic processes are transferred to or from valence-electron states (orbitals) of the redox electrode reagent. The electrons enter the negative electrode and flow through the external circuit to the positive electrode were a second double-layer with an equal number of anions has formed. But these anions will not take the electrons back. They are present on the surface of the electrode in the charged state, and the electrons remain in the quite strongly ionized and "electron hungry" transition-metal ions of the electrode. This kind of pseudocapacitance has a linear function within narrow limits and is determined by the potential-dependent degree of coverage of surface with the adsorbed anions from the electrolyte. The storage capacity of the pseudocapacitance with an electrochemical charge transfer takes place to an extent limited by a finite quantity of reagent or of available surface.Discharging the pseudocapacitance the reaction of charge transfer is reversed and the ions or atoms leave the double-layer and move into the electrolyte distributing randomly in the space between both electrodes.Unlike in batteries in pseudocapacitors the redox reactions or intercalation processes with faradaic charge-transfer do not result in slow chemical processes with chemical reactions or phase changes of the electrode materials between charge and discharge. The atoms or ions contribute to the pseudocapacitance simply cling[32]to the atomic structure of the electrode and charges are distributed on surfaces by physical adsorption processes that do not involve the making or breaking of chemical bonds. These faradaic charge transfer processes for charge storing or discharging employed in pseudocapacitors are very fast, much faster than the chemical processes in batteries.Confinement of solvated ions in pores, such as those present in carbide-derived carbon (CDC). As the pore size approaches the size of the solvation shell, the solvent molecules are removed, resulting in larger ionic packing density and increased charge storage capability.The ability of electrodes, to accomplish pseudocapacitance effects like redox reactions of electroactive species, electrosorption of H or metal ad-atoms or intercalation, which leads to a pseudocapacitance, strongly depend on the chemical affinity of electrode materials to the ions sorbed on the electrode surface as well as on the structure and dimension of the electrode pores. Materials exhibiting redox behavior for use as electrodes in pseudocapacitors are transition-metal oxides inserted by doping in the conductive electrode material like active carbon as well as conducting polymers such as polyaniline or derivatives of polythiophene covering the surface of conductive electrode material.Pseudocapacitance may also originates by the structure and especially by the pore size of the electrodes. The use of carbide-derived carbons(CDCs) or carbon nanotubes /CNTs for electrodes provides a network of very small pores formed by nanotube entanglement. These carbon nanoporous with diameters in the range of <2 nm can be referred to as intercalated pores. Solvated ions in the electrolyte can‘t enter these small pores but de-solvated ions which have reduced their ion dimensions are able to enter resulting in larger ionic packing density and increase charge storage capability. The tailored sizes of pores in nano-structured carbon electrodes can maximize ion confinement, increasing specific capacitance by faradaic H2adsorption treatment(?). Occupation of these pores by de-solvated ions from the electrolyte。

新型锂盐LiBC_2O_4F_2在EC_DMC溶剂中的电化学行为_英文_

新型锂盐LiBC 2O 4F 2在EC+DMC 溶剂中的电化学行为高宏权赖延清张治安*刘业翔(中南大学冶金科学与工程学院,长沙410083)摘要：采用差热-热重(TG -DTA)、恒电流充放电和交流阻抗(EIS)分析了二氟草酸硼酸锂(LiODFB)的热稳定性,研究了LiODFB/碳酸乙烯酯(EC)+碳酸二甲酯(DMC)电解液的电化学性能及界面特征.实验结果表明,LiODFB 不仅具有更高的热稳定性,而且在EC+DMC 溶剂中具有较好的电化学性能.与使用LiPF 6/EC+DMC 的电解液相比,锂离子电池应用LiODFB 基电解液在55℃的高温具有更好的容量保持能力;以0.5C 、1C (1C =250mA ·g -1)倍率循环放电,两种电池间的倍率性能差别较小;LiODFB 能够在1.5V(vs Li/Li +)左右在石墨电极表面还原形成一个优异稳定的保护性固体电解质相界面膜(SEI 膜);交流阻抗表明,使用LiODFB 基电解液的锂离子电池仅具有稍微增加的界面阻抗.因此LiODFB 是一种非常有希望替代LiPF 6用作锂离子电池的新盐.关键词：锂离子电池;电解液;二氟草酸硼酸锂;电化学性能;界面特性中图分类号：O646Electrochemical Behaviors of New Lithium Salt LiBC 2O 4F 2inEC+DMC SolventsGAO Hong -QuanLAI Yan -QingZHANG Zhi -An *LIU Ye -Xiang(School of Metallurgical Science and Engineering,Central South University,Changsha410083,P.R.China )Abstract ：The thermal stability of lithium difluoro(axalato)borate (LiODFB)was analyzed by thermal gravimetric -differential thermal analysis (TG -DTA).The electrochemical performance and interfacial characteristics of the LiODFB/ethylene carbonate (EC)+dimethyl carbonate (DMC)electrolyte were studied by constant current charge -discharge and electrochemical impedance spectroscopy (EIS).Results show that LiODFB has higher thermal stability and that the lithium -ion cells using LiODFB salt in EC+DMC solvents exhibit excellent electrochemical pared with the LiPF 6/EC+DMC electrolyte,the lithium -ion cells using LiODFB -based electrolyte have very good capacity retention at 55℃.At 0.5C and 1C (1C =250mA ·g -1)discharge rates,the difference between the rate capability of the two cells is tiny.LiODFB is reduced at about 1.5V (vs Li/Li +)and forms a robust protective solid electrolyte interphase (SEI)film on the graphite surface.EIS tests show that these lithium -ion batteries which use the LiODFB -based electrolyte have a slightly higher interfacial impedance.Therefore,as a new salt,LiODFB is a promising alternative lithium salt for the replacement of LiPF 6in lithium ion battery electrolytes.Key Words ：Lithium -ion battery;Electrolyte;Lithium difluoro(axalato)borate;Electrochemicalperformance;Interfacial property[Article]物理化学学报(Wuli Huaxue Xuebao )Acta Phys.-Chim.Sin .,2009,25(5)：905-910Received:November 20,2008;Revised:January 19,2009;Published on Web:March 3,2009.*Corresponding author.Email:zhianzhang@;Tel:+86731-8876454.国家科技支撑计划(2007BAE12B01)及国家自然科学基金项目(20803095)资助鬁Editorial office of Acta Physico -Chimica SinicaRecent advances in cathode and anode materials have refo -cused attention on electrolytes as the technological bottleneck limiting the operation and performance of lithium -ion battery systems.Whereas,attributes such as cell potential and energy density are related to the intrinsic property of the positive and negative electrode materials,cell power density,calendar -lifeMay 905Acta Phys.-Chim.Sin.,2009Vol.25and safety are dictated by the nature and stability of the elec-trolyte and the electrode-electrolyte interface[1,2].Lithium-ion bat-tery electrolytes of commercialization typically consist of lithium hexafluorophosphate(LiPF6)dissolving in mixture solvents of ethylene carbonate(EC)+dimethyl carbonate(DMC).The high dielectric constant cyclic EC enables the dissolution of lithium salts to sufficient concentrations,and possesses good compati-bility with graphite electrode,but is rather viscous.The linear DMC,on the other hand,is low dielectric constant but its low viscosity and broader temperature window promote rapid ion transport.So they are chosen as components of most lithium-ion battery electrolytes of commercialization.The commonly used LiPF6is the salt of the main choice for lithium-ion batteries of commercialization because of its high solubility and excellent conductivity in alkyl carbonate solvents.Whereas,LiPF6is sen-sitive to trace amounts of moisture,resulting in by-products such as PF5,POF3,HF and LiF and LiPF6is of poor thermal stability. It starts to decompose at40℃,and decomposes totally at80℃[3,4]. Thus the side reactions of LiPF6make it difficult to meet the requirements of high energy density and long cycle life for hybrid electrical vehicle(HEV)application,especially in summer when the ambient temperature around lithium ion batteries for electri-cal vehicles will rise upto70℃.Therefore,studies on new salts to replace LiPF6are attracting more and more attention now[5,6]. In2006,Zhang[7]reported the chemical structure of LiODFB (molecular formula:LiBC2O4F2as shown in Fig.1)that possesses the combined advantages of LiBOB(LiB(C2O4)2)and LiBF4,and shows good electrochemical performances.He found that Li-ODFB could provide a high cycling efficiency for metallic lithi-um plating and stripping on the surface of Cu,and showed good passivation towards Al at high current rate.Recently,in high propylene carbonate(PC)-containing solutions,it is found that LiODFB used as electrolyte salt can provide stable SEI film and low cell impedance,which results in a dramatic improve-ment on both capacity retention and rate performance.Lithium ion batteries with LiODFB have excellent cycling performance even at60℃[8,9].Furthermore,it is found that the addition of small amount of LiODFB to the LiPF6-based electrolyte can sig-nificantly improve both the capacity retention and the power retention of lithium ion batteries.But at the same time it will slightly increase the interfacial impedance of the cells[10].So,thor-ough research on this salt needs to be done in order to get its widely commercial application.LiODFB is attracted attention as soon as it was found because of its excellent electrochemical performances[11,12].But at present research on it was just started,the electrochemical performances of LiODFB in traditional solvents have not been reported.There-fore,LiODFB was dissolved in EC+DMC mixed solvents and was used as electrolyte.The performance behaviors of the Li/ graphite(G)half cells and G/LiCo1/3Ni1/3Mn1/3O2full cells using different two lithium salts were studied,and their interfacial characteristics were analyzed.1Experimental1.1Preparation of electrolyteLiPF6,LiODFB salts and EC,DMC solvents for application in batteries were purchased from Ferro Performance Materials Company,USA.The solvents were purified further through RE-3000rotary evaporator(made in Shanghai Yarong Company,China)and dried over4A molecular sieves until the water content was lower than 2.0×10-5(mass fraction),as determined by METTLER-TOLEDO DL32Karl-Kisher titration(Mettler-Toledo Instruments Co.Ltd., Switz).The base electrolytes used in this work,1.0mol·L-1LiPF6in mass ratio of EC∶DMC being1∶1and1.0mol·L-1LiODFB in mass ratio of EC∶DMC being1∶1,were prepared in an Ar-filled glove box.1.2TG-DTA of the electrolyte saltsA SDTQ-600simultaneous thermogravimetric analyzer(TA Instruments,USA)was used to analyze thermal stability and thermal behavior of LiODFB and LiPF6powders during heating. The samples LiODFB about18.9960mg and LiPF6about 24.1340mg were heated from room temperature to400℃at a heating rate of10℃·min-1in nitrogen and argon mixture flow.1.3Constant current charge-discharge testsThe working electrode of half cells was composed of94% (mass fraction)graphite and6%poly(vinylidene difluoride) (PVDF)binder.The counter and reference electrodes of half cells were lithium foils.The separator was a Celgard2400mi-croporous polylene membrane.The half cells were assembled using2025type coin cells and an appropriate amount of elec-trolyte in an Ar-filled glove box.The charge-discharge perfor-mances of Li/G half cells were evaluated at a constant current of 25mA·g-1(0.1C)with a voltage window0-2.0V(vs Li/Li+) using a LAND CT2001A charge/discharge instrument(Wuhan Jinnuo Electronics Co.Ltd.,China).The positive electrode of full cells was composed of84% (mass fraction)LiCo1/3Ni1/3Mn1/3O2,8%carbon black and8% PVDF binder.The negative electrode of full cells was composed of94%(mass fraction)graphite(G)and6%PVDF binder.The separator was a Celgard2400microporous polylene membrane. The full cells were assembled using2025type coin cells and an appropriate amount of electrolyte in an Ar-filled glove box.The initial charge-discharge capacity and cycling performance of G/ LiCo1/3Ni1/3Mn1/3O2cells were evaluated using a LAND CT2001A charge/discharge instrument.The charge cut-off and the dis-charge cut-off voltages were4.2and2.5V at a constant current of0.1C,respectively.At the same case,the cells were cycled100Fig.1Molecular structure of LiODFB 906No.5GAO Hong -Quan et al .：Electrochemical Behaviors of New Lithium Salt LiBC 2O 4F 2in EC+DMC Solventstimes at high temperature (55℃)and were cycled 20times at0.5C and 1C rates at 25℃.1.4Electrochemical impedance testsEIS was measured with 2025type coin cells which were as -sembled according to the method in Section 2.3in the PAR -STAT 2273electrochemical measurement system (Perkin Elmer Instrument,USA).The Li/G half cells using two kinds of differ -ent electrolytes were first discharged to 0.2V with a consta ntcurrent of 25mA·g -1(0.1C )before the electrochemical impedance of the cells was measured in the frequency range from 10mHz to 100kHz.The G/LiCo 1/3Ni 1/3Mn 1/3O 2full cells using two kinds of different electrolytes were first cycled between 3.0and 4.0V for two cycles with a constant current of 0.1C .Then the cells were constant -voltage -charged to 3.8V before the electrochemical impedances were measured in the frequency range from 10mHz to 100kHz.2Results and discussion2.1Thermal stability analyses of LiPF 6and LiODFB The DTA -TG -DTG curves of LiPF 6and LiODFB are given in Fig.2.In order to more directly analyze the thermogravimetry changes,the derivative thermogravimetry (DTG)curves of LiPF 6and LiODFB are showed.The general information about their thermal behaviors,in terms of stability range,peak temperature and percentage mass loss,are presented in Table 1.As seen from Table 1,LiPF 6show a two -step decomposition mode and LiODFB is three -step.The first mass loss,which generally completes before 100℃is related to the free acid removal.As seen in DTA -TG -DTG curves of Fig.2(A),the DTA profile of LiPF 6salt shows that there is endothermic peak at about 76.85℃between 43.19and 82.75℃.Mass loss is about 4.25%at the stage which is the hydrogenfluoride removal.The thermal decomposition reaction is LiPF 6·HF →LiPF 6+HF ↑[13].Similarly,in DTA -TG -DTG curves of LiOD FB,there is less endothermic peak at about 68.54℃in DTA curve of Fig.2(B)between 56.20and 71.46℃.Mass loss is about 1.28%at the stage.Because the preparation techniques of LiODFB are not clear now,mass loss could be relate to the free acid in products.A low content of this acid in lithium salts is demanded for high -quality lithium -ion battery becausethe existence of free acid promotes severe corrosions of the cur -rent collectors,and leads to further deterioration of the battery perforrmance.The present work shows that the amount of the free acid in LiODFB salt is lower than that in LiPF 6.The main mass loss stage for the salt compounds is the de -composition of their base materials.From DTA curve of LiPF 6,it can be seen that there is obvious strong endothermic peak at about 228.63℃in the temperature range of 143.75-252.28℃and over.Mass loss is about 78.42%at the stage which is due to the completely decomposition reaction of LiPF 6:LiPF 6→LiF +PF 5↑[13].Similarly,there is a big and acuate endothermic peak about 276.29℃in DTA curve of LiODFB between 219.33and 295.47℃.Mass loss is about 41.93%at the temperature range.Subsequently,there is less endothermic peak at about 322.37℃in DTA curve of LiODFB between 295.47and 337.22℃.Mass loss is about 16.12%in TG curve of LiODFB.These mass losses and endothermic peaks may be attribution to unique structure of LiODFB as shown in Fig.1.As indicated by its structure,LiODFB contains the same moieties as LiBOB and LiBF 4.The decompo -sition reaction of LiBOB at 302℃is 2LiB(C 2O 4)2→Li 2C 2O 4+B 2O 3↑+3CO 2↑+3CO [14].The decomposition reaction of LiBF 4at 162℃is LiBF 4→LiF+BF 3[15].Therefore the decomposition pro -cess of LiODFB may contain two decomposition reactions above.From the above analysis,it can be seen that LiODFB has higher thermal stability and much less free acids and can not produce the poisonous PF 5which high reacts with organic sol -vents in electrolyte.The released CO 2may avoid thermal run -way and possibly provides safety protection against abuse oper -ations [7].2.2Elevated temperature cycling performances of G/LiCo 1/3Ni 1/3Mn 1/3O 2cellsT i ,T p ,and T f represent the initial decomposition temperature,the peak temperature of DTA,and the final decomposition temperature,respectively.Table 1Decomposition temperature of TG -DTAFig.2TG -DTA -DTG curves of LiPF 6(A)and LiODFB (B)Salt Stage TG curve Mass loss(%)DTA curve T i /℃T f /℃T p /℃LiPF 6I 43.1982.75 4.2576.85II 143.75252.2878.42228.63LiODFBI 56.2071.46 1.2868.54II219.33295.4741.93276.29III 295.47337.2216.12322.37907Acta Phys.-Chim.Sin.,2009Vol.25Fig.3shows the capacity retention of G/LiCo1/3Ni1/3Mn1/3O2 full cell at55℃with a constant current of0.1C.It shows that LiODFB-based electrolyte has improved cycling performance. When the LiPF6-based electrolyte is used,the cell′s capacity fades very fast.After100cycles,the loss of capacity is close to31%at55℃.When the LiODFB-based electrolyte is used, the cell′s capacity fades with only8%after100cycles.The ini-tial coulombic efficiency of the cell using the LiODFB-based electrolyte is higher than that of the cell using the LiPF6-based electrolyte.It can be showed that the cells using the LiODFB-based electrolyte have not only excellent cycling performance but also higher initial coulombic efficiency.These are related to higher thermal stability of LiODFB salt.Then these advantages of LiODFB are analyzed from interfacial phenomenon with LiPF6counterpart.2.3Interface property of Li/G half cellsThe SEI film layer plays the important role in protecting the graphite surfaces during subsequent cycling;the composition, morphology,and stability of the SEI film are known to critically affect the cycle-and storage-life of a lithium-ion cell[16,17].Fig.4 shows the differential capacity profiles of Li/G half cells using different electrolytes.The cells were cycled at25℃with a con-stant current of0.1C.Only the initial data showing the formation of SEI film are shown in Fig.4.Only one small peak about0.65V(vs Li/Li+)is observed for the cell using LiPF6-based elec-trolyte.This peak can also be observed for cells using LiODFB at a slightly higher potential.This peak is believed to be the result of the reduction of the alkyl carbonate solvents during passiva-tion reaction on the graphite surfaces[18].However,an extra strong peak is observed at about1.5V(vs Li/Li+)for the cell using LiODFB.The peak is believed to be caused by the reduction and polymerization of ODFB-.Liu et al.[10]thinks that the SEI film formed in the electrolyte without LiODFB has more inor-ganic components(such as Li2CO3and LiF)that are less sensitive to the temperature,while the SEI film formed with the elec-trolyte with LiODFB has more organic components that are more sensitive to temperature and has lower impedance at ele-vated temperature.This is beneficial to both remaining higher cycling capacity retention and less initial capacity loss of the cells at high temperature(Fig.3).Graphite negative interfacial impedance is the main contributor to full cell impedance[1].In order to further confirm electrolyte salt effect on interface impedance of surface graphic negative, AC impedances of Li/G half cells using different electrolytes are studied and shown in Fig.5.In all case,the EIS shows either one semicircle or two partially overlapped semicircles,followed by a straight sloping line at the low frequency end.The high frequency semicircle of EIS is resistance of the SEI film on the surface of graphite.The medium frequency semicircle is the charge-transfer resistance.The following straight sloping line at low frequency end is mainly related to diffusion process of lithium ions on the electrode-electrolyte interface.In the potential regions where no electrode reactions take place,the resistance which corresponds to the medium frequency semicircle is so high that its related semicircle disappears,and in this case,the EIS shows only one semicircle followed by a straight sloping line.SEI film can be studied by different semicircles,as shown by Nyquist profiles of EIS in Fig.5.The data show that the cells using LiPF6have a lower interfacial impedance,about12Ωat0.2V.The cells using LiODFB-based electrolyte have a slightly higher impedance, about17Ωat0.2V,because alkyl carbonate electrolytes form a preliminary SEI film on the graphic surface in the0.6-0.7V range before graphic lithiation at0.2V[19].But LiODFB at1.5VFig.3Capacity retention of G/LiCo1/3Ni1/3Mn1/3O2full cells using different electrolytes at0.1C rate and55℃Fig.4First charge differential capacity profiles of Li/G half cells with different electrolytes Fig.5Nyquist profiles of AC impedance of Li/G half cellswith different electrolytes908No.5GAO Hong-Quan et al.：Electrochemical Behaviors of New Lithium Salt LiBC2O4F2in EC+DMC Solventscauses the reduction and polymerization and participates in the SEI film formation that lead to improve thickening of film and increase impedance of film[20],which is disadvantageous to im-prove power capability of the cells.2.4Interface property of G/LiCo1/3Ni1/3Mn1/3O2full cells The differential capacity profiles of G/LiCo1/3Ni1/3Mn1/3O2full cells using different electrolytes are shown in Fig.6.The cells were charged at25℃with a constant current of0.1C,and only the initial data below3V during the first charge are shown in Fig.6to demonstrate the impact of LiODFB on the SEI film formaton.A small peak is observed at about3.0V for each elec-trolyte profile and the peak position is almost the same.This peak can be further related to the peak at0.65V in half cells (Fig.4).The peak with large intensity is observed at about2.2V for the cell containing LiODFB,but not for the cell containing LiPF6.LiODFB dose not participate in the electrochemical re-action on the positive electode through the electrochemical reac-tion[10].Hence,it can be concluded that the peak at2.2V is be-lieved to result from the SEI film layer formed by the LiODFB, and the peak is also related to the extra peak at1.5V in half cell containing LiODFB.This shows that LiODFB forms a protective film on the negative electrode during the initial charge-discharge process from being attacked by other cell components.Nyquist profiles of AC impedance of G/LiCo1/3Ni1/3Mn1/3O2f ull cells with different electrolytes are shown in Fig.7.The full cell using LiODFB-based electrolyte has an impedance of about27Ω,which is17%slightly higher than that of the full cell using LiPF6-based electrolyte(about23Ω),as shown in Fig.7.Therefore,this suggests that the power capability of the G/ LiCo1/3Ni1/3Mn1/3O2full cells could be slightly reduced by com-pletely replacing LiPF6with LiODFB.2.5Rate performances of G/LiCo1/3Ni1/3Mn1/3O2full cells In order to further confirm rate performance,Fig.8shows the electrochemical performances of the G/LiCo1/3Ni1/3Mn1/3O2full cells using the two different electrolytes at0.5C and1C dis-charge rates.At0.5C and1C discharge rates,the rate capability of the cell with the LiODFB-based electrolyte is almost the same as that of the cell with the LiPF6-based electrolyte,and the gap between the two cells was tiny.The initial discharge capacity of the cell using the LiPF6-based electrolyte is higher,about128.6 mAh·g-1.After20cycles,the discharge capacity is still100.7 mAh·g-1,the capacity retention is78.3%.While about117.6 mAh·g-1of the initial discharge capacity of the cell using the LiODFB-based electrolyte decreases to94.1mAh·g-1after20 cycles,the capacity retention is80.0%.The capability fade of the latter is even slower than that of the former.It is very clear that the cells using LiODFB provides a slightly higher impedance of SEI film that leads to a slightly lower rate capacity, and a protective film on surface of anode that leads to better coulombic efficiency and cycling capacity retention.In summary, the cells using the LiODFB-based electrolyte can provide better comprehensive performances.3Conclusions(1)LiODFB has higher thermal stability and much less free acid content,and released CO2possibly provides good safety of cells.(2)The cells using LiODFB-based electrolyte have lower capacity fade than the cells using LiPF6-based electrolyte after 100cycles at55℃,and higher initial capacity retention at the elevated temperature.Fig.6First charge differential capacity profiles of G/ LiCo1/3Ni1/3Mn1/3O2full cells with different electrolytesFig.7Nyquist profiles of AC impedance of G/ LiCo1/3Ni1/3Mn1/3O2full cells with different electrolytes Fig.8Cycling performances of G/LiCo1/3Ni1/3Mn1/3O2full cells using different electrolytes at different dischargerates and25℃909Acta Phys.-Chim.Sin.,2009Vol.25(3)At0.5C and1C discharge rates,the rate capability of the cells with the LiODFB-based electrolyte is almost the same as that of the cells with the LiPF6-based electrolyte after20cycles, and the gap between the two cells is tiny.(4)Interface properties of the cells show that LiODFB is reduced and forms a thickening and protective SEI film on the negative electrode.Although this can increase the impedance of SEI film,the cells still can provide a preferable rate perfor-mance.More work is needed to carry out in the lithium battery of commercialization in the future.References1Abraham,D.P.;Furczon,M.M.;Kang,S.H.;Dees,D.W.;Jansen,A.N.J.Power Sources,2008,180(1):6122Li,F.Q.;Lai,Y.Q.;Zhang,Z.A.;Gao,H.Q.;Yang,J.Acta Phys.-Chim.Sin.,2008,24(7):1302[李凡群,赖延清,张治安,高宏权,杨娟．物理化学学报,2008,24(7):1302]3Amine,K.;Liu,J.;Kang,S.;Belharouak,I.;Hyung,Y.;Vissers,D.;Henriksen,G.J.Power Sources,2004,129(1):144Andersson,A.M.;Edstr觟m,K.J.Electrochem.Soc.,2001,148(10):A11005Sasaki,Y.;Handa,M.;Sekiya,S.;Kurashima,K.;Usami,K.J.Power Sources,2001,97/98:5616Yu,B.T.;Qiu,W.H.;Li,F.S.;Xu,G.X.Electrochemical and Solid-State Letters,2006,9(1):A17Zhang,mun.,2006,8(9):14238Aravindan,V.;Vickraman,P.;Krishnaraj,K.PolymerInternational,2008,57(7):9329Aravindan,V.;Vickraman,P.Solid State Sciences,2007,9(11): 106910Liu,J.;Chen,Z.H.;Busking,S.;Amine,K.Electrochem.Commun.,2007,9(3):47511Kang,S.H.;Abraham,D.P.;Xiao,A.;Lucht,B.L.J.Power Sources,2008,175(1):52612Zhang,S.S.J.Power Sources,2007,163(2):71313Smagin,A.A.;Matyukha,V.A.;Korobtsev,V.P.J.Power Sources,1997,68(2):32614Xu,K.;Zhang,S.S.;Jow,T.R.;Xu,W.;Angell,C.A.Electrochemical and Solid-State Letters,2002,5(1):A2615Lu,Z.R.;Yang,L.;Guo,Y.J.J.Power Sources,2006,156(2): 55516Zheng,T.;Gozdz,A.S.;Amatucci,G.G.J.Electrochem.Soc., 1999,146(11):401417Herstedt,M.;Abraham,D.P.;Kerr,J.B.;Edstr觟m,K.Electrochim.Acta,2004,49(28):509718Chen,Z.H.;Lu,W.Q.;Liu,J.;Amine,K.Electrochim.Acta, 2006,51(16):332219Zheng,H.H.Electrolyte of lithium ion battery.Beijing:Chemical Industry Press,2007:80[郑洪河.锂离子电池电解质.北京:化学工业出版社,2007:80]20Zhang,S.S.;Xu,K.;Jow,T.R.Electrochim.Acta,2006,51(8/9): 1636910。

碳球氧化镍复合材料的制备及其超级电容器性能研究

山东化工SHANDONG CHEMICAL INDUSTRY•6•2020年第49卷碳球/氧化镰复合材料的制备及其超级电容器性能研究刘程成】，王玉锋2$，郭攀1，卞振涛1，王聪1，王红艳1(1•宿州学院，安徽宿州234000；2.安徽创佳安全环境科技有限公司，安徽宿州234000)摘要:采用三步法制备碳球/氧化］复合材料’首先，采用葡萄糖和甘氨酸以水热法制备碳球’其次，以碳球、六水合硝酸］和尿素为原料，在水热条件下合成前驱物’最后，在350七下将前驱物d烧得到碳球/氧化］复合材料’利用XRD和SEM等方法对材料的结构形貌进行表征’利用循环伏安法(CV)和恒流充放电法(GCD)探究材料的电化学性能’实验结果表明，通过空气d烧的样品中氧化］颗粒较小且分布比较均匀，导电性良好，相同电流下比电容最大，电化学性能优良’关键词:水热法;碳球/氧化］复合材料;超级电容器中图分类号:TM53文献标识码：A文章编号：1008-021X(2020)23-0006-03Preearation of Carbon Sphere/nicCel OxiCe Composite and Its Supercapacitor Performance Liu Chegcheng',Wang Yufeng2,Guo Pan1，—ian.Zhentao1,Wang Cong',Wang Hongyan1(1.Suzhou University,Suzhou234000,China；2.Anhui Chuangjib Safety and Environment Technology Co.,Ltd., Suzhou234000,China)Abstract:Carbon spheres/nickei oxide composites were prepared by a three-step method.Firstly,carbon spheres were prepared by hydrothermal method using glucose and glycine.Second-,the precursoe was synthesized from carbon spheres,nickei nitrate hexahydrate and urea under hydro thermai conditions.Finaty,the precursor as calcined at350壬th obtain carbon spheres/nickei oxide composites.The structure and morphology of the materials were characterized by XRD and SEM.The electrochemicai properties of the materials were investigated by cyclio voltammetry(CV)and galvanostatic charye discharye(GCD)-The results show that the nickei oxide particles in the samples calcined by aio were small and even-distriauted,and the conductivith was good.The specific capacitancc was the laryest under the same current,and the electrochemical performance was excellent.Key words:hydrothermal method；carbon sphere/nickel oxide composite；supercapacitor与普通电池相比，超级电容器因其电阻低、循环性好、功率密度高等优点而成为研究的热点［1］。

以乙酰丙酮金属盐为前驱体可控合成无机磁性、金属以及半导体纳米晶

本论文主要工作包括以下几个部分： 1、在第二章中，本章介绍了一种尺寸可控合成高质量单分散 Fe3O4、Ag、以及 Fe3O4-Ag 双功能异质结纳米晶的方法。在合成 Fe3O4 中，采用廉价的十二醇作为还原剂，简单的通过控制各种反应物之间的比例达到对尺寸控制的目的。该方法操作简单，避免了以前 “种子二次生长法”的麻烦。在合成 Ag 纳米晶中，我们采用 Agacac 为 Ag 的前驱体，通过控制反应温度达到对 Ag 纳米晶尺寸的控制。用不同尺寸的 Fe3O4 纳米晶作为种子，还成功的合成出各种尺寸的 Fe3O4-Ag 双功能异质结纳米晶。 2、在第三章中，本章主要工作是将乙酰丙酮金属盐作为一种普适的前驱体推广到了各种半导体纳米材料的合成当中。初步的验证了乙酰丙酮金属盐在各种纳米材料合成中的普适性。利用这种方法可以在尺寸可控的基础上，合成出各种高质量三元、二元的半导体纳米晶。另外，通过对表面活性剂种类的选择，可以实现对合成纳米晶形貌的控制。 3、在第四章中，以乙酰丙酮金属盐为原料合成 Sn-DDT 配合物，该配合物可以诱导合成具有良好筒状自组装行为的片状六边形 Cu2S 纳米晶。通过实验条件的调节可以得到一维的筒状、二维竹筏状和三维的层状自组装。另外由于 Sn-DDT 配合物的引入使得各个 Cu2S 颗粒之间的距离减小，导电性增强。这种全新的构筑形貌可控的具有良好组装的纳米晶的方法可能会为合成领域以及器件的组装领域提供新的途径。
This thesis includes the following main aspects: In chapter 2, high-quality, monodisperse, and size-controlled Fe3O4, Ag, and bifunctional Fe3O4/Ag heterodimer nanocrystals (NCs) have been synthesized successfully. In the synthesis of Fe3O4 NCs, dodecanol was chosen as the substitute of 1, 2-hexadecanediol and “size control” was achieved by simply adjusting the proportion among the ligands instead of utilizing seed-mediated growth. In the synthesis of Ag NCs, organometallic silver acetylacetonate (Agacac) was used as precursors and tunable particle size

超级电容器复合电极材料应用研究进展

第23卷第3期2009年9月上　海　工　程　技　术　大　学　学　报J OURNAL OF SHAN GHAI UNIV ERSIT Y OF EN GIN EERIN G SCIENCEVol.23No.3Sep.2009 文章编号:1009-444X (2009)03-0270-07收稿日期:2009-05-05基金项目:上海市科委纳米专项项目(095nm052500);上海工程技术大学优秀学位论文培育专项资助项目(B8909080116)作者简介:冯继成(1986-),山东潍坊人,在读硕士,研究方向为功能材料与催化技术.超级电容器复合电极材料应用研究进展冯继成,刘　萍,赵家昌,唐博合金,徐菁利(上海工程技术大学化学化工学院,上海201620)摘要:对超级电容器复合电极材料的研究进展进行了综述.超级电容器是一种新型能源器件,性能介于传统电容器和电池之间,具有高能量密度、高功率密度、循环寿命长和污染小等特点.超级电容器的电极材料包括炭材料、金属氧化物和导电聚合物,由于复合电极材料能利用各组分间的协同效应提高整体性能,所以比单纯的炭材料、氧化物以及导电聚合物具有更好的应用前景.关键词:超级电容器;复合电极材料;电化学性能中图分类号:TM 53 文献标志码:AApplication R esearch on Composite Materials forE lectrochemical C apacitorsFEN G Ji 2cheng ,L IU Ping ,ZHAO Jia 2chang ,TAN G Bo 2he 2jin ,XU Jing 2li(College of Chemistry and Chemical Engineering ,Shanghai University of Engineering Science ,Shanghai 201620,China )Abstract :The supercapacitor is a new type elect rochemical energy storage device between t he traditional dielect ric capacitor and t he battery.The supercapacitor can p rovide high energy density ,high power den 2sity and has long cycle life and less pollution.Elect rode materials mainly include carbon materials ,metal oxides ,and conducting polymers.The recent progress of t he compo site electrode materials for supercapa 2itors has been reviewed and int roduced in detail due to t heir better application perspective.K ey w ords :supercapacitor ;composite elect rode materials ;elect rochemical performance 超级电容器(Supercapacitor )具有高能量密度、高功率密度、长循环寿命和宽使用温度范围等特点.超级电容器在电力、铁路、绿色能源、军品、航空航天领域的各种快速大功率启动系统、无人值守与移动能源系统和后备电源系统等方面都有极其重要的应用价值.从结构上看,超级电容器主要由极化电极、电解液、集流体、隔膜以及相应的辅助部件组成.超级电容器广泛的应用前景和潜在的巨大商业价值引起了众多研究者的关注.超级电容器的研究主要集中于高性能电极材料的制备.目前,常用的电极材料主要有炭材料、金属氧化物和导电聚合物(Electrically Conducing Polymer ,ECP ).复合材料,例如炭/氧化物、炭/ECP 、氧化物/ECP 和其他复合物等.由于能利用各组分间的协同效应提高　第3期冯继成,等:超级电容器复合电极材料应用研究进展整体性能,所以,复合电极材料已成为目前人们研究的热点.1　炭/金属氧化物超级电容器炭/氧化物复合材料涉及到的氧化物有钌氧化物(RuO2)[1-9]、锰氧化物(MnO2)[10-14]以及其他氧化物.1.1　钌氧化物/炭钌氧化物/炭复合材料的制备方法较多,方法之一是先通过在炭材料上引入钌,再通过别的方法使钌转化为钌氧化物.Yan等[1]开发了一种高效的方法,用Ru来修饰多壁碳纳米管(MWCN T).通过油包水反相微乳液法制得Ru固定于MWCN T 上.循环伏安测试表明,在同一电解质溶液中处理过的钌氧化物电极明显高于原始的MWCN T. Fang等[2]通过新型RuO2纳米复合物来提高超级电容器的性能.RuO2纳米复合物是通过在MWC2 N T阵列上直接溅射Ru.X射线光电子能谱(XPS)、高分辩透射电镜(HR TEM)和选区电子衍射(SA ED)测试表明,制得的纳米颗粒是由结晶Ru为核,RuO2为外壳组成.RuO22CN T复合材料比电容达1380F/g,充放电速率高达600mV/s,循环寿命达5000次.浸渍法在超级电容器复合材料制备也有相关报道.He等[3]首次采用化学浸渍法制备了水合钌氧化物/活性炭黑(ACB)复合物.测试表明,随着RuO x的增多,等效串联电阻增大.Li等[4]通过RuCl3・x H2O溶液浸渍有序中孔炭CM K23, NaO H为沉淀剂,后在80～400℃N2气氛下焙烧制得钌氧化物/有序中孔炭复合物.钌氧化物的组成含量(质量分数,下同)为10.0%～30.7%.随RuO2含量的增加,比电容增大,含量最高时比电容达633F/g.复合电极的倍率性能随RuO2的增大而变差,这是由于等效串联电阻(ESR)增大的缘故.Pico等[5]用RuCl3・0.5H2O 溶液浸渍炭纳米管(CN T),过滤后用NaO H处理,再在150℃下热处理2h得复合材料. RuO2・x H2O含量低于11%时,该微粒随RuO2・x H2O量的增加从2nm到4nm.比电容高达840 F/g.Dandekar等[6]先以RuCl3制备钌胶体,通过浸渍不同含量的RuO x(O H)到椰壳活性炭中制备复合材料.复合材料在1M的H2SO4中的比电容为250F/g.其他方法制备复合材料也曾有相继报道.如电沉积法、热分解法等.K im等[7]采用电沉积法获得了炭/钌氧化物复合材料.在CN T薄膜基底上电沉积具有三维多孔结构的纳米尺度钌氧化物.作为比较,在Pt片和炭纸基底上制备了钌氧化物.扫描电镜(SEM)和透射电镜(TEM)的结果表明,在MWCN T上电沉积厚度为3nm钌氧化物层.与Pt 片和炭纸基底上沉积的钌氧化物相比,在CN T薄膜上沉积的钌氧化物不仅有1170F/g的较高比电容,还有更好的倍率性能,这是由于其电极构件中包含一层薄的具有三维纳米孔的CN T基底上的电活性材料.Lee等[8]采用热分解法制备了RuO2・x H2O和V GCF(纳米超长碳纤维)/RuO2・x H2O 纳米复合物.分析测试结果表明:扫描速率为10mV/s, RuO2・x H2O的比电容为410F/g;V GCF/RuO2・x H2O复合材料的比电容为1017F/g,扫描速率为1000mV/s;RuO2・x H2O的比电容为258F/g, V GCF/RuO2・x H2O复合材料的比电容为824 F/g.RuO2・x H2O和V GCF/RuO2・x H2O循环10000次后比电容值分别保留为初始值的90%与97%.Lee等[9]报道了MWCN T和钌氧化物形成的复合薄膜的超电容特性.RuO2涂饰的MWCN T三维纳米孔结构,促进了MWCN T薄膜的电子和离子传递.测试了负载不同RuO2含量的RuO2/ MWCN T复合材料,其比电容最大值为628F/g,比MWCN T的能量密度高出约3倍.1.2　锰氧化物/炭由于贵金属氧化物的价格昂贵,其他氧化物如锰氧化物/炭复合材料的研究也成为热点.锰氧化物/炭复合材料的制备,报道中大多用高锰酸钾(KMnO4)为锰源.Chen等[10]将MWCN T先浸在沸腾的硫酸(H2SO4)中分散、搅拌的同时加入KMnO4粉末后,H2SO4在水溶液中形成沉淀,在MWCN T上生长了单晶α-MnO2纳米棒.其平均粒径为15nm,能够非常密集地附着于MWCN T. MWCN Ts/α-MnO2纳米棒机械混合的超级电容器有更好改性.Subramanian等[11]首次研究了在高充放电电流(2A/g)下仍有长循环性能的无定形MnO2和单壁炭纳米管(SWCN T)组成的复合物.将SWCN T 在磁力搅拌下分散在KMnO4饱和溶液中,混合均匀后逐滴加乙醇,形成沉淀.掺量为20%MnO2的・172・上海工程技术大学学报第23卷　复合物,在循环750次后仍具有良好的库仑效率(75%)和比电容(110F/g).Li等[12]采用化学共沉淀法,将炭气凝胶先加到KMnO4中,之后,再加Mn(C H3COO)2・4H2O 制得MnO2・x H2O/CRF复合物.研究结果表明, MnO2・x H2O/CRF复合材料有良好的电化学性能,高度的可逆性以及良好的充放电性能.MnO2・x H2O负载量为60%时,复合材料的比电容达226.3F/g,而单纯的炭气凝胶的比电容仅为112 F/g.另外,还有其他的制备锰氧化物/炭复合材料的方法.Li等[13]采用电泳沉积法制得MnO2/MWC2 N T复合材料形成的薄膜电极.通过改变沉积时间和电压制得厚度在1～20μm的薄膜.材料孔径为10～100nm.电解液为0.1M的Na2SO4溶液,电压范围为0～1.0V,标准甘汞电极为标准电极时测得的循环伏安曲线较理想,并且有较大的比电容.复合材料的比电容高于无MWCN T,比电容随膜厚度和扫描速率的增加而减小.Raymundo等[14]通过水介质中的化学共沉淀法制得无定形MnO2,其具有相对较高的表面积. CN T被作为炭黑的替代添加剂来提高制造电容器的锰氧化物电极电导率.结果表明,CN T能有效地增加电容并且提高α2MnO2・n H2O电化学性能,α2MnO2・n H2O电极比用炭黑为添加剂有更好的电容性能.该性能的提高得益于CN T的高度缠绕形成了开放中孔网络,使得体相MnO2容易被离子接近.在性能优化方面需要控制电解质p H值,以避免发生不可逆反应,使负极由Mn(Ⅳ)变成Mn(Ⅱ),正极由Mn(Ⅳ)变成Mn(Ⅶ).1.3　其他氧化物/炭其他氧化物如镍氧化物和钒氧化物与炭复合材料也做了研究.Lee等[15]通过简单的化学沉淀法制备了超级电容器氧化镍NiO/CN T纳米复合物.NiO中的CN T网络显著提高:1)通过形成CN T导电网络提高了NiO主体的电导率;2)通过提高比表面积增加了氧化还原反应的活性位.CN T含量达10%可以提高比电容34%.Kud等[16]研究了高倍率五氧化二钒V2O5凝胶/炭复合材料插层电极材料.将钒与双氧水H2O2溶液反应制得V2O5溶胶,将乙炔黑、丙酮一起加到V2O5溶胶中得均相沉淀.将无定形V2O5和炭负载在多孔镍集流体上,在120℃下加热得到电极.在高氯酸锂LiClO4/聚碳酸酯PC或六氧磷酸锂Li PF6/丁内酯(γ-BL)电解液中测试其电性能.复合材料中V2O5和炭的比为0.7时,能出现理想电容的54%,即基于V2O5的360mAh/g (4.2～2.0V),放电速率达到150C或者54A/g V2O5.利用扩散模型,假设D=10-12cm2/s,模拟放电曲线,主客体系统的扩散长度估计为30～50 nm.在20C的倍率下,循环几千次后可逆性仍非常好,无容量损失.由于金属氧化物及其水合物在电极/溶液界面发生可逆法拉第反应,可产生远大于炭材料双电层电容的法拉第准电容,因而引起了研究者的兴趣.目前的工作重点主要围绕以下4个方面:1)用各种方法制备大比表面积的贵金属氧化物及其水合物;2)把贵金属氧化物及其水合物与其他材料复合,以达到既减少用量又提高材料比容量的目的;3)寻找其他的廉价材料代替贵金属氧化物及其水合物以降低材料成本;4)寻找合适的电极材料组装混合超级电容器.其中,最关键的是合成新型的复合材料,以提高超级电容器的能量密度.金属氧化物及其水合物通过在电极/溶液界面发生氧化还原反应产生的法拉第准电容来存储能量的储能机制,虽然使其具有较大的比容量,但由于该类材料的结构(一般情况下是晶体)不利于电解质的渗透,电极材料与电解质溶液接触机会少,因而导电性差,材料的利用率不高,需进一步提高材料的比表面积和孔容量予以改善.而金属氧化物及其水合物复合材料,不仅能弥补单纯金属氧化物及其水合物的不足,而且还能减少金属氧化物及其水合物的用量,降低材料成本,提高材料的比容量.2　炭/导电聚合物炭/导电聚合物(ECP)复合材料结合了ECP 较高的比电容以及炭快速的充放电双电层电容和良好的机械性能.与CN Ts/金属氧化物复合材料相比,CN Ts/ECP复合材料,不仅可提高超级电容器的比电容量,还可降低成本,并且其法拉第准电容效应也较稳定.研究较多的ECP材料主要有聚苯胺(PAn)、聚噻吩(P Th)、聚并苯(PAS)、聚吡咯(PPy)和聚乙烯二茂铁(PV F)等.・272・　第3期冯继成,等:超级电容器复合电极材料应用研究进展 2.1　炭/聚苯胺通过微波聚合、原位化学聚合、界面聚合、电化学聚合、电沉积和原位沉积等方法可以制得炭/ PAn复合材料.MWCN T/PAn的复合较为多见,该复合材料有较好的倍率性能,电容的保持性较好.Mi等[17]通过微波辅助聚合快速制备了MWC2 N T/PAn复合物.TEM显示这种复合材料是一种复合核壳结构的聚苯胺层(50～70nm).能量密度为22W・h/kg时的比电容为322F/g,比单纯的MWCN Ts高出12倍.Dong等[18]通过原位化学氧化聚合法制备了MWCN T/PAn复合物,并作为一种新型的电极材料.复合物的比电容高达328 F/g.Sivakkumar等[19]采用界面聚合法制备了PAn纳米纤维.在1.0A/g的恒电流下其初始比电容达554F/g.通过原位化学聚合制备MWC2 N T/PAn复合物.其比电容达606F/g,循环稳定性好.SWCN T基复合材料也做了相关研究,Gupta 等[20]通过在SWCN T上电化学聚合聚苯胺得到复合物PAn/SWCN T,在1M的H2SO4电解液中测试其电性能.复合物的比电容、比能量和比功率比纯的PAn和SWCN T高.沉积73%PAn在SWC2 N T,其比电容、比能量和比功率分别为485F/g,228W・h/kg 和2250W/kg.Gupta等[21]是通过在电位为0.75 V(参比电极为饱和甘汞电极)下,在SWCN T上原位沉积PAn而得到PAn/SWCN T复合物.研究结果表明,复合物的比电容强烈地受其微结构的影响,而微结构是与PAn沉积在SWCN T上的质量含量相关.最佳条件是:最高比电容为463F/g (10mA/cm-2),PAn的含量为73%.比电容在第一个500次循环后仅降低5%,而再接下来的1000次循环后仅仅降低1%,由此说明该复合材料有较好的稳定性.2.2　炭/聚吡咯Ham等[22]通过吡咯单体的原位聚合在SWC2 N T上包覆 T表面部分被PPy覆盖.聚吡咯包覆的纳米管用LiClO4掺杂并与Kynar FL EX 2801粘接剂相混合来制成超级电容器复合电极.复合电极的比电容高于PPy/粘接剂/炭黑.这是由于其比表面积大,而且SWCN T的光表面具有较高电导率.Oh等[23]通过SWCN T2PPy的甲醇分散液的真空抽滤制得由SWCN T和掺杂PPy组成的具有高度孔隙率的薄片.研究结果显示,当这种复合材料的摩尔比为1∶1时,能达到最高的比电容131 F/g(在1M氧化钠(NaCl)电解液中).Wang等[24]通过吡咯(Py)和SWCN T的均相混合物或吡咯和功能化SWCN T的悬浮液的电聚合制备得到复合薄膜.由于CN T的中孔结构易于达到的电极/电解液界面使得充放电过程非常快.此外,由于CN T的高电导率和中孔结构,复合薄膜的电阻较低,在深放电态时仍然具有理想的电容行为.相反地,纯PPy薄膜由于电导率低、在放电(还原)态体积收缩,而具有较大的电阻和较差的电容特性.另一方面,在PPy/功能化CN T复合膜中,PPy被固定的功能化CN T所掺杂.在还原态, PPy链呈中性,功能化CN T上的负电荷必须被具有较小尺寸的阳离子所平衡.阳离子的平衡行为可以被进一步的离子迁移极化所抵消.因此,PPy/ SWCN T和PPy/功能化SWCN T复合薄膜的比电容在200mV/s的扫描速率下分别达到144F/g 和200F/g.用电化学聚合法将PPy沉积在SWC2 N Ts表面形成复合材料,既发挥了PPy优良的导电性能又利用了SWCN Ts定向特性,在提高SWCN Ts比容量的同时还提高了超级电容器的充放电允许电压,并改善了其循环性能.2.3　炭/其他聚合物Lota等[25]直接在MWCN T上通过PEDO T (聚3,4-乙烯聚氧噻吩))和CN T的均相混合物制得复合物.研究表明,由于纳米管的开口中孔网络结构,易于达到的电极/电解液界面使得复合材料充电速率比较快,在充放电循环中具有高效的可逆能量贮存.复合材料的比电容为60～160F/g,并且有很好的循环性能.由于PEDO T的密度较大,所以复合材料的体积能量密度较大.Gallegos等[26]考察了MWCN T/Cs2PMo12复合物薄膜电极组成的对称超级电容器的电性能,聚乙烯醇PVA为粘结剂.分析测试表明,复合材料在电流为200mA/g下,比电容为285F/g,其能量密度高于纯CN T电极的.另外,由于该复合材料中PEDO T有较高的密度,其最主要的优势在于其体积比能量较高.Frackowiak等[27]研究了与MWSCN T复合的3类导电聚合物,即PAn,PPy和PEDO T作为超级电容器电极材料的性能.研究结果表明,CN T 的作用是作为导电聚合物在复合物中均匀分布的骨架.众所周知,纯的导电聚合物机械性能差,因此・372・上海工程技术大学学报第23卷　炭纳米管在复合物的长循环中起到避免导电聚合物活性材料机械变化(收缩和破碎)的作用.此外,在CN T存在的条件下,改善了电荷转移使得其充放电速率较快.CN T合适的组成含量为20%.不同的非对称超级电容器,工作电压从0.6～1.8V,比电容可达100～330F/g.值得一提的是这种复合材料无需加粘结剂.3　氧化物/导电聚合物鉴于上述炭基材料,超级电容器还有其他基材料合成复合材料,如氧化物导电聚合物.Sharma等[28]在抛光石墨基底上通过电化学方法制备了氧化锰嵌入PPy纳米复合薄膜电极. MnO2和PPy的共沉积使得多孔的PPy母体为MnO2纳米粒子提供了较高的活性表面.另外, MnO2纳米粒子在聚合物链上成核,提高了复合物的电导率和稳定性.复合材料有了巨大的改性,比电容达620F/g,而单纯的MnO2比电容仅为225 F/g,单纯的PPy仅为250F/g.Liu[29]采用界面聚合法将苯胺聚合在3,42乙烯二氧噻吩和苯乙烯磺酸中,得到三维聚3,42乙烯二氧噻吩22聚苯胺母体.由于减短了电子在共轭聚合链上的传递,将PAn引入到PEDO T2PPS中增强了电导率.通过电沉积制得MnO2在PEDO T2PSS2PAn三维母体中的复合电极材料.循环伏安法测试结果表明,只有PEDO T2 PSS时的比电容为0.23F/g,只有PEDO T2PSS2 PAn时的比电容为6.7F/g,而PEDO T2PSS2PAn 2MnO2的比电容为61.5F/g.Sun等[30]在通过动电位沉积制得了聚苯胺和锰氧化物(MnO x)杂化膜.锰氧化物中锰离子主要是+2,+3和+4价,这种复合材料能使比电容提高44%(与PAn相比).测试结果表明,在1000次充放电完毕之后,比电容仍然保持原来的90%,库仑效率为98%.Zhou等[31]通过KMnO4溶液氧化苯胺薄膜在多孔炭电极上化学沉积了锰氧化物和聚苯胺复合薄膜.复合物在0.1M的Na2SO4溶液中具有良好电容行为.复合材料比电容能达到500F/g,循环5000次后能保留初始电容的60%.4　其他复合物复合材料由于能利用各组分间的协同效应提高整体性能,已成为目前人们研究的热点.除上述3种复合材料以外,超级电容器复合材料还有如CN T/PPy/水合MnO2等形式的复合物.Sivakkumar等[32]采用原位化学法制备CN T/ PPy/水合MnO2三元复合物.同时制备CN T/水合MnO2、PPy/水合MnO2等二元复合物进行比较.测试结果显示,扫描速率为20mV/s,CN T/ PPy/水合MnO2复合材料、CN T/水合MnO2、PPy/水合MnO2的比电容分别为281F/g、150 F/g和35F/g;扫描速率变为200mV/s,比电容分别为209F/g、75F/g和7F/ T/PPy/水合MnO2复合材料较高的比电容,以及在高扫描速率下的良好的保持性,仅降低25%.Song等[33]为了提高化学制备的聚苯胺电极的循环稳定性,将其与萘酚复合.与纯聚苯胺电极相比,复合电极的循环性能得到改善,比电容提高.测试结果显示,扫描速率为100mV/s,比电容为475F/g;扫描速率为1000mV/s,比电容为375F/g.5　结　语超级电容器要想满足市场的需求,必须使电极材料具有以下特点:比电容高、比表面积大、电阻率小(小于0.1Ω/cm)、循环寿命长和成本低等.复合材料作为超级电容器电极材料的研究,已引起了越来越多的化学家、物理学家和材料学家的研究兴趣,取得了很大的进展.超级电容器的研究主要集中于高性能电极材料的制备.目前,常用的电极材料主要有炭材料、金属氧化物和ECP.复合材料,例如炭/氧化物、炭/ECP、氧化物/ECP和其他复合物等.由于能利用各组分间的协同效应提高整体性能,比单纯的炭材料、氧化物以及导电聚合物具有更好的应用前景.因此,高能量密度和高功率密度的高性能超级电容器复合电极材料已成为目前人们研究的热点之一.参考文献:[1]　YAN S C,QU P,WAN G H T,et al.Synthesis ofRu/multiwalled carbon nanotubes by microemulsionfor electrochemical supercapacitor[J].Materials R e2search Bulletin,2008,43(10):2818-2824.[2]　FAN G W C,CH YAN O,SUN C L,et al.ArrayedCNx N T2RuO2nanocomposites directly grown on・472・　第3期冯继成,等:超级电容器复合电极材料应用研究进展 Ti2buffered Si substrate for supercapacitor applica2tions[J].E lectrochemistry Communications,2007,9(2):239-244.[3]　H E X J,GEN G Y J,O KE S,et al.Electrochemicalperformance of RuOx/activated carbon black 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Metals,2008,158(15):638-641.[24]　WAN GJ,XU Y L,CH EN X,et al.Preparation andelectrochemical characterization of porous SWN T2PPy nanocomposite sheets for supercapacitor appli2cations[J].Composites Science and T echnology,2007,67(14):2981-2985.[25]　LO TA K,KHOM EN KO V,FRAC KOWIA K E.Capacitance properties of poly(3,42ethylenedioxy2thiophene)/carbon nanotubes composites[J].Journalof Physics and Chemistry of Solids,2004,65(2-3):295-301.[26]　GALL EGOS A K,ROSAL ES R,BARIBARAC M,et al.Electrochemical supercapacitors based on novelhybrid materials made of carbon nanotubes and poly2oxometalates[J].E lectrochemistry Communications,2007,9(8):2088-2092.[27]　FRAC KOWEA K E,KHOM EN KO V,J U REWICZJ,et al.Supercapacitors based on conducting poly2mers/nanotubes composites[J].Journal of Pow erSources,2006,153(2):413-418.[28]　SHARMA R K,RASTO GI A C,DESU S B.Man2ganese oxide embedded polypyrrole nanocompositesfor electrochemical supercapacitor[J].E lectrochimicaActa,2008,53(26):7690-7695.[29]　L IU F J.Electrodeposition of manganese dioxide inthree2dimensional poly(3,42ethylenedioxythio2phene)2poly(styrene sulfonic acid)2polyaniline forsupercapacitor[J].Journal of Pow er Sources,2008,182(1):383-388.[30]　SUN L J,L IU X X,L AU K K,et al.Electrodeposit2ed hybrid films of polyaniline and manganese oxidein nanofibrous structures for electrochemical super2capacitor[J].E lectrochimica Acta,2008,53(7):3036-3042.[31]　ZHOU Z H,CA I N C,ZHOU Y H.Capacitive ofcharacteristics of manganese oxides and polyanilinecomposite thin film deposited on porous carbon[J].Materials Chemistry and Physics,2005,94(2-3):371-375.[32]　SIVA KKUMAR S R,KO J M,KIM D Y,KIM BC,et al.Performance evaluation of CN T/polypyr2role/MnO2composite electrodes for electrochemicalcapacitors[J].E lectrochimica Acta,2007,52(25):7377-7385.[33]　SON G R Y,PAR KJ H,SIVA KKUMAR S R,et al.Supercapacitive properties of polyaniline/Nafion/hy2drous RuO2composite electrodes[J].Journal ofPow er Sources,2007,166(1):297-301.(上接第259页)2　结　语利用不动点求迭代数列的极限是一种常见的方法.通过数列的迭代形式,构造出相应的迭代函数(迭代函数要满足一定的条件),求出函数的不动点,用不动点去构造新的数列(通常是等差数列[4]或者等比数列),从而得出所求迭代数列的通项,并判断极限值是否存在.参考文献:[1]　钱颂迪.运筹学[M].(第2版).北京:清华大学出版社,1990.[2]　綦建刚.极限收敛定理在迭代数列中的应用[J].山东师范大学学报(自然科学版),2004,19(2):96-98. 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电化学谱学表征方法的应用与发展

物理化学学报Acta Phys. -Chim. Sin. 2024, 40 (3), 2304040 (1 of 19)Received: April 24, 2023; Revised: May 19, 2023; Accepted: May 22, 2023; Published online: May 31, 2023. *Correspondingauthors.Emails:**********.cn(F.L.)******************.cn(S.Z.)The project was supported by the National Key Research and Development Program of China (2020YFB1505800) and the National Natural Science Foundation of China (21925404, 22075099, 21991151).国家重点研发计划(2020YFB1505800)和国家自然科学基金(21925404, 22075099, 21991151)资助项目© Editorial office of Acta Physico-Chimica Sinica[Review] doi: 10.3866/PKU.WHXB202304040 Application and Development of Electrochemical Spectroscopy MethodsYue-Zhou Zhu 1, Kun Wang 1, Shi-Sheng Zheng 2,*, Hong-Jia Wang 1, Jin-Chao Dong 1, Jian-Feng Li 1,*1 State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University,Xiamen 361005, Fujian Province, China.2 School of Advanced Materials, Peking University Shenzhen Graduate School, Shenzhen 518000, Guangdong Province, China.Abstract: The theoretical and experimental technologies used for electrochemical characterization methods, which are essential for determining surface structures and elucidating electrochemical reaction mechanisms, have been significantly improved after more than two centuries of development. Traditional chemical methods like cyclic voltammetry (CV) can provide the exact electrochemical reaction rate in different potential ranges, which is beneficial for identifying the electrochemical performance of electrocatalytic materials. However, traditional chemical methods alone are often inadequate when it comes to achieving a deep understanding of reaction mechanisms. In this regard, spectroscopic methods, whichare powerful tools to identify the active sites and intermediate species during electrochemical reactions, are widely applied to elucidate the electrochemical mechanism at a molecular or even atomic level. In this review, three molecular-vibration-spectroscopy-based electrochemical characterization technologies, viz., infrared (IR) spectroscopy, surface-enhanced Raman spectroscopy (SERS), and sum frequency generation (SFG) spectroscopy, are comprehensively reviewed and discussed. IR, SERS, and SFG are all non-destructive spectroscopic techniques with ultra-high surface sensitivity and are indispensable when detecting surface species during electrochemical reactions. Consequently, researchers have strived to combine these spectroscopic techniques with basic electrochemical instruments. In fundamental electrochemical research, detecting electrochemical reactions in model single-crystal systems and determining the structure of interfacial water molecules have been two major research topics in recent years. Single-crystal surfaces are important in fundamental electrochemical research because of their defined atom arrays and energy states, serving as model systems to help bridge experimental results and theoretical calculations. Meanwhile, the structure of interfacial water influences most electrochemical reaction processes, and as such, probing interfacial water structures is a challenging but valuable target in fundamental electrochemical research. Additionally, the application of electrochemical spectroscopic methods to analyze fuel cells has become important, and this review covers recent SERS studies of oxygen reduction reactions (ORR) and hydrogen oxidation reactions (HOR) in hydrogen fuel cells. Concurrently, electrochemical IR and SFG studies on the electrooxidation of small organic molecules are discussed. Finally, owing to the significance of lithium-ion batteries, studies of electrochemical spectroscopic methods on solid electrolyte interphase (SEI) and cathode-electrolyte interface (CEI) are becoming increasingly important and are introduced here. In conclusion, recent advances and the future developments of electrochemical spectroscopy methods are summarized in this review article.Key Words: Electrochemical spectroscopy; Fourier transform infrared spectroscopy;Surface enhanced Raman spectroscopy; Sum-frequency generation spectroscopy电化学谱学表征方法的应用与发展朱越洲1，王琨1，郑世胜2,*，汪弘嘉1，董金超1，李剑锋1,*1厦门大学化学化工学院，固体表面物理化学国家重点实验室，福建厦门 3610052北京大学深圳研究生院，新材料学院，广东深圳 518000摘要：经历两个多世纪的发展，电化学表征方法的理论和实验研究不断完善，在表界面精细结构表征、电化学反应机理研究等方面起到重要作用。

中空碳球的制备及其在甲醇燃料电波中的应用论文

摘要摘要中空碳球（HCS）作为一种新型甲醇燃料电池的电催化剂载体，由于其结构可控、密度低、比表面积高和电催化性能良好等性质，受到了国内外科学工作者的广泛关注。

模板法作为一种简单的制备可控形状物质的方法，开辟了制备中空碳球的一个全新领域。

本论文分别以二氧化硅和聚苯乙烯作为核模板合成中空碳球，同时将Pt纳米粒子催化剂包裹在中空碳球的内部，使中空碳球功能化，合成Pt纳米粒子催化剂核/中空碳壳（Pt@C）微球，并研究了将其用于甲醇燃料电池电极的催化性能。

主要研究工作如下：1．以二氧化硅为核模板，酚醛树脂为碳源，分别采用聚乙烯吡咯烷酮（PVP）、十六烷基三甲基溴化铵（CTAB）和3-氨丙基三乙氧基硅烷（APTS）对二氧化硅表面进行功能化修饰，合成中空碳球，并通过控制酸催化缩聚反应的作用点，得到了不同形貌的碳材料。

用SEM、FT-IR和TGA对所制材料进行了表征。

研究结果证明，修饰剂的选择对中空碳球的形貌和稳定性具有很大的影响，APTS作为二氧化硅表面修饰剂，通过氢键与酚醛树脂结合，因此所形成的中空碳球的球形结构和稳定性最好。

此外，不同的酸催化活性点对碳材料表面形态也有很大影响。

通过改变酸催化缩聚反应的作用点，可以得到单一分散的中空碳球和有序排列的多孔碳材料。

2．以磺化聚苯乙烯球为模板，苯胺为碳源，制备中空碳球。

采用SEM、TEM、XRD、FT-IR、TGA和CV对所制的样品进行了表征。

研究结果表明，制备的中空碳球壁厚为35nm 且粒径均匀，中空碳球的形貌和壳层厚度受聚苯乙烯模板磺化度的影响。

对聚苯乙烯球表面进行磺酸化8h是制备中空碳球最合适的模板。

CV研究结果表明，将所制备的中空碳球（HCS）用作催化剂载体，合成Pt/HCS催化剂在甲醇电化学氧化中表现出较Pt/C催化剂更高的催化性能，其甲醇电化学氧化峰电流密度比Pt/C催化剂高了1.86倍。

3．采用模板法制备了铂纳米核/中空碳壳（Pt@C）微球,作为一种新颖的催化剂，将其应用于甲醇燃料电池催化剂，并用XRD、SEM-EDS、TEM、TGA、N2吸附和CV等手段对材料的催化剂粒径、负载情况及催化性能进行了表征。

电催化剂英语

电催化剂英语Electrochemical Catalysts: Revolutionizing Energy Conversion and StorageElectrochemical catalysts have emerged as a critical component in the global pursuit of sustainable energy solutions. These remarkable materials have the ability to accelerate chemical reactions, enabling more efficient and cost-effective energy conversion and storage technologies. From fuel cells to metal-air batteries, electrochemical catalysts have the potential to transform the way we harness and utilize energy, paving the way for a cleaner and more sustainable future.At the heart of electrochemical catalysis lies the intricate interplay between the catalyst's structure, composition, and the electrochemical reactions it facilitates. Catalysts can be designed to target specific reactions, optimizing their performance and selectivity. This tailored approach allows for the development of highly efficient systems that can overcome the limitations of traditional energy technologies.One of the primary applications of electrochemical catalysts is in fuelcells. Fuel cells are electrochemical devices that convert the chemical energy of fuels, such as hydrogen or methanol, directly into electrical energy. The efficiency of fuel cells is largely dependent on the performance of the catalysts used in the electrochemical reactions. Platinum-based catalysts have been widely used in fuel cell technology, but their high cost and limited availability have driven the search for alternative, more cost-effective catalysts.Researchers have explored a wide range of non-precious metal catalysts, such as transition metal oxides, nitrides, and sulfides, as well as carbon-based materials, to address the cost and scarcity issues associated with platinum. These alternative catalysts have shown promising performance, often matching or even exceeding the activity and durability of their platinum-based counterparts. The development of these cost-effective and earth-abundant catalysts has the potential to significantly improve the commercialization and widespread adoption of fuel cell technology.Another crucial application of electrochemical catalysts is in metal-air batteries, which have gained attention due to their high energy density and potential for low-cost energy storage. In these batteries, the electrochemical reactions at the air cathode are catalyzed by specific materials, enabling efficient oxygen reduction and oxygen evolution. The performance of these catalysts directly impacts the battery's energy efficiency, cycle life, and overall viability as anenergy storage solution.Researchers have explored a variety of catalyst materials for metal-air batteries, including transition metal oxides, perovskites, and carbon-based materials. These catalysts have shown improved activity, stability, and selectivity, addressing the challenges associated with traditional metal-air battery technologies. The development of advanced electrochemical catalysts has the potential to unlock the full potential of metal-air batteries, making them a more attractive option for large-scale energy storage applications.Beyond fuel cells and metal-air batteries, electrochemical catalysts play a crucial role in other energy conversion and storage technologies, such as water electrolysis and metal-ion batteries. In water electrolysis, catalysts are used to facilitate the splitting of water molecules into hydrogen and oxygen, enabling the production of clean hydrogen fuel. Similarly, in metal-ion batteries, electrochemical catalysts can enhance the efficiency of the redox reactions, leading to improved energy density and cycle life.The versatility of electrochemical catalysts extends beyond energy applications. These materials also find use in environmental remediation, such as the electrochemical treatment of wastewater and the removal of pollutants. Catalysts can be designed to selectively target and degrade various contaminants, making themvaluable tools in the quest for sustainable and eco-friendly solutions.The development of advanced electrochemical catalysts is an ongoing and dynamic field of research, with scientists and engineers continuously exploring new materials, structures, and synthesis methods to enhance their performance and cost-effectiveness. Computational modeling and machine learning techniques have played a crucial role in accelerating the discovery and optimization of novel catalyst materials, enabling rapid progress in this field.As the global demand for clean and efficient energy solutions continues to grow, the importance of electrochemical catalysts cannot be overstated. These remarkable materials hold the key to unlocking the full potential of energy conversion and storage technologies, paving the way for a more sustainable and environmentally-conscious future. Through continued research and innovation, electrochemical catalysts will undoubtedly play a pivotal role in shaping the energy landscape of tomorrow.。

CoNi2S4上电沉积NiS用于柔性固态非对称超级电容器

收稿日期：2020⁃07⁃23。

收修改稿日期：2020⁃11⁃09。

国家重点研发项目(No.2018YFB2001204)资助。

＊通信联系人。

E⁃mail ：*******************，**********************.cn第37卷第1期2021年1月Vol.37No.1171⁃179无机化学学报CHINESE JOURNAL OF INORGANIC CHEMISTRYCoNi 2S 4上电沉积NiS 用于柔性固态非对称超级电容器何业增＊,1赵后强1柳朋1隋艳伟1委福祥1戚继球1孟庆坤1任耀剑1庄栋栋＊,2(1中国矿业大学材料与物理学院，徐州221116)(2江苏大学材料科学与工程学院，镇江212013)摘要：采用一种在CoNi 2S 4上电沉积NiS 的有效方法来改善钴/镍硫化物的性能。

CoNi 2S 4@NiS 电极材料在1A·g -1时比电容达到1433F·g -1，并具有很好的倍率性能。

CoNi 2S 4@NiS 和还原氧化石墨烯组装成的柔性固态非对称超级电容器的能量密度在功率密度为800W·kg -1时达到36.6Wh·kg -1，并且在10000次充放电后表现出良好的循环性能，循环保持率达87.8%。

关键词：电化学；超级电容器；设计合成；CoNi 2S 4；NiS ；电沉积；固态中图分类号：O614.81+3；O614.81+2文献标识码：A文章编号：1001⁃4861(2021)01⁃0171⁃09DOI ：10.11862/CJIC.2021.011Electrodeposition of NiS on CoNi 2S 4for Flexible Solid⁃State Asymmetric SupercapacitorsHE Ye⁃Zeng ＊,1ZHAO Hou⁃Qiang 1LIU Peng 1SUI Yan⁃Wei 1WEI Fu⁃Xiang 1QI Ji⁃Qiu 1MENG Qing⁃Kun 1REN Yao⁃Jian 1ZHUANG Dong⁃Dong ＊,2(1School of Materials and Physics,China University of Mining and Technology,Xuzhou,Jiangsu 221116,China )(2School of Material Science and Engineering,Jiangsu University,Zhenjiang,Jiangsu 212013,China )Abstract:An effective approach of depositing NiS on CoNi 2S 4was adopted to improve the performance of bimetalliccobalt/nickel⁃sulfide.The as⁃obtained CoNi 2S 4@NiS had an excellent specific capacitance of 1433F·g -1at 1A·g -1and shows a superior rate performance of 69.6%at 10A·g -1.A flexible solid ⁃state asymmetric supercapacitorassembled with CoNi 2S 4@NiS and the reduced graphene oxide showed a high energy density of 36.6Wh·kg -1at a power density of 800W·kg -1and had a fantastic cycle performance of 78.7%retention after 10000cycles,indicat⁃ing that the CoNi 2S 4@NiS nanocomposite is a promising electrode material for energy storage devices.Keywords:electrochemistry;supercapacitor;synthesis design;CoNi 2S 4;NiS;electrodeposition;solid⁃state0IntroductionWith the development of science and technology,the increasing demands of high efficiency energy stor⁃age units in modern electronics are becoming more salient [1⁃4].In the last few years,the supercapacitor hasbecome one of the promising effective and practical energy storage devices for its high power density,goodcycle stability and fast charging rate [5⁃7].The perfor⁃mance and application of supercapacitors are mainly determined by the electrode materials.Therefore,improving the performance of the electrode materials has become a hotspot in the field of energy storage [8⁃9].Transition metal sulfide,a new type of electrodematerial,has been extensively researched due to its su⁃perior electrochemical performance [10⁃12].Among all sul⁃无机化学学报第37卷fides,CoNi2S4has received increasing attention be⁃cause of the synergistic effect of nickel sulfide and co⁃baltous sulfide[13⁃16].Compared with the oxidation prod⁃ucts(CoNi2O4),the extension of chemical bonds inCoNi2S4is beneficial to form a more flexible structureand makes it easier for ion transport[17⁃20].However,therapid decay of specific capacitance during the charge⁃discharge cycles restricts the further application inenergy storage[21⁃24].To overcome this shortcoming,de⁃veloping composite materials has been proven to be themost efficient way and has been widely used in thepreparation of the electrode materials[25⁃26].It has beenreported that the hierarchical CoNi2S4@CC nanowire issuccessfully designed and synthesized by the hydro⁃thermal process,which shows excellent specific capaci⁃tance(1872F·g-1at1A·g-1),fantastic rate capabilityand superior cycling stability when utilized as the elec⁃trode material of supercapacitors[27].Furthermore,Co0.85Se@CoNi2S4/GF(graphene foam)nanotubes,applied to the electrode material of supercapacitors,are successfully prepared by a concise one⁃step electro⁃chemical method,which have excellent interface effectand hollow structure and show outstanding specificcapacitance of5.25F·cm-2at1mA·cm-2,remarkablecharge storage capacity and superior rate perfor⁃mance[28].In this work,CoNi2S4@NiS nanocomposites weresuccessfully synthesized by combining the hydrother⁃mal and electrodeposition methods.The synthesizedCoNi2S4@NiS electrode showed an excellent perfor⁃mance of1433F·g-1at1A·g-1,which is superior tothe CoNi2S4and NiS electrodes.Moreover,a flexiblesolid⁃state asymmetric supercapacitor CoNi2S4@NiS//rGO was assembled by CoNi2S4@NiS and reduced gra⁃phene oxide(rGO),which exhibits an outstanding elec⁃trochemical performance and has promising potentialfor application in supercapacitors.1Experimental1.1Synthesis of CoNi2S4on carbon fiber cloth(CoNi2S4@CC)The carbon fiber cloth(CC,1.0cm×2.0cm)was ultrasonically cleaned with0.5mol·L-1KMnO4for30min individually and then was washed with ethanol and deionized water for several times and desiccated in a vacuum oven at70℃for12h.The CoNi2S4was pre⁃pared by a hydrothermal reaction.0.291g Co(NO3)2·6H2O,0.237g NiCl2·6H2O,0.060g CO(NH2)2and 0.300g thioacetamide(TAA)were used as sources, respectively.Under the continuous magnetic stirring for30min,the above reagents were immersed in30 mL deionized water to get a uniform solution.Subse⁃quently,the uniform solution was transferred into50 mL Teflon⁃lined autoclave and the treated CC was immersed into the solution,then the autoclave was heated at180℃for24h.The final product was ultra⁃sonically rinsed with deionized water and ethanol, respectively.After dried at70℃for12h,the product was denoted as CoNi2S4@CC.1.2Synthesis of CoNi2S4@NiSThe NiS was synthesized by facile and effective three⁃electrode system electrodeposition.2.376g NiCl2·6H2O and7.612g CH4N2S were mixed in100 mL deionized water and stirred for30min to obtain a homogenous solution.Then,the electrodeposition pro⁃cess was conducted for5min at an invariable voltage of0.9V,while the CoNi2S4@CC was served as the work electrode.After that,the samples were washed with eth⁃anol and deionized water separately,and the products were dried in a vacuum environment at70℃.For com⁃parison,the pure NiS without CoNi2S4was also synthe⁃sized on the CC under the same procedure.1.3CharacterizationThe crystalline and structural of the synthesized samples were examined by X⁃ray diffraction(XRD) using Bruker D8Advance diffractometer with Cu Kαradiation(0.154nm)at40kV and30mA,and at a scan rate of6(°)·min-1in the2θrange from10°to80°. The microstructure of the samples was investigated using scanning microscopy(SEM)at5kV,transmis⁃sion electron microscopy(TEM)with an accelerating voltage of200kV,high⁃resolution transmission elec⁃tron microscopy(HRTEM)and selected area electron diffraction(SAED).X⁃ray photoelectron spectroscopy (XPS,1486.7eV)was used to observe the elemental analysis and chemical valence state of the lased irradi⁃172第1期ated samples.1.4Electrochemical measurementsThe electrochemical performance of the samplewas measured on an electrochemical workstation(CHI660E).Cyclic voltammetry (CV),galvanostaticcharge/discharge (GCD)and electrochemical imped⁃ance spectroscopy (EIS)were conducted as the mainpaths to exhibit the electrochemical behaviors.The electrochemical test was proceeded in a three⁃electro configuration in 2mol·L -1KOH electrolyte and the positive and the negative electrode were the as⁃sample and the Pt,the Hg/HgO serve as the reference elec⁃trode,respectively.The specific capacitance can be calculated from the GCD curves by the following equa⁃tion (1):C A =I Δtm ΔV(1)Where I (A)represents discharge current,m (g)repre⁃sents the accurate weight of the active material,Δt (s)represents the discharge time,and ΔV represents the potential window,respectively.1.5Fabrication and electrochemical measure⁃ments of asymmetric supercapacitorThe all⁃solid⁃state asymmetric hybrid supercapac⁃itor (ASC)device was assembled by using the CoNi 2S 4@CC as the positive electrode and rGO as the negativeelectrode,while the PVA⁃KOH gel (PVA=polyvinyl al⁃cohol)performed as the electrolyte.The positive andnegative electrode were dissolved in the PVA⁃KOH gel solution,then two electrodes were combined at roomtemperature and dry until the electrolyte is completely cured,and the solid⁃state supercapacitor was prepared.So as to obtain an ASC with excellent electrochemical properties,it is required to balance the relationship (q +=q -)of the two electrodes charge.As the stored charge of the electrode,the q can be calculated by theequation (2):q =Cm ΔV(2)where C (F·g -1)represents the specific capacitance,m(g)is the mass of the active material and ΔV (V)is the potential window.Meanwhile,the ideal mass ratio canbe calculated by the equation (3):m +m -=C -ΔV -C +ΔV +(3)Where,C +(F·g -1)and C -(F·g -1)represent the specificcapacitance of CoNi 2S 4@NiS and rGO electrode.ΔV +(V)and ΔV -(V)represent the voltage range of CoNi 2S 4@NiS and rGO electrode,respectively.The power den⁃sity (P ,W·kg -1)and the energy density (E ,Wh·kg -1)of CoNi 2S 4@NiS//rGO ASC device can be calculated bythe equations (4,5):E =12C (ΔV )2(4)P =E Δt(5)Where Δt (s)is the discharge time,ΔV (V)is the volt⁃age range and C (F·g -1)is the specific capacitance ofCoNi 2S 4@NiS//rGO ASC device.2Result and discussions2.1Structural and morphological characteriza⁃tionThe XRD patterns of NiS,CoNi 2S 4@CC and CoNi 2S 4@NiS composite are illustrated in Fig.1.TheXRD pattern of the NiS had the same diffraction peakswith the CoNi 2S 4@NiS at 2θ=30.31°,34.77°,46.08°and 53.58°,which can be attributed to the (100),(101),(102)and (110)planes of the NiS (PDF No.75⁃0613).The patterns of the CoNi 2S 4@CC and CoNi 2S 4@NiSshow the same peaks at 2θ=16.28°,26.82°,31.52°,38.30°,47.33°,50.29°and 55.22°,which are indexed to the (111),(220),(311),(400),(422),(511)and (440)planes of the CoNi 2S 4(PDF No.24⁃0334),respectively.In addition,the XRD patterns of the threesamples Fig.1XRD patterns of the NiS,CoNi 2S 4@CC and CoNi 2S 4@NiS何业增等：CoNi 2S 4上电沉积NiS 用于柔性固态非对称超级电容器173无机化学学报第37卷exhibited the extra diffraction peak at2θ=26°,which can be contributed to the carbon fiber cloth substrate (PDF No.26⁃1080).Moreover,there were no other im⁃purity peaks on the patterns,indicating that the suc⁃cessful synthesis of CoNi2S4@NiS on the carbon fiber cloth.The surface element analysis and chemical valence state of the CoNi2S4@NiS sample were further confirmed by XPS as plotted in Fig.2.Fig.2a exhibited the survey spectrum and revealed the presence of Ni, Co,S and C elements in the multiple materials.The Co2p XPS spectrum of the CoNi2S4@NiS is shown in Fig.2b.The peaks situated at779.78and795.15eV are attributed to the Co2p3/2and Co2p1/2levels of Co2+. The peaks situated at778.55and793.33eV reveal the Co2p3/2and Co2p1/2levels of Co3+.It proves that the coexistence of Co2+and Co3+in the CoNi2S4@NiS composite[29].The Ni2p spectrum is shown in Fig.2c, the diffraction peaks situated at853.45and872.38eV are attributed to Ni2+and the peak at856.16and 876.21eV are related to Ni3+[30].The S2p spectrum is displayed in Fig.2d,the diffraction peaks located at 162.98and161.68eV can be assigned to S2p1/2and S2p3/2[18].Moreover,the peak at169.13eV indicates that the existence of S⁃O[31].The morphology of NiS,CoNi2S4/CC and CoNi2S4 @NiS electrode materials can be observed in SEM im⁃ages(Fig.3).As exhibited in Fig.3a and3b,the Co⁃Ni2S4@CC presented a hexagonal flaky cubic structure and were tightly attached to the CC.Fig.3c and3d ex⁃hibit the morphology of the NiS,which presented a granular structure with a size of about50~200nm. These cross⁃linked nanoparticles would provide a high⁃er electrode/electrolyte active sites for reaction and a shorter ion diffusion way[32⁃33].The microstructure of the CoNi2S4@NiS is shown in Fig.3e and3f,the NiS nanoparticles were anchored onto the surface of Co⁃Ni2S4@NiS and form a dense film.The unique structure provides a large specific surface area,which enhance the active sites and would effectively enhance the spe⁃cific capacitance of composite materials.To better understand the chemical compositeand Fig.2(a)XPS survey spectrum of CoNi2S4@NiS;(b~d)XPS spectra of Co2p,Ni2p and S2p174第1期detailed structures of the synthesized CoNi2S4@NiS, HRTEM and element mapping analyses were conduct⁃ed.The HRTEM images of the CoNi2S4@NiS are shown in Fig.4a and4b.The interplanar spacing can be mea⁃sured to be0.20and0.28nm,which can be ascribe to the(102)lattice plane of NiS and(311)lattice plane of CoNi2S4,respectively.The consequences are match with the XRD and XPS tests.Fig.4c and4f displays the elemental mappings of the Co,Ni,Co/Ni and S in the CoNi2S4@NiS samples.The distribution area of the Ni element was slightly larger than the Co element.The Ni and Co element coexisted in the central regionof Fig.3SEM images of(a,b)CoNi2S4@CC,(c,d)NiS and(e,f)CoNi2S4@NiSFig.4(a,b)TEM images of CoNi2S4@NiS;(c~f)Element mappings of the Co,Ni,Co/Ni and S何业增等：CoNi2S4上电沉积NiS用于柔性固态非对称超级电容器175无机化学学报第37卷the sample,while in the outside of the sample there is only Ni element left.In consideration of that CoNi2S4 contained Ni and Co element while NiS had no Co ele⁃ment,it can be deduced that the outer layer of the com⁃posite is NiS which wraps the inner CoNi2S4.2.2Electrochemical performanceThe electrochemical performance of CoNi2S4@CC, NiS,and CoNi2S4@NiS electrodes were tested on a three ⁃electrode configuration with2mol·L-1KOH electro⁃lyte.Fig.5a shows the CV curves for CoNi2S4@CC,NiS, and CoNi2S4@NiS electrodes measured at a scan rate of 10mV·s-1.The CoNi2S4@NiS exhibited superior specif⁃ic capacitance and the redox peaks can be regard as the symbol of Faradaic feature.The improvement of the specific capacitance of the CoNi2S4@NiS is mainly con⁃tributed to the fact that the elements in the two sub⁃stances have multiple valence states,which can carry out the redox reaction more effectively[34].The CV curves of CoNi2S4@NiS electrode at different scan rates from10to50mV·s-1are shown in Fig.5b.The trend of the CV curves was basically maintained with the scan rate increasing,indicating the CoNi2S4@NiS electrode possess ideal pseudocapacitance characteristic and superior rate performance.The large deviation of the shape in large scan rate can be explained by the mis⁃match between charge transfer and diffusion.It can be observed that the cathode peak moved to a lower poten⁃tial,and meanwhile,the anode peak moved to ahigherFig.5Electrochemical performance of CoNi2S4,NiS and CoNi2S4@NiS:(a)CV curves of the CoNi2S4,NiS and CoNi2S4@NiS samples at a scan rate of10mV·s-1;(b)CV curves of the CoNi2S4@NiS sample at various scan rates;(c)GCD curvesof the CoNi2S4CC,NiS and CoNi2S4@NiS samples at a current density of1A·g-1;(d)GCD curves of the CoNi2S4@NiSat various current densities;(e)Comparison of specific capacitance;(f)EIS Nyquist plots of the CoNi2S4,NiS andCoNi2S4@NiS samples176第1期potential when the scan rate continued to increase, which can be explained by the polarization in different scan rates[35].As displayed in Fig.5c,the GCD curves of CoNi2S4@CC,NiS,and CoNi2S4@NiS electrode were measured at a current density of1A·g-1to confirm the advantage of the CoNi2S4@NiS.The discharge time of CoNi2S4@NiS was larger than NiS and CoNi2S4@CC, suggesting the composite structure is conducive to en⁃hance the specific paring to the NiS (1245F·g-1at1A·g-1)and CoNi2S4/CC(1165F·g-1 at1A·g-1),CoNi2S4@NiS(1433F·g-1at1A·g-1)ex⁃hibited higher specific capacitances.Fig.5d illustrates the GCD curves of CoNi2S4@NiS at different current densities to further investigate charge and discharge mechanism.It can be found that the curves show an apparent voltage platform,which is characteristic of typical pseudocapacitor behavior.The result can sup⁃plement the above conclusion.Moreover,the nonlinear curves of the GCD maintained the similarity and sym⁃metry indicating the good stability.The specific capaci⁃tances of NiS,CoNi2S4@CC and CoNi2S4@NiS calculat⁃ed are illustrated in Fig.5e.The specific capacitances of CoNi2S4@NiS were1433,1284,1248,1170,1073 and998F·g-1at1,2,3,5,8and10A·g-1,which possess better rate stability compared with the NiS and CoNi2S4@CC.The electrode cannot fully participate in the reaction when the current density increases,and the utilization rate of the electrochemically active mate⁃rial is insufficient,so the specific capacitance will decrease at a higher current density.As is shown in Fig.5f,the EIS curve of CoNi2S4@CC,NiS,and CoNi2S4 @NiS were fitted using the equivalent circuit model, where CPE is the constant phase angle original and Z W is the Warburg resistance.The equivalent series resis⁃tance(R s)value of NiS,CoNi2S4@CC and CoNi2S4@NiS were1.12,1.56and1.01Ω,indicating that the CoNi2S4 @CC electrode had the lowest internal impedance. Moreover,the value of charge transfer resistance(R ct) can be fitted to be0.25,1.62and0.56Ωfor the NiS, CoNi2S4@CC and CoNi2S4@NiS,suggesting that the CoNi2S4@CC electrode had much large R ct than that of the NiS and CoNi2S4@NiS electrode.Besides,the slope of the samples was greater than45°in the low frequen⁃cy region,indicating the ions and electrolyte are effec⁃tively diffused in the entire system,resulting in a re⁃duction in the diffusion resistance of the NiS,Co⁃Ni2S4@CC and CoNi2S4@NiS electrodes[36].A flexible solid⁃state asymmetric supercapacitor (ASC)device(CoNi2S4@NiS//rGO)was assembled to confirm the energy storage properties for practical ap⁃plication.Fig.6a is the CV curves of the CoNi2S4@NiS and rGO electrode under the three⁃electrode configura⁃tion at the scan rate of10mV·s-1.Obviously,the poten⁃tial windows of the positive and negative electrode were connected,indicating that the loss of potential is nonexistent.The CV curves of CoNi2S4@NiS//rGO at different scan rates(10~100mV·s-1)are displayed in Fig.6b.Significantly,the curves maintained the similar trend with the scan rate increase,and the polarization phenomenon was minimal even at the scan rate of100 mV·s-1,suggesting the device has excellent electro⁃chemical reversibility.Fig.6c exhibits the GCD curves of CoNi2S4@NiS//rGO at different current densities, which possessed good symmetry and had no obvious electrochemical reaction platform.Fig.6d exhibits an excellent specific capacitance of the CoNi2S4@NiS// rGO ASC(103.43F·g-1at1A·g-1and maintained 61.25F·g-1at10A·g-1),revealing excellent rate capa⁃bility.The EIS of the CoNi2S4@NiS//rGO ASC device is shown in Fig.6e.In the high⁃frequency region,the R s and R ct can be calculated to be1.019and4.89Ω.Fur⁃thermore,cycling performance is also a significant indi⁃cator to evaluate the practical application of superca⁃pacitor electrode materials.Fig.6f exhibits a superior cycle performance,which maintained78.7%after 10000cycles at10A·g-1.The superiority of specific capacitance and capacitance retention may be contrib⁃uted to the special nanostructure.The unique structure can provide large space for reaction between electrode and electrolyte by large interface which may supply more active sites.The energy and power density calculated to evalu⁃ated the properties of the CoNi2S4@NiS//rGO ASC device.Fig.7exhibits the Ragone plot of the CoNi2S4 @NiS//rGO ASC.The CoNi2S4@NiS//rGO ASC device exhibited a high energy density of36.6Wh·kg-1at800何业增等：CoNi2S4上电沉积NiS用于柔性固态非对称超级电容器177无机化学学报第37卷W·kg -1and the energy density maintained 21.7Wh·kg -1even at 8000W·kg -1.The CoNi 2S 4@NiS//rGOASC device have an advantage over some other report⁃ed devices,such as CoNi 2S 4//YS⁃CS (yolk⁃shell carbonspheres)(35Wh·kg -1at 640W·kg -1),Ni 3S 2/MWCNT(multiwalled carbon nanotube)⁃NC//AC (19.8Wh·kg -1at 798W·kg -1),NiCo 2S 4//rGO (16.6Wh·kg -1at 2348W·kg -1)and NiS/rGO//AC (18.7Wh·kg -1at 1240W·kg -1)[37⁃40].3ConclusionsIn conclusion,the CoNi 2S 4@NiS was successfullysynthesized by combining the hydrothermal and elec⁃trodeposition methods.The as⁃obtained samples exhib⁃ited an excellent specific capacitance (1433F·g -1at 1A·g -1)and superior rate performance (998F·g -1at 10A·g -1).The flexible solid⁃state asymmetricsupercapac⁃Fig.7Ragone plot of the ASC deviceFig.6Electrochemical measurements of the resultant CoNi 2S 4@NiS//rGO:(a)CV curves of the resultant CoNi 2S 4@NiSand rGO at 10mV·s -1;(b)CV curves of the device at different current densities;(c)GCD curves of the ASC device;(d)Specific capacitance at various current densities;(e)EIS Nyquist plots of the device;(f)Cycling performance ofthe device at 10A·g -1for 10000cycles178第1期itor assembled with CoNi2S4as the positive electrode and the reduced rGO as the negative electrode showed superior energy density of36.6Wh·kg-1at a power density of800W·kg-1,remarkable rate performance, and excellent cycle performance(78.7%at a high current density of10A·g-1after10000cycles).The results 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导电聚合物超级电容器电极材料_涂亮亮

第22卷第8期2010年8月化学进展PROGRESS IN CHEMISTRYVol.22No.8Aug.，2010收稿：2009年10月，收修改稿：2009年12月*国家自然科学基金项目（No.20602005，20873015）、四川省科技厅科技支撑项目（No.2009FZ0230）和电子科技大学青年基金重点项目（No.JX0671）资助 Corresponding authore-mail ：cyjia@导电聚合物超级电容器电极材料*涂亮亮贾春阳（电子科技大学电子薄膜与集成器件国家重点实验室微电子与固体电子学院成都610054）摘要导电聚合物（聚苯胺、聚吡咯、聚噻吩）作为超级电容器电极材料的研究引起了人们广泛的兴趣，该类材料制备的超级电容器具有成本低、容量高、充放电时间短、环境友好和安全性高等优点。

本文综述了近年来基于导电聚合物及其与无机材料（碳材料/金属氧化物材料）复合所得电极材料在超级电容器中的应用进展，指出具有纳米结构导电聚合物材料及导电聚合物与无机纳米材料的复合是超级电容器电极材料研究的重要发展方向。

关键词导电聚合物超级电容器纳米结构复合材料中图分类号：O631；TB34文献标识码：A文章编号：1005-281X （2010）08-1610-09Conducting Polymers as Electrode Materials for SupercapacitorsTu LiangliangJia Chunyang（State Key Laboratory of Electronic Thin Films and Integrated Devices ，School of Microelectronics and Solid-State Electronics ，University of Electronic Science and Technology of China ，Chengdu 610054，China ）AbstractConducting polymers （polyaniline ，polypyrrole and polythiophene ）as electrode materials forsupercapacitor have been attracted great interest due to their low cost ，high capacity ，rapid charge and discharge ，environmental friendliness and safety.In this paper ，conducting polymers and hybrid materials of conducting polymers and inorganic materials （carbon materials /metal oxide materials ）as electrode materials for supercapacitor have been reviewed ，it is believed that the conducting polymers with nanostructures and the hybrid materials of conducting polymers and inorganic nanomaterials are the important research directions of electrode materials for supercapacitor.Key wordsconducting polymers ；supercapacitor ；nanostructure ；hybrid materialsContents1Introduction2The mechanism of storge energy of supercapacitor 3Electrode materials of supercapacitor based on polyaniline4Electrode materials of supercapacitor based on polypyrrole5Electrode materials of supercapacitor based onpolythiophene 6Electrode materials of supercapacitor based on hybrid materials 7Conclusion and outlook1引言电化学超级电容器［1，2］（electrochemicalsupercapacitors ，ES ）也叫超级电容器（supercapacitors ），是介于电池和传统电容器之间、第8期涂亮亮等导电聚合物超级电容器电极材料·1611·能快速充放电、基于电极/溶液界面电化学过程的储能元件。

湿法制备纳米二氧化锰及其电化学性能的研究_常照荣

第34卷　第1期河南师范大学学报(自然科学版)V ol.34　N o.1　2006年2月J ournal o f H enan N or mal U nivers ity(N atural S cience)Feb.2006 文章编号:1000-2367(2006)01-0077-05湿法制备纳米二氧化锰及其电化学性能的研究常照荣,刘院英,汤宏伟,李云平(河南师范大学化学环境与科学学院,河南新乡453007)摘　要:分别用氧化法、还原法和氧化还原法在溶液中反应制备了M nO2粉末.用X射线衍射(X RD)、扫描电子显微镜(SEM)、循环伏安、交流阻抗、恒电流充放电等测试方法对3种样品结构、形貌和电化学性能进行分析比较.研究表明:三样品均为无定型M nO2,形貌呈团聚的球形,其中用氧化法制备的M nO2具有良好的电容性能和放电容量.关键词:超级电容器;锂离子电池;M nO2电极;电极材料中图分类号:O646 文献标识码:A二氧化锰作为活性物质一般广泛用于锌锰以及高性能碱锰电池中,最近几年作为锂离子电池[1～3]和电容器[4～5]的电极活性材料的研究也取得了一定的进展.二氧化锰的晶体结构和存在状态,对其电化学性能起着决定性作用.不同的合成方法可以得到不同形式的产品,直接影响着二氧化锰的电化学性能.自然界中二氧化锰资源并不缺乏,但是天然二氧化锰的纯度不高,并且天然二氧化锰的提纯工艺相当繁琐,不能直接作为电极活性材料.电解二氧化锰虽然电化学性能优异,但是成本高,耗电多,投资大,并且颗粒较大.因此选择适宜的合成方法制备综合性能较好,尤其是能够作为锂离子电池和电容器电极材料的二氧化锰仍具有较大的意义.根据制备化学二氧化锰的环境不同,可以分为湿法制备和固相法制备两种.本文用湿法制备了3种化学二氧化锰,初步研究了它们的电容行为和在锂离子电池中的放电性能,并对其性能进行了比较.1　实验部分1.1　材料的制备1.1.1　氧化法制备纳米M nO2在室温以一定速度搅拌下,将一定量的1mol/L的M nCl2(A.R)溶液加入给定体积的NaOH和NaOCl 混和溶液中(摩尔比:NaOH∶M nCl2=2.5;NaOCl∶MnCl2=1.15),搅拌2h,静止24h,用去离子水反复冲洗,直到洗液为无色,然后抽滤,在100℃下干燥、于玛瑙研钵中研磨得到A样品.1.1.2　还原法制备纳米M nO2在75℃以一定搅拌速度下,将适量1mol/L盐酸以一定流速加入到一定体积的0.12mol/L的KM nO4 (A.R)溶液中,搅拌2h,静止24h,用去离子水反复冲洗,直到洗液为无色,然后抽滤,在100℃下烘干、研磨得B样品.1.1.3　氧化还原法制备纳米M nO2在75℃以一定速度搅拌下,将适量的0.12m ol/L的KM nO4(A.R)以一定的速度加入到1mol/L的MnCl2(A.R)溶液中(摩尔比:M n7+∶M n2+=2∶3),搅拌2h,充分反应后,用去离子水反复冲洗,直到洗收稿日期:2005-04-26 基金项目:国家自然科学基金资助项目(90206043) 作者简介:常照荣(1956-),男,河南新乡人,河南师范大学教授,主要从事电池正极材料和应用电化学领域的研究.78河南师范大学学报(自然科学版) 2006年液呈中性(用pH试纸测定),然后抽滤,在100℃下烘干、研磨得C样品.1.2　试样的物性测试用德国Bruker ax s D8型X-射线衍射仪对试样进行测试,采用Cukα辐射,波长1.4506×10-8cm,单晶硅为内标.工作电压为40kV,工作电流为40m A,扫描速度0.02o/s,扫描角度范围10o～70o.用美国的AMA RY-1000B扫描电子显微镜对试样进行形貌观察.1.3　电极的制备和电性能测试将制得的M nO2粉体与乙炔黑、聚四氟乙烯按60∶30∶10的质量比混合,在20Mpa的压力下将电极材料压在泡沫镍上面.A,B,C三试样制作的工作电极分别标为a,b,c电极,其面积为2cm×2cm,辅助电极采用2cm×2cm的镍网,参比电极为Hg/H gO电极.循环伏安、交流阻抗和恒电流充放电测试在上海辰华仪器公司CH I660A电化学工作站上进行.插锂实验用的电极制备是将上述混合物在20Mpa的压力下压在镍网上,电极的直径为1cm,锂片作为辅助电极,直径也为1cm,电解液采用LiPF6+PC/DM E溶液.用A,B,C三种试样制作的电极分别标为a, b,c电极.测试在DC-5BAT TERY TESTING INST RUM ENT上进行.2　结果与讨论2.1　材料的物性试样制备的反应方程式分别是:氧化法:M nCl2+NaOCl+2NaOH=MnO2+3NaCl+H2O还原法:2KMnO4+8H Cl=2MnO2+4H2O+3Cl2+2KCl氧化还原法:2KM nO4+3M nC l2+2H2O=5MnO2+4H Cl+2KCl实验发现:3种方法所制备的二氧化锰的表观颜色不同,氧化法制备的M nO2是棕色的粉体,而还原法和氧化还原法制备的MnO2的是黑色粉体.这可能是由于3种制备M nO2的反应所处的化学环境不同所致.氧化法制备M nO2是在碱性环境中进行,而还原法和氧化还原法制备的MnO2是在酸性环境中进行(盐酸为反应物或产物).实验表明:在酸性环境中制备的MnO2呈黑色的粉体,在碱性环境中制备的M nO2为棕色的粉体.为了进一步的证明,将氧化还原法制备的MnO2浑浊液分为3份:一份浑浊液冷却静止、抽滤;另2份浑浊液分别滴加8m ol/L的氨水和1mo l/L的NaOH溶液,直到溶液呈碱性﹙用pH试纸测试﹚,然后冷却、静止、抽滤.结果所得产物前者为黑色,后2份为棕色的M nO2粉体.可见产物的颜色与反应所处的酸碱性有直接关系.3种方法制备的M nO2其晶体结构和形貌见图1和图2.由图1可见:采用3种方法制备的M nO2粉体均没有明显的特征衍射峰,属于无定形结构.但从图2的SEM照片上看,3种方法制备的M nO2形貌均为球形,并且其粒径为纳米级尺寸,这可能是无定形粉末在溶液中的团聚所至.从图上可以看出:A样呈规则、均匀、分散的球状物;B样为规则、不均匀、团聚的球状物;C样为不规则、均匀、分散的球状物.2.2　电化学性能的测试2.2.1　循环伏安测试分别将制作好的a,b,c三电极在1mol/L的KOH水溶液中做循环伏安测试,循环伏安测试的扫描速度是1mV/s.由图3可见:在(-0.1～0.6)V电压范围内,a,b,c三电极均表现出法拉第准电容的性质.电极的理想电容性质在循环伏安图上表现为矩形[4],电极的容量是循环伏安曲线所包围的面积,由于电极的循环伏安图并不是规整的矩形,所以不能直接用矩形计算面积的公式求电极容量,而只能做定性与比较的分析.相比较而言,a电极在1mol/L的KO H溶液中的图形更接近矩形,阴极过程和阳极过程对称,表明电极具有良好的电容性能.b电极的电流虽然较大,是因为在制作b电极时,泡沫镍上附着的活性物质比a,c电极稍多所致.2.2.2　交流阻抗测试用三电极系统对上面制得的A ,B ,C 三试样进行交流阻抗测试.测试结果表明a 电极的内阻明显小于b ,c 电极的内阻.a ,b ,c 三电极分别在1mol /L KOH 溶液中,正弦波幅值为5mV ,频率范围是10m Hz ～2kH z ,得到交流阻抗曲线.图4是a ,b ,c 三电极的交流阻抗曲线.从图中可以看到:a ,b ,c 三电极的阻抗特性曲线都存在圆弧部分,表现了法拉第准电容和法拉第阻抗的存在.2.2.3　恒电流充放电测试a ,b ,c 分别在1m ol /L KOH 水溶液中进行充放电测试,充放电的电流是10mA.实验结果表明,a 电极在1mol /L KOH 溶液中比容量明显优于b ,c 电极的比容量.图5是a ,b ,c 电极分别在1m ol /L 的KOH 溶液充放电曲线.图5显示,a ,b ,c 三电极的充放电曲线呈现出典型的三角形对称分布,均表现出理想的电化学电容特性.但是由于制作a ,b ,c 三电极所用的M nO 2内部结构以及外在的形貌的不同,他们的质量比容量是不相同的.电极材料的单电极质量比容量(C p )计算公式可用下式表示:C p =d Q d V =i d t /d V w =i (d V /d t )w 式中Q 表示电极上存储的电荷(c );V 表示电极电位(V );i 表示循环伏安的电流(A );d V /d t 表示扫速;w 是活性物质的质量(g ).由于制作电极时所用的电极材料的质量是相等,又在相同的电流下进行充放电测试,因此活性物质的比电容(C p )大小与扫速成反比.从图5可以直观的看到a 电极的比容量明显优于b ,c 电极的79第1期常照荣等:湿法制备纳米二氧化锰及其电化学性能的研究比容量.a ,b ,c 三电极的充放电曲线都产生了一定的变形,这可能是有限的接触面积使活性物质的氧化还原反应滞后于电流的变化造成的.2.2.4　在锂电池中的插锂行为用两电极系统对制备的A ,B ,C 三种试样进行放电实验.结果表明,a 电极在1m LiPF 6+PC /DM E 中的放电比容量高于b ,c 电极的放电比容量.图6分别是a ,b ,c 三电极从开路电压到1.5V 的放电曲线.从图中看到,a 电极不仅有较高的放电比容量,而且还有较高的开路电压和放电平台,表明氧化法制得的无定形MnO 2更有利于锂离子的插入.据有关文献报道,M nO 2粉体结构中含有微量的钠离子[3],其具有较大的比容量.由于A 试样是用钠盐制备,而B 、C 试样是用钾盐制备,这也可能是氧化法具有较好插锂性能的原因之一.在C /10的放电倍率下,a ,b ,c 三电极的放电比容量分别为180.14,58.48,103.78mAh /g.3　结　论3.1　用湿法制备纳米MnO 2,得到是无定型产物,并且产物的颜色由反应液的酸碱性决定:酸性反应液得到黑色M nO 2粉体,碱性反应液得到棕色M nO 2粉体.3.2　用湿法制备三种纳米M nO 2,在KOH 电解液中,均具有法拉第准电容性能,其中氧化法制备的M nO 2电容性能最好.3.3　用氧化法制备的纳米M nO 2在锂离子电池中表现出良好的插锂行为.参　考　文　献[1]　Bach S ,Pe reir a -Ramos J P ,Baffier N.A new M nO 2tunnel related phrase ad host lattice for Li intercalation [J ].Solid State Io nics ,1995,80(2):151-158.80河南师范大学学报(自然科学版) 2006年[2]　Xu J J ,Y ang J.N ano structured amor phous mang anese o xide cryo gel ad a hig h -rate lithium intercalatio n host [J ].Elect ro -chemistry communicatio ns ,2003,5(3):230-235.[3]　常照荣,吴　锋,徐秋红,等.锂离子蓄电池正极材料制备方法的新进展[J ].河南师范大学学报(自然科学版),2005,33(1):63-68.[4]　H ong M S ,L ee S H ,K im S W.U se of K Cl aqueo us electr oly e fo r 2V mang anese ox ide /activ ated carbon hy brid capacitor[J ].Elect rochemical and So lid -State L etter ,2002,5(10):A227-A 230.[5]　闪　星,张密林,董国君,等.纳米二氧化锰的制备及在超大容量的电容器中的应用[J ].电源技术,2002,26(2):92-94.Studies on Preparation and Electrochemical Performancefor Nano -Mn O 2with Wet Chemical MethodCH ANG Zhao -rong ,LIU Yuan -y ing ,TANG Ho ng -w ei ,LI Yun -ping(College of Chemis try and E nvironmental Science ,Henan No rm al University ,Xin xiang 453007,China )A bstract :T hree kinds of mang ane se dioxide we re prepared by ox idatio n ,r eduction a nd r edo x metho d in aqueo us solu -tion ,r espectively.X -ray diffraction (X RD ),scanning electr on micro sco py (SEM ),cyclic vo ltammetry (CV ),alter na ting cur -rent impedance and constant current cha rge -discha rge tests w ere used to char acte rize the structure ,mo rpho log y and elect ro -chemical perfo rmance of the samples.T he results show ed that the M nO 2po wder sy nthe sized w as amo rpho us ,agg lomera te na n -o meter spherical par ticles ,and M nO 2by prepara tion with o xidatio n method exhibited better capacito r pe rfor mance and hig her discharg e capacity.Key words :supe rcapacitor ;Lithium ba tteries ;M nO 2electro de ;electro de material (上接第76页)[15]　Lee M C ,Snoeyink V L ,Crittenden J C.Activated ca rbo n adsor ption of humic substances [J ].A WW A ,1981,73(8):440-447.[16]　曾抗美,李乃稳,肖　芳,等.活性碳多维电极法去除水中腐殖酸过程与宏观动力学研究[J ].环境污染治理技术与设备,2003,4(3):31-34.[17]　A ndersen D O.Na ture of na tural or ganic ma te r (N O M )in acidified and limed surface w aters [J ].Wat Res ,2000,34(1):266-272.Research on Relationship between Humic Acid Concentrationsand ClO 2Dosage in Water SamplesGE Yuan -xin ,ZH U Zhi -liang ,ZH AO Jian -fu(S tate Key Lab oratory of Pollution C on trol and Resource Reu se ,T ongji University ,S hang hai 200092,China )A bstract :Fo r the reactio n sy stem be tween humic acid and eno ug h ClO 2in water samples ,the changes of residua l ClO 2,T OC ,U V 254,U V 410and CO D Mn under different co nditio ns we re inv estiga ted.T he results show ed that the maximum dema nd o f ClO 2is 2.19mg /mg T O C ,the change tendency o f residual ClO 2was similar to that in the situatio n of Cl 2as disinfectio n rea -g ent ,TO C and COD M n of humic acid decreased 15%and 19%respectiv ely ,21%o f UV 254and 49%o f U V 410w ere remov ed un -der the ex perimental conditions.It wa s also demonstrated that ClO 2had a n effective affect to reduce T HM s fo rmatio n potential of humic acid and co lo r of w ater samples.Key words :humic acid ;ClO 2;r emoval ra tio ;drinking wa te r 81第1期常照荣等:湿法制备纳米二氧化锰及其电化学性能的研究。

化工专业英语例句摘录(2)-电极材料

期刊文献中的英文句子摘录（3）原文：This small-sized molecule is incapable to be carbonized into 2D carbonnanosheets since it could escape from the gallery of HNTO during the processes of thermal polymerization and carbonization.翻译：由于这种小分子无法在热聚合和碳化过程中从HNTO通道中逸出，因此无法碳化成2D碳纳米片。

出处：DOI: 10.1021/acsami.0c03775原文：Metal sulfides as promising SIB anode material s have merits of hightheoretical capacities, better reversibility, and relatively higher electronic conductivity than metal oxides counterparts.翻译：金属硫化物作为有希望的SIB负极材料，具有比金属氧化物对应物更高的理论容量，更好的可逆性和相对更高的电子电导率的优点。

出处：10.1007/s40820-020-0367-9原文：Carbon materials have been investigated as electrode materials forelectrochemical energy storage and capture owing to their large surface area, electrical conductivity, electrochemical, thermal, and mechanical stabilities, diverse morphologies and chemistries.翻译：碳已经成为研究电化学能量捕获存储的电极材料，这是由于其表面积大，导电性，电化学，热和机械的稳定性以及不同的形态具有的化学性质。

AgNi合金作为直接硼氢化物燃料电池的阳极催化剂

[Note]物理化学学报(Wuli Huaxue Xuebao )Acta Phys.鄄Chim.Sin .,2007,23(6)：932-934JuneReceived:November 23,2006;Revised:January 15,2007;Published on Web:April 29,2007.∗Corresponding author.Email:ece@;Tel:+8627⁃68754526.国家自然科学基金(20573080)资助项目ⒸEditorial office of Acta Physico ⁃Chimica SinicaAgNi 合金作为直接硼氢化物燃料电池的阳极催化剂冯瑞香曹余良艾新平杨汉西∗(武汉大学化学与分子科学学院,武汉430072)摘要：采用机械球磨法制备银镍合金,并将其用作直接硼氢化物燃料电池(DBFC)的阳极催化剂.XRD 和SEM 实验表明,这种催化剂为纳米粒子集聚的微米颗粒,具有二元合金的典型结构特征.电化学实验表明,AgNi 合金不仅能够催化硼氢化物的直接电化学氧化,而且可以抑制硼氢化物的化学水解.当采用AgNi/C 作为DBFC 电池的阳极催化剂时,硼氢化钾的放电容量在3500mAh ·g -1以上,对硼氢化物燃料的利用率可达90%以上.关键词：银镍合金;机械球磨;硼氢化物;燃料电池中图分类号：O643;O646AgNi Alloy Used as Anodic Catalyst for Direct Borohydride Fuel CellsFENG Rui ⁃Xiang CAO Yu ⁃Liang AI Xin ⁃Ping YANG Han ⁃Xi ∗(College of Chemistry and Molecular Science,Wuhan University,Wuhan430072,P.R.China )Abstract ：AgNi alloy power was prepared as anodic catalyst for direct borohydride fuel cells by mechanical ball ⁃milling method.The XRD and SEM evidences revealed that the alloy powder was composed of nanosized crystallites aggregated into micrometer particles.It was found from electrochemical experiments that the AgNi catalyst could not only catalyze the direct electrochemical oxidation of borohydride ions,but also depress the chemical hydrolysis of borohydride ions,so as to produce a discharge capacity of KBH 4over 3500mAh ·g -1,which corresponded to a 90%utilization of the BH -4ions as anodic fuel.Key Words ：AgNi alloy;Mechanical ball ⁃milling;Borohydride;Fuel cells质子膜燃料电池(PEMFC)由于在能源技术方面具有广泛的应用前景,近年来受到特殊的重视[1,2].目前基于氢燃料的PEMFC 技术相当成熟[3],但氢的制备和储存仍是一项技术难题,而采用甲醇燃料的PEMFC [4]则更存在电催化等问题.我们发现,以硼氢化物为燃料构建直接硼氢化物燃料电池(DBFC)[5-9],可能具有比能量高、阳极反应动力学快、燃料易储存和运输等优点.尽管DBFC 体系具有上述潜在优点,然而这一体系的实际应用仍需解决两个问题:一是BH -4的内透(crossover),二是高效廉价的BH -4的阳极催化剂.前一问题可以通过选择对BH -4无催化作用的阴极催化剂加以解决[9];而后一问题的解决则需要发展一种合适的催化剂,既可催化BH -4的直接电化学氧化反应,同时又不会催化其化学水解产氢.虽然许多金属,比如金[7]、铂[10]、镍[11]等,可以催化BH -4的电化学氧化反应,但这些金属各有缺点.金和铂的价格昂贵,且阳极电催化活性并不令人满意[9,10].镍对BH -4电化学氧化反应催化活性较高,同时对其化学水解的催化活性也很高,致使BH -4的阳极利用率最高仅为50%[11].为解决这一问题,我们采用合金化的方法制备了系列双功能催化剂,试图发展一种既可催化BH -4直接电化学氧化,同时又不催化其化学水解的高效阳极催化剂.本文报道AgNi/C 复合催化剂对于BH -4阳极反932No.6冯瑞香等：AgNi 合金作为直接硼氢化物燃料电池的阳极催化剂应的电催化行为.1实验1.1材料制备AgNi/C 的制备方法是将银粉(99.5%,上海)与镍粉(99.8%,上海)按质量比40∶60混合,置于高速摆震球磨机中(QM ⁃3A,南京)球磨20h,得到银镍合金粉.将银镍合金粉置于管式炉中在氩气气氛下400℃灼烧2h 后,再与XC ⁃72炭粉按质量比1∶1混合并在氩气气氛下球磨1h,得到AgNi/C 复合物.将AgNi/C 粉与聚四氟乙烯乳液按质量比90∶10混合碾压成膜,并在2.5×106Pa ·cm -2的压强下将其压在钢网上作为硼氢化物直接燃料电池阳极催化电极.1.2结构表征与电化学测试AgNi 合金的晶体结构和颗粒形貌分别采用X 射线粉末衍射仪(Shimadzn Lab XRD ⁃6000,日本)和扫描电镜(Sirion 2000,FEI,荷兰)测定.循环伏安实验采用三电极电解池进行测试.按研究需要,分别采用AgNi 合金、Ag 和Ni 粉制备的膜电极为工作电极.对电极为较大面积的的镍片,参比电极为HgO/Hg 电极.所用仪器为CHI600型电化学工作站(辰华,上海).放电性能采用模拟电池在新威电池测试系统(BTS ⁃0550,深圳)上进行恒电流放电测试,以AgNi/C 作为催化阳极,含二氧化锰催化剂的空气电极作为阴极,0.1g KBH 4/10mL 2mol ·L -1KOH 为电解液.2结果与讨论2.1AgNi 合金的结构与形貌图1为AgNi 合金、Ag 和Ni 的X 射线衍射图.从图中可以看出,银与镍混合球磨20h 后的粉末样品包含金属Ag 、Ni 所有的特征峰.与AgNi 合金的相图对比可知[12],此时的样品已不再是银和镍粉的简单混合,两者已发生合金化.经球磨后各特征XRD 衍射峰明显变宽,表明合金化过程也使样品粒径变小.图2为AgNi 合金的扫描电镜图谱.从放大倍率为1000的图2a 上看到,AgNi 合金的平均粒径范围为5-10滋m.而放大50000倍后的图2b 显示,AgNi 合金颗粒的表面覆盖着大量纳米级的小颗粒.根据XRD 衍射峰数据,这些纳米小颗粒的粒径可由Scherrer 公式计算:d =0.9λ/(B cos θ)代入X 射线波长λ=0.154056nm,AgNi(220)晶面衍射峰的半高宽为3.0764,该晶面衍射角θ=32.007°,计算出的纳米颗粒的平均粒径为3.1nm.2.2AgNi 合金对KBH 4的催化行为图3为KOH 溶液中Ag 、Ni 和AgNi 合金的阴极扫描曲线.从图中可看出,在Ag 电极上直到-1.3V 才出现析氢电流,即表现出很大的析氢超电势.在Ni 电极上在-0.5V 处即可观察到水的还原电流,说明此时已开始发生氢的吸附反应,即镍表现出很低的氢超电势.与前两者相比,AgNi 合金上的水还原电位处于两者之间,表现出低于银而高于镍的氢超电势.这样,采用AgNi 合金催化剂可保持镍对KBH4图3KOH 溶液中Ag,Ni 和AgNi 合金的阴极CV 曲线Fig.3The CV curves of Ag,Ni and AgNi alloyin KOHsolution图1AgNi 合金,Ag 和Ni 粉的XRD 特性图Fig.1XRD patterns of AgNi alloy,Ag and Ni powders图2AgNi 合金粉的SEM 图Fig.2SEM images of AgNi alloypowder933Acta Phys.鄄Chim.Sin.,2007Vol.23的电氧化活性,同时抑制KBH 4的化学水解反应.图4给出了KBH 4在AgNi 合金上的阳极氧化伏安曲线.在KOH 溶液中,AgNi 合金上的阳极氧化电流起峰于+0.15V 左右(图4b),与银的电化学氧化电势相吻合.当溶液中含有KBH 4时,在约-0.4V 处出现一很强的氧化电流峰.由于在此电势区不可能出现水的氧化反应,该氧化电流可归因于BH -4的电化学氧化.对照镍和银在KBH 4溶液中的循环伏安曲线[13,14],AgNi 合金的循环伏安特性完全不同于前两者,表现为两种元素的协同作用.2.3KBH 4的放电特性图5给出了AgNi/C 为阳极催化剂时直接硼氢化物燃料电池的放电曲线.KBH 4⁃O 2燃料电池的理论电压为1.64V,而实际开路电位约为0.7V,其原因为阴极和阳极反应的动力学速率均较慢[15].当以较小电流密度(1mA ·cm -2)放电时,电池放电平台可保持在0.45V 左右,放电容量达到3672mAh ·g -1,相当于每个KBH 4分子的反应电子数为7.4个.对于BH -4而言,完全电化学氧化时理论上可放出8个电子,而在AgNi/C 催化电极上能够放出7.4个电子,说明AgNi/C 催化电极可使BH -4的利用率达到了92%以上.当电流密增大至4mA ·cm -2时,电池电压迅速降至0.2V,表明阳极的电化学极化仍十分严重.然而,即使电流密度为4mA ·cm -2时,BH -4的放电容量仍达3578mAh ·g -1,即可放出90%以上的理论容量.3结论通过机械球磨法制备的AgNi 合金,既保持了镍对于BH -4电氧化的催化活性,又体现出银对BH -4化学水解的惰性.AgNi 合金作为直接硼氢化物燃料电池的阳极催化剂,可使硼氢化钾的放电容量在3500mAh ·g -1以上,释放出90%以上的理论容量.References1Waintight,J.S.;Savinell,R.F.;Liu,C.C.;Litt,M.Electrochim.Acta,2003,48:28692Pozio,A.;Silva,R.;Francesco,M.;Cardellini,F.;Giorgi,L.Electrochim.Acta,2003,48:16273Chen,Y.;Xu,H.;Wang,Y.;Jin,X.;Xiong,G.Fuel Processing Technology,2006,87:9714Lasch,K.;Hayn,G.;Jorissen,L.;Garche,J.;Besenhardt,O.J.Power Sources,2002,105:3055Liu,B.H.;Li,Z.P.;Arai,K.;Suda,S.Electrochim.Acta,2005,50:37196de Leon,C.P.;Walsh,F.C.;Pletcher,D.;Browning,D.J.;Lakeman,J.B.J.Power Sources,2006,155:1727Amendola,S.C.;Onnerud,P.;Kelly,M.T.;Petillo P.J.;Sharp ⁃Goldman,S.L.;Binder,M.J.Power Sources,1999,84:1308Li,Z.P.;Liu,B.H.;Arai,K.;Suda,S.J.Electrochem.Soc.,2003,150:A8689Feng,R.X.;Dong,H.;Wang,Y.D.;Ai,X.P.;Cao,Y.L.;Yang,mun.,2005,7:44910Elder,J.P.Electrochim.Acta,1962,7:41711Liu,B.H.;Li,Z.P.;Suda,S.J .Electrochem.Soc.,2003,150:A39812http://www.crct.polymtl.ca/FACT/documentation13Dong,H.;Feng,R.;Ai,X.;Cao,Y.;Yang,H.;Cha,C.J.Phys.Chem.B,2005,109:1089614Chatenet,M.;Micoud,F.;Roche,I.;Chainet,E.Electrochim.Acta,2006,51:545915Wang,Y.;Xia,mun.,2006,8:1775图4AgNi 合金在2mol ·L -1KOH 溶液中(a)含0.01mol ·L -1KBH 4或(b)空白溶液的阳极CV 曲线Fig.4CV curves of the AgNi alloy electrode in 2mol ·L -1KOH solution (a)with or (b)withoutaddition of 0.01mol ·L -1KBH4图5AgNi/C 作为阳极催化剂时DBFC 电池的放电曲线Fig.5The discharge curves of the DBFC with AgNi/Cas anodic catalyst934。

High capacity graphite-silicon composite anode material for lithium-ion batteries

Electrochimica Acta52(2006)973–978Nano silicon for lithium-ion batteriesMichael Holzapfel a,∗,Hilmi Buqa a,1,Laurence J.Hardwick a,Matthias Hahn a,Andreas W¨u rsig a,2,Werner Scheifele a,Petr Nov´a k a,R¨u diger K¨o tz a,Claudia Veit b,Frank-Martin Petrat ba Paul Scherrer Institut,Electrochemistry Laboratory,CH-5232Villigen PSI,Switzerlandb Degussa AG,Paul-Baumann-Str.1,Building1420/18,D-45764Marl,GermanyReceived6February2006;received in revised form3May2006;accepted28June2006Available online8August2006AbstractNew results for two types of nano-size silicon,prepared via thermal vapour deposition either with or without a graphite substrate are presented. Their superior reversible charge capacity and cycle life as negative electrode material for lithium-ion batteries have already been shown in previous work.Here the lithiation reaction of the materials is investigated more closely via different electrochemical in situ techniques:Raman spectroscopy, dilatometry and differential electrochemical mass spectrometry(DEMS).The Si/graphite compound material shows relatively high kinetics upon discharge.The moderate relative volume change and low gas evolution of the nano silicon based electrode,both being important points for a possible future use in real batteries,are discussed with respect to a standard graphite electrode.©2006Elsevier Ltd.All rights reserved.Keywords:Nano silicon;Graphite;Lithium-ion batteries;Composite electrodes;Rechargeable1.IntroductionLithium-ion batteries are now the cell-of-choice to power portable electronic applications;more than a billion cells were sold in2004.Due to their high energy density(more than twice the one of NiMH batteries)and very high efﬁciency(up to95% overall),there is more and more discussion for the utilisation of lithium-ion batteries in electric vehicles(EVs)and hybrid-electric vehicles(HEVs).For the negative electrode,in general,graphitic carbon is used because it shows relative safety upon cycling when compared to lithium metal.Due to graphite’s relatively low electrochemi-cal charge capacity(theoretical value:372mAh g−1),however, the search for alternative negative electrode materials has been intensiﬁed,above all in theﬁeld of lithium–metal alloys.Well-known examples are aluminium[1],tin[2,3],antimony[3],etc.∗Corresponding author.Tel.:+41563102116;fax:+41563104415.E-mail address:michael.holzapfel@psi.ch(M.Holzapfel).1Present address:High power Lithium S.A.,PSE B,EPFL,CH-1015Lau-sanne,Switzerland.2Present address:Fraunhofer Institute for Silicon Technology(ISIT),Fraun-hoferstr.1,D-25524Itzehoe,Germany.for binary alloys or copper–tin[4],copper–antimony[5],etc.for ternary alloys.In these systems,the metal reversibly forms alloys with lithium,which have very high capacities.A general disad-vantage of alloy electrodes,however,is the huge volume change which occurs upon the insertion/deinsertion of the lithium.It can attain values of more than200–300%[6]and leads to mechanical fatigue upon prolonged cycling.Much research has been conducted on silicon,as it reversibly forms,alike tin,electrochemically active binary alloys with lithium[7–9].They can show a very high lithium insertion capacity of approx.4200mAh g−1(for a theoretical composi-tion of Li4.2Si).This very high lithium content is accompanied by a huge volume change(of more than300%),which leads to strong mechanical stress on the crystallites and,thus,to break-ing and amorphisation of the particles and loss of the electrical contact[10–12].A rapid loss of the reversible capacity upon prolonged cycling(fading)generally results.Besides the deposition of the silicon as a sub-micrometer thinﬁlm on a strongly adhering support by chemical vapour deposition[12–16]there are several other ways that have been explored.Intensive ball-milling to decrease the particle size and enhance the electric contact[17,18],carbon coating starting from the gas phase[19],and pyrolysis of an intimate mixture0013-4686/$–see front matter©2006Elsevier Ltd.All rights reserved. doi:10.1016/j.electacta.2006.06.034974M.Holzapfel et al./Electrochimica Acta52(2006)973–978of precursors[20]have been adopted.Indeed,a reduction of the irreversible losses and,hence,an increase in the reversible charge capacity and cycle life could have been obtained,but in any case the cycle life was below100cycles.Other techniques for an eventual stabilisation of silicon negative electrodes could be the use of an additive which counterbalances irreversible losses during theﬁrst cycles(e.g.Li2.6CoN,cf.[21]),or the use of an inert,buffering,metal matrix for the electrochemically active silicon[22,23].A reduction of the particle size into the nanometre range can reduce the mechanical stress.An early study[19],showed the favourable behaviour of nano silicon/carbon composites.Recent literature[15,24,25]shows that with nano-scale materials capac-ities up to1700mAh g−1,together with reduced fading can be reached.However,such materials are not yet comparable to com-mon graphite electrodes as they suffer from low cycle life and high fading.Wang et al.[26]recently presented composite elec-trodes based on nano silicon inclusions in carbon aerogel.These electrodes show a stable charge capacity of1450mAh g−1.The same group prepared also a promising high-capacity composite electrode by ball-milling,but these electrodes still suffer from a relatively high fading[27].In this study we present nano-scale silicon materials,prepared by thermal vapour deposition,showing excellent electrochemi-cal properties,above all high reversible speciﬁc charge capacity and low capacity fading during cycling.The relative volume changes of the composite electrode upon lithium uptake and release are shown not to be higher and the gas evolution to being less than for standard graphite.Two types of materials are presented:theﬁrst one is a com-posite electrode based on an intimate mixture of the nano silicon with a small particle graphite(TIMREX KS6;20and80wt.% Si).For the80wt.%silicon electrode also2%of TIMREX Super P carbon black have been added.The second material is based on direct deposition of the nano silicon on the surface of theﬁne particle graphite.In the following,this material is called“com-pound material”.Preliminary results concerning both materials have already been communicated[28,29].Both materials show impressive results with respect to their high reversible charge capacity,low irreversible capacity upon prolonged cycling and both,long cycle life and low capacity fading.Theﬁrst cycles are particularly characterised by in situ Raman microscopy,slow scan cyclic voltammetry,dilatometry measurements and mea-surements on gas evolution upon cycling.2.ExperimentalThe nano silicon material was produced by a pyrolysis pro-cess of mono silane(SiH4),either without substrate to form the nano silicon,or with TIMREX KS6(TIMCAL SA,Bodio, Switzerland)ﬁne particle graphite as substrate,to form the “compound”material.The composite electrodes were prepared as follows:the sili-con material(20wt.%)is mixed with70wt.%of TIMREX®KS6 and10%of SOLEF®PVdF1015binder(Solvay SA,Belgium) in a N-methylpyrrolidone solution,mixed thoroughly and cast on a pre-treated(with a polymer based primer from Contitech,Nordhausen,Germany)copper foil which serves as current col-lector.The primer enhances the adherence of the active material on the copper.The typical mass load is of2–3mg/cm2.The “compound”electrode is made in the same manner by mix-ing the active material with10%SOLEF®PVdF1015binder. Lithium metal is used as counter electrode in both cases.The electrolyte used is battery grade ethylene carbonate and dimethyl carbonate(1:1),with1M LiPF6to which2%of vinylene car-bonate were added and was obtained from Ferro Corp.(USA). The electrochemical measurements were conducted in com-bined galvanostatic-potentiostatic protocol.First,classical gal-vanostatic(constant current)cycling with a speciﬁc current of 74mA g−1(10mA g−1in theﬁrst cycle)was performed until a lower voltage limit of5mV versus Li/Li+and an upper volt-age limit of1.0V versus Li/Li+,respectively,for the charge and discharge.At the end of each charge and discharge step a poten-tiostatic step followed with a reduction of the current,at theﬁxed upper or lower potential limit,respectively,down to a value of 5mA g−1,to complete the charge/discharge(the charge capacity which passes at this potentiostatic step generally represents less than5%of the total speciﬁc charge capacity).The cells were cycled galvanostatically by means of a computer-controlled cell capture system CCCC(Astrol Electronics AG,Oberrohrdorf, Switzerland).A confocal Raman microscope(Labram series,Jobin Yvon SA,ex DILOR SA),using a He–Ne laser at632.8nm with ca. 1mW power as the excitation source,was used to acquire the in situ Raman spectra.Raman band positions were calibrated against the spectrum of a neon lamp(Penray,Oriel)with a reso-lution of4cm−1with an80×objective.Each spectrum required 180s measurement-time,and because of the acceptable signal to noise ratio,with only one accumulation with a confocal res-olution of2–3␮m3.For the thickness variation measurements we used a purpose made dilatometer[30].This consists of a cell stack,the active electrode and a LiCoO2counter electrode separated by aﬁxed glass diaphragm.This assembly is soaked with electrolyte.A lithium wire serves as reference.The working electrode is free to move against a constant load(20N)applied by means of a spring.The lower(and much bigger)electrode isﬁxed and serves as the counter electrode.The overall height change of the cell is monitored by an inductive displacement transducer mounted on top of the plunger which contacts the working electrode.As the glass diaphragm cannot move,the measured expansion can be solely attributed to the working electrode.The gas evolution experiments have been performed in an all titanium electrochemical cell with in situ head space gas analysis underﬂowing argon using a quadrupole mass spectrometer(cf.[31]).3.Results and discussionThe composite electrode is a homogeneous dispersion of the silicon particles within the graphite matrix.The silicon parti-cles form long aggregates,with diameters of some100–200nm, intimately connected to the larger graphite particles.For the “compound”material the silicon forms small(20nm)spher-M.Holzapfel et al./Electrochimica Acta 52(2006)973–978975ically shaped particles on the surface of the graphite.Both materials have been described in more detail in previous com-munications [28,29].The materials show impressive speciﬁc charge (up to 1000mAh g −1for the composite material)and cycling stability upon electrochemical cycling [28,29].The good behaviour of both types of electrodes has been attributed to several important points.First,a much smaller mechanical degradation upon the intercalation/deintercalation process which is probably due to the very small particle size and the favourable distribution within and good electrical contact to the supporting graphite/carbon black matrix (cf.also Liu et al.[32]).Second,to a favourable electrode manufacture,i.e.the larger amount of graphite accom-modating the volume change of the silicon.Third,in the case of the compound electrode,the fact that the silicon parti-cles are chemically bound on the graphite surface.This pre-vents contact loss during the huge volume change upon the lithiation–delithiation process via the vapour deposition process.In addition one has to note that the homogeneous distribution of the nano silicon particles on the graphite reduces the inﬂuence upon the neighbouring Si particles and hence the mechanical stress upon cycling.Fig.1shows slow scan cyclic voltammograms of the ﬁrst lithiation/delithiation of the 20%composite and the “com-pound”electrode compared to a KS6graphite electrode,respectively,below 0.6V versus Li/Li +,where the reversible lithium insertion takes place.For the graphite electrode,the lithium intercalation/deintercalation potentials are practically unchanged for the ﬁrst and the second cycle.However,the sili-con containing electrodes behave differently.Both show apeakFig.1.Slow scan cyclic voltammetry (5␮V/s)on both silicon-based electrodes,compared to graphite.The speciﬁc current is given in mA g −1of active material.shift to lower potentials upon ﬁrst lithiation,in relation to both,their second cycles and to graphite.This overpotential can be attributed on the one hand to the semiconducting behaviour of silicon which is a poor electronic conductor in its pristine state and should become conductive after partial ﬁlling of the con-duction band with electrons during lithium insertion.On the other hand it can be attributed in part also to the breaking of the crystal structure upon the ﬁrst lithiation.The kinetics of the electrochemical reaction are thus greatly enhanced (and the over-potentials for charge transfer are reduced)once the Si particles have been lithiated.This causes that the ﬁrst and second delithi-ation do not show major differences but that the potentials of the peaks in the second lithiation are shifted to the right,compared to the ﬁrst cycles,for the silicon containing materials.The typical features of graphite can be acknowledged in all three materials.The signatures coming from the silicon are mostly visible,for the lithiation reaction,as unspeciﬁed features at voltages above 200mV versus Li/Li +and increasing the intensity of the graphite signal.Upon delithiation,both an increasing of the intensity of the graphite pattern and a distinct peak between 400and 500mV versus Li/Li +,reminiscent of the delithiation of crystalline lithi-ated silicon phases formed [9],can be acknowledged.The ﬁrst lithiation reaction was followed using in situ Raman microscopy (Fig.2)at several points on the surface,two of which are shown.Both points (A)and (B)(with different inten-sity)display a prominent silicon signal with the most notable Raman feature seen at ca.518cm −1,with a full width at half maximum (FWHM)of 6cm −1.This can be assigned to the scat-tering of the ﬁrst order optical phonon mode (TO).Two peaks at ca.300and 950cm −1can also be observed and these are assigned to the scattering of the second-order transverse acous-tic phonon mode (2TA)and the second-order optical phonon mode (2TO),respectively [33–35].The main bands ofgraphiteFig.2.In situ Raman spectroscopy of the lithium intercalation into a 20%nano silicon composite electrode.976M.Holzapfel et al./Electrochimica Acta 52(2006)973–978are also observed,with the D band seen at 1330cm −1,the G band at 1585cm −1([36]).During the ﬁrst lithium insertion into this material from the open circuit potential (ca.3V versus Li/Li +)to 170mV versus Li/Li +the silicon lines are seen to rapidly dimin-ish and then disappear completely at most of the points of the surface (represented by point A).This is because of the inserted lithium breaking down the sp 3symmetry of the structure.The diamond-like structure of silicon becomes amorphous through lithium insertion.This observation is in agreement with previous Raman measurements upon nano silicon,where a decrease of the 520cm −1band was also detected [37].The decrease in intensity of the TO mode of silicon,for all points,can be observed.The intercalation spectral characteristics of graphite are also seen,especially at 170mV versus Li/Li +where the stages 3and 4GIC G-Band doublet appears [38–40](represented by point B).The return to a single band seen at 1590cm −1below 155mV indicates a stage 2GIC and is detected at lower potentials (not shown).Some additional points measured still displayed a typical open circuit potential spectrum for the silicon.These measurement points could have been isolated particles.For the ﬁrst delithiation no reappearance of a silicon line,at 520cm −1,was detected for any of the points measured during the cycling of potential from 5mV to 1.5V versus Li/Li +.With the early decrease of the silicon line during the ﬁrst lithium insertion it is unlikely a sufﬁcient amount of lithium leaves the silicon for the initial crystalline structure to return for the TO mode of silicon to be detectable.The reappearance of graphite doublet G-band returning to singlet G band (ca.1580cm −1)is observed.This indicates that lithium is deintercalating from the graphite present in the electrode (not shown).Fig.3shows the electrochemical cycling behaviour of the “compound”material at different speciﬁc current rates.The charge reaction has always been done at C /7.4rate in order to have comparable conditions for each cycle (50mA g −1;the C -rate is given here with respect to the theoretical speciﬁc capac-ity of graphite,i.e.372mAh g −1).The galvanostatic discharge rate was varied between rates of C /7.4and 10C (50mA g −1to 3.72A g −1).This high current regime was followed by apoten-Fig.3.Rate capability behaviour of the nano silicon “compound”electrode.The C rate is given with respect to graphite,i.e.C /1corresponds to 372mA g −1.tiostatic regime down to a speciﬁc current of 10mA g −1,in order to compare the galvanostatic (high regime)capacity to the total electrochemical discharge capacity.It can be seen that,even if the fading is somewhat higher than for normal cycling,the total capacity is not affected much by high rates.The galvano-static discharge capacity of the “compound”material decreases steadily with the discharge rate,but the value always remains higher than the total capacity of graphite and reaches this value only for 10C (3.72A g −1).The high rate capability of different types of graphite already shown in a recent study [41]is hence affected only little for the silicon coated “compound”material.As discussed in the introduction,the main problem of sil-icon and comparable materials (tin,antimony,aluminium)is the important volume change upon the electrochemical reaction with lithium.However,as mentioned above,if the material is present as sufﬁciently small particles,the mechanical stress is reduced.Secondly,if the electrical contact is well maintained by intimate mixing in an adapted conductive matrix,the loss of contact leading to capacity fading can be minimised.Besides the problem of the volume change of the particles themselves,also the volume change of the entire electrode is an important question in a real lithium-ion battery.Fig.4shows the evolu-tion of the relative change of the electrode thickness of a 20%nano silicon composite electrode.The speciﬁc charge capacities are (in mAh g −1)for this experiment:ﬁrst charge 940,ﬁrst dis-charge 780,second charge 750,second discharge 720.The lower capacity,when compared to the results presented in Ref.[28],comes from the fact that the dilatometry cell used is not optimally designed for proper electrochemistry.A practically linear thick-ness change can be observed along with galvanostatic cycling,i.e.that a given amount of lithium inserted or deinserted accounts for the same volume change,irrespective of whether silicon or graphite is the host material.Only at the beginning of the delithi-ation reaction a lower slope can be acknowledged,which could be related to the stages I–II transformation of the graphite.A comparison to dilatometry measurements performed on graphite [42]reveals that,indeed,the relative thickness change per spe-ciﬁc capacity is comparable for graphite andsilicon/graphiteFig.4.Thickness variation of a 20%nano silicon composite electrode during electrochemical cycling.M.Holzapfel et al./Electrochimica Acta52(2006)973–978977Fig.5.Gas evolution for a nano silicon graphite electrode compared to a graphite electrode upon theﬁrst electrochemical cycle.electrodes.This means that the use of a material with inherent high volume change does not necessarily lead to a higher volume change in an electrode made out of it.The use of silicon-based material,with increased speciﬁc capacity,in classic lithium-ion batteries would therefore not need a new battery design.Fig.5shows the comparative evolution of hydrogen and ethylene for both nano silicon and the graphite electrodes in the standard electrolyte ethylene carbonate:dimethyl carbonate (1:1),1M LiPF6+2%vinylene carbonate(VC),for approx-imately the same total charge capacity of the electrode.The amounts of active material were ca.40mg of graphite and ca. 15mg of the nano silicon/graphite composite,which accounts for approximately the same amount of electrochemically stored lithium.It can be seen that the gas evolution is4–5times less for the composite electrode which means that the nano silicon does not account for the reduction of the electrolyte under gas evolution.The pressure build-up within a lithium-ion battery could thus be reduced,which increases the safety of the battery.A comparable result has already been described by Wagner et al.for tin-based electrodes[43].4.ConclusionsThermal vapour deposition from silicon-containing precur-sors has lead to free nano-scale silicon and nano-scale silicon particles deposited on aﬁne particle graphite(the“compound”material).Upon theﬁrst lithiation the rapid formation of lithi-ated phases causes the early disappearance of the Raman signal and increases the kinetics for the lithiation reaction.The“com-pound”material shows a relatively high rate capability for the discharge reaction.The overall relative volume change of a nano silicon based electrode has been shown to be about the same as for classical graphite electrodes.Finally,the gas evolution is reduced when compared to graphite electrodes. AcknowledgementThe authors express their gratitude to Dr.Frank Krumeich (ETH Z¨u rich,Switzerland)for his valuable help and fruitful discussions.References[1]M.J.Lindsay,G.X.Wang,H.K.Liu,J.Power Sources119(2003)84.[2]M.Winter,J.O.Besenhard,Electrochim.Acta45(1999)31.[3]J.L.Tirado,Mater.Sci.Eng.R-Rep.40(2003)103.[4]K.D.Kepler,J.T.Vaughey,M.M.Thackeray,Electrochem.Solid-State Lett.2(1999)307.[5]J.Yang,M.Wachtler,M.Winter,J.O.Besenhard,Electrochem.Solid-StateLett.2(1999)161.[6]J.O.Besenhard,J.Yang,M.Winter,J.Power Sources68(1997)87.[7]W.J.Weydanz,M.Wohlfahrt-Mehrens,R.A.Huggins,J.Power Sources82(1999)237.[8]R.N.Seefurth,R.A.Sharma,J.Electrochem.Soc.124(1977)1207.[9]T.D.Hatchard,J.R.Dahn,J.Electrochem.Soc.151(2004)A838.[10]M.Winter,J.O.Besenhard,M.E.Spahr,P.Nov´a k,Adv.Mater.10(1998)725.[11]J.Yang,M.Winter,J.O.Besenhard,Solid State Ionics90(1996)281.[12]S.Bourderau,T.Brousse,D.M.Schleich,J.Power Sources82(1999)233.[13]S.Ohara,J.Suzuki,K.Sekine,T.Takamura,J.Power Sources119(2003)591.[14]H.J.Jung,M.Park,S.H.Han,H.Lim,S.K.Joo,Solid State Commun.125(2003)387.[15]H.J.Jung,M.Park,Y.G.Yoon,G.B.Kim,S.K.Joo,J.Power Sources115(2003)346.[16]J.Graetz,C.C.Ahn,R.Yazami,B.Fultz,Electrochem.Solid-State Lett.6(2003)A194.[17]N.Dimov,S.Kugino,M.Yoshio,Electrochim.Acta48(2003)1579.[18]J.J.Niu,J.Y.Lee,Electrochem.Solid-State Lett.5(2002)A107.[19]A.M.Wilson,J.R.Dahn,J.Electrochem.Soc.142(1995)326.[20]rcher,C.Mudalige,A.E.George,V.Porter,M.Gharghouri,J.R.Dahn,Solid State Ionics122(1999)71.[21]Y.Liu,K.Hanai,K.Horikawa,N.Imanishi,A.Hirano,Y.Takeda,Mater.Chem.Phys.89(2005)80.[22]M.D.Fleischauer,J.M.Topple,J.R.Dahn,Electrochem.Solid-State Lett.8(2005)A137.[23]H.Y.Lee,Y.L.Kim,M.K.Hong,S.M.Lee,J.Power Sources141(2005)159.[24]H.Li,X.J.Huang,L.Q.Chen,Z.G.Wu,Y.Liang,Electrochem.Solid-StateLett.2(1999)547.[25]B.Gao,S.Sinha,L.Fleming,O.Zhou,Adv.Mater.13(2001)816.[26]G.X.Wang,J.H.Ahn,J.Yao,S.Bewlay,H.K.Liu,mun.6(2004)689.[27]G.X.Wang,J.Yao,H.K.Liu,Electrochem.Solid-State Lett.7(2004)A250.[28]M.Holzapfel,H.Buqa,W.Scheifele,P.Novak,F.-M.Petrat,-mun.(2005)1566.[29]M.Holzapfel,H.Buqa,F.Krumeich,F.-M.Petrat,C.Veit,Electrochem.Solid-State Lett.8(2005)A515.[30]M.Hahn,O.Barbieri,F.P.Campana,R.K¨o tz,R.Gallay,Appl.Phys.A82(2006)633.[31]P.Novak,D.Goers,L.Hardwick,M.Holzapfel,W.Scheifele,J.Ufheil,A.Wuersig,J.Power Sources146(2005)15.[32]W.R.Liu,Z.Z.Guo,W.S.Young,D.T.Shieh,H.C.Wu,M.H.Yang,N.L.Wu,J.Power Sources140(2005)139.978M.Holzapfel et al./Electrochimica Acta52(2006)973–978[33]H.Richter,Z.P.Wang,L.Ley,Solid State Commun.39(1981)625.[34]B.B.Li,D.P.Yu,S.L.Zhang,Phys.Rev.B59(1999)1645.[35]S.L.Zhang,X.Wang,K.J.Ho,J.J.Li,P.Diao,S.M.Cai,J.Appl.Phys.76(1994)3016.[36]J.L.K.F.Tuinstra,J.Chem.Phys.53(1970)1126.[37]H.Li,X.J.Huang,L.Q.Chen,G.W.Zhou,Z.Zhang,D.P.Yu,Y.J.Mo,N.Pei,Solid State Ionics135(2000)181.[38]M.Inaba,H.Yoshida,Z.Ogumi,T.Abe,Y.Mizutani,M.Asano,J.Elec-trochem.Soc.142(1995)20.[39]W.W.Huang,P.Frech,J.Electrochem.Soc.145(1998)765.[40]L.Hardwick,H.Buqa,P.Novak,submitted for publication.[41]H.Buqa,D.Goers,M.Holzapfel,M.E.Spahr,P.Novak,J.Electrochem.Soc.152(2005)A474.[42]M.Hahn,O.Barbieri,F.P.Campana,R.Gallay,R.K¨o tz,Proceedings of the14th International Seminar on Double Layer Capacitors and Hybrid Energy Storage Devices,vols.6–8,Deerﬁeld Beach,USA,December,2004,p.40.[43]M.R.Wagner,P.R.Raimann,A.Trifonova,K.C.Moeller,J.O.Besenhard,M.Winter,Electrochem.Solid-State Lett.7(2004)A201.。

直流溅射沉积纳米晶氧化镍薄膜及电化学性能(2)

ＮｉＯ结构中因没有可供“＋嵌Ａ．／脱出的通道，也无法与金属锂形成合金，一直认为不适合作为锂离子电池的阳极材料。最近，Ｐｏｉｚｏｔ等口４。报道了ＮｉＯ不仅能够和Ｌｉ发生可逆的电化学反应，而且经多次循环后仍可保持较高的比容量和良好的循环性能，从而倍受
作者简介：蔡羽（１９７７～），女，河南洛阳人，讲师，硕士，主要从事功能薄膜材料研究，发表论文１２篇，发明专利２项。
●
ｉ．旦 ≥ 而亡ｍ芒
２贸Ｊ图１Ｓｉ片上沉积的ＮｉＯ薄膜在不同退火温度下的ＸＲＤ图谱
Ｆｉｇ．１ＸＲＤｓｐｅｃｔｒａｏｆＮｉＯｔｈｉｎｆｉｌｍｏｎＳｉｓｕｂｓｔｒａｔｅ
ｂｅｆｏｒｅａｎｄａｆｔｅｒａｎｎｅａｌｉｎｇｉｎａｉｒ
２．２退火温度对薄膜形貌的影响图２给出了不锈钢基片上沉积的不同退火温度下
（ａ）４００℃（ｂ）５００℃（ｃ）６００℃（ｄ）７００℃
《金属热处理）２００ｓ年第３３卷第８期
６５
基片结合紧密；而经６００、７００ｏＣ退火后，不锈钢基片上
ＮｉＯ薄膜有不同程度的火条件不妥所致。
当升温速率或降温速率较快时，热膨胀引起的内应力
［２］赵胜利，文九巴．ＮｉＯ负极薄膜制备与电化学性能［Ｊ］．应用化学。２００６，２３：４９４４９７．
２．４电化学性能初步研究通过上述分析，５００℃退火的ＮｉＯ薄膜形貌、组成
和结构均较好。采用该温度下的薄膜在氩气氛保护的手套箱中装配成电池；其中ＮｉＯ薄膜为工作电极，高
［３］ＰｏｉｚｏｔＰ，ＬａｒｕｅｌｌｅＳ，ＧｒｕｇｅｏｎＳ。ｅｔａ１．Ｎａｎｏ．ｓｉｚｅｔｒａｎｓｉｔｉｏｎ
（３）５００℃退火条件下制得的ＮｉＯ薄膜组成和结
构较好，具有良好的电化学循环稳定性，有望成为高性能的全固态薄膜锂电池阳极材料。

Materials for electrochemical capacitors

Climate change and the decreasing availability of fossil fuels require society to move towards sustainable and renewable resources. As a result, we are observing an increase in renewable energy production from sun and wind, as well as the development of electric vehicles or hybrid electric vehicles with low CO2 emissions. Because the sun does not shine during the night, wind does not blow on demand and we all expect to drive our car with at least a few hours of autonomy, energy storage systems are starting to play a larger part in our lives. At the forefront of these are electrical energy storage systems, such as batteries and electrochemical capacitors (ECs)1. However, we need to improve their performance substantially to meet the higher requirements of future systems, ranging from portable electronics to hybrid electric vehicles and large industrial equipment, by developing new materials and advancing our understanding of the electrochemical interfaces at the nanoscale. Figure 1 shows the plot of power against energy density, also called a Ragone plot2, for the most important energy storage systems.

二维层状Ti3C2超级电容器电极材料的合成及优化

摘要超级电容器以其功率密度高、充电时间短以及循环稳定性良好等优势成为有应用前景的储能器件。

超级电容器作为一种储能器件，存储能量的能力在很大程度上取决于电极材料的性能。

Ti3C2Tx（Tx为表面活性基团）作为一种新型二维过渡金属碳/氮化物层状材料，已被证实是一种电化学性能优异的插层赝电容型超级电容器电极材料。

然而，目前Ti3C2Tx均由氢氟酸及各类含氟盐等刻蚀剂合成，因此刻蚀过程中不可避免地存在-F等表面基团。

研究表明这些基团团聚在Ti3C2Tx表面限制了它电化学性能，使其没有达到理论的比容量。

本工作首先通过HF和HCl/LiF刻蚀前驱体Ti3AlC2制备出具有丰富表面基团的Ti3C2Tx（HF-48、HF-72、HCl-6M和HCl-9M），经过XRD、SEM、和EDS 等表征发现，相较HF-48、HF-72和HCl-9M，HCl-6M的-F基团含量较低，层间距离较大。

利用循环伏安法(CV)、恒电流充电/放电(GCD)和电化学阻抗(EIS)等电化学测试手段对电极材料进行电化学性能研究，结果表明：在1M H2SO4电解液中HCl-6M的比容量达到303F g-1，明显高于HF-48、HF-72和HCl-6M的比容量（分别为：112F g-1、198F g-1、143F g-1）。

同时，HCl-6M的倍率性能和循环稳定性也最好，这主要是因为HCl-6M中-F含量较低，层间距较大，有利于离子的快速传输，且其氧化还原反应的可逆性强。

这些结果说明Ti3C2Tx的电化学性能主要受表面基团的含量和层间距大小的影响。

本文还探究了电解液对Ti3C2Tx电化学性能的影响，测试结果表明，在H2SO4电解液中其比容量远高于在KOH或Na2SO4电解液中的比容量，这是由于Ti3C2Tx在H2SO4电解液中会产生赝电容，是典型的插层赝电容材料。

以上研究结果为接下来的Ti3C2Tx的表面修饰奠定了基础。

本工作进一步通过修饰Ti3C2Tx的表面结构及增大层间距离来进一步优化其电化学性能。

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per kilogram. Although great efforts have gone into developing high-performance Li-ion and other advanced secondary batteries that use nanomaterials or organic redox couples4–6, ECs have attracted less attention until very recently. Because Li-ion batteries suffer from a somewhat slow power delivery or uptake, faster and higher-power energy storage systems are needed in a number of applications, and this role has been given to the ECs7. Also known as supercapacitors or ultracapacitors, ECs are power devices that can be fully charged or discharged in seconds; as a consequence, their energy density (about 5 Wh kg–1) is lower than in batteries, but a much higher power delivery or uptake (10 kW kg–1) can be achieved for shorter times (a few seconds)1. They have had an important role in complementing or replacing batteries in the energy storage field, such as for uninterruptible power supplies (back-up supplies used to protect against power disruption) and load-levelling. A more recent example is the use of electrochemical double layer capacitors (EDLCs) in emergency doors (16 per plane) on an Airbus A380, thus proving that in terms of performance, safety and reliability ECs are definitely ready for large-scale implementation. A recent report by the US Department of Energy8 assigns equal importance to supercapacitors and batteries for future energy storage systems, and articles on supercapacitors appearing in business and popular magazines show increasing interest by the general public in this topic.
REVIEW ARTICLE
Materials for electrochemical capacitors
Electrochemical capacitors, also called supercapacitors, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. The discovery that ion desolvation occurs in pores smaller than the solvated ions has led to higher capacitance for electrochemical double layer capacitors using carbon electrodes with subnanometre pores, and opened the door to designing high-energy density devices using a variety of electrolytes. Combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. The use of carbon nanotubes has further advanced micro-electrochemical capacitors, enabling flexible and adaptable devices to be made. Mathematical modelling and simulation will be the key to success in designing tomorrow’s high-energy and high-power devices.
Patrice Simon1,2 and Yury Gogotsi3
1Université Paul Sabatier, CIRIMAT, UMR-CNRS 5085, 31062 Toulouse
Cedex 4, France
2Institut Universitaire de France, 103 Boulevard Saint Michel,
75005 Paris, France
3Department of Materials Science & Engineering, Drexel University, 3141
ut Street, Philadelphia 19104, USA
e-mail: simon@chimie.ups-tlse.fr; gogotsi@
Several types of ECs can be distinguished, depending on the charge storage mechanism as well as the active materials used. EDLCs, the most common devices at present, use carbon-based active materials with high surface area (Fig. 2). A second group of ECs, known as pseudo-capacitors or redox supercapacitors, uses fast and reversible surface or near-surface reactions for charge storage. Transition metal oxides as well as electrically conducting polymers are examples of
Lithium-ion batteries were introduced in 1990 by Sony, following pioneering work by Whittingham, Scrosati and Armand (see ref. 3 for a review). These batteries, although costly, are the best in terms of performance, with energy densities that can reach 180 watt hours
Climate change and the decreasing availability of fossil fuels require society to move towards sustainable and renewable resources. As a result, we are observing an increase in renewable energy production from sun and wind, as well as the development of electric vehicles or hybrid electric vehicles with low CO2 emissions. Because the sun does not shine during the night, wind does not blow on demand and we all expect to drive our car with at least a few hours of autonomy, energy storage systems are starting to play a larger part in our lives. At the forefront of these are electrical energy storage systems, such as batteries and electrochemical capacitors (ECs)1. However, we need to improve their performance substantially to meet the higher requirements of future systems, ranging from portable electronics to hybrid electric vehicles and large industrial equipment, by developing new materials and advancing our understanding of the electrochemical interfaces at the nanoscale. Figure 1 shows the plot of power against energy density, also called a Ragone plot2, for the most important energy storage systems.