具有类混凝土结构的SiOx-C锂离子电池复合材料的制备.pdf

采用一种简单的方法制备具有类钢筋混凝土结构的SiOC负极材料，其中碳纳米管(carbon nanotubes，CNTs)如同钢筋一般嵌入材料中以提供应力支撑，硅原子被原子级分散的碳和氧原子均匀包裹，最后通过化学气相沉积镀上最外层的碳层，进一步抑制材料的体积变化。基于此独特的结构设计制备的CNTs/SiOxC/C负极表现出优异的电化学性能，其在0.5 Ag-1的电流密度下循环970圈后容量保留率为80%。关键词：SiOx；碳纳米管；碳层包覆；负极；锂离子电池中图分类号：TB33文献标识码：A文章编号：10014861(2023)09176609DOI：10.11862/CJIC.2023.144Preparation of SiOxC composite materials with a reinforcedconcretelike structure for lithiumion batteriesMA JinYangXU YaNanZHANG YuDU HongBin(State Key Laboratory of Coordination Chemistry,School of Chemistry and Chemical Engineering,Nanjing University,Nanjing 210093,China)Abstract:This work reports a simple method to prepare a SiOC anode material with a reinforced concretelikestructure,in which carbon nanotubes(CNTs)were embedded and acted like steel bars to provide stress support,andthe silicon atoms were wrapped with atomically dispersed carbon and oxygen concrete matrix.An outermost carbonlayer was plated via chemical vapor deposition to further inhibit the volume change of the material.Thanks to theunique structural design,the prepared CNTs/SiOxC/C anode showed excellent electrochemical performance with ahighcapacity retention rate of 80%after 970 cycles at 0.5 Ag-1.Keywords:SiOx;carbon nanotube;carbon coating;anode;lithiumion battery0IntroductionGraphite is the mainstream anode material for lithiumion batteries(LIBs),but it is slowly failing to meetthe needs of highperformance LIBs due to its low theoretical capacity(372 mAhg-1).Although siliconbasedmaterials have a high theoretical capacity,their hugevolume expansion(ca.300%)in the process of chargeand discharge greatly reduces the cycling performanceand hinders its marketization process12.In comparison,silicon oxide(SiOx,0 x2)had attracted wideattention because of its higher theoretical capacity thangraphite and smaller volume expansion than elementalsilicon,which is a promising anode material for thenext generation of LIBs34.To alleviate the volume expansion of Si basedmaterials,researchers have developed several solutions,such as coating siliconbased nanomaterials withcarbon or oxides(such as SiO25,TiO26),or preparation第9期of siliconbased nanomaterials with specific morphology.For example,Li et al.coated SiOxnanoparticleswith carbon formed by asphalt pyrolysis7.Yang et al.constructed amorphous TiO2shells by a facile solgelapproach to adapt to the volume change of silicon based material8.Li et al.introduced silicon basedmaterials onto carbon nanotubes by chemical vapordeposition(CVD)using silane gas as a silicon source9.Sun et al.prepared ultrathin SiOxnanosheets by solvothermal stripping of CaSi210.Furthermore,researchersalso found that coated Sibased materials in atomic sizewere a better choice compared to conventional nanosized coating.For instance,Zhou et al.prepared atomically homogeneous SiOx/C hollow spheres by a onepotaldimine condensation for LIB anodes,realizing therequirements of atomiclevel coating and special morphology of materials at the same time11.Herein,we report the preparation of a compositeSiOC material(named CNTs/SiOxC/C)with a reinforced concretelike structure,in which carbon nanotubes(CNTs)are embedded in the material like steelbars to provide stress support inside the material.Atomically dispersed carbon and oxygen atoms encasethe silicon atoms as a buffer matrix.A carbon protection layer was further coated onto the outer layer of thematerial by CVD to fully mitigate the expansion effectof the material.As a result,the prepared compositematerial delivered stable cycle performance with acapacity retention rate of 80%after 970 cycles at a current density of 0.5 Ag-1.1Experimental1.1MaterialMultiwalled CNTs were acquired from XianfengNano Co.,Ltd.3Aminopropyltriethoxysilane(C9H23NO3Si,APTES,98%)was purchased from Bide Co.,Ltd.Ammonium hydroxide(NHHO)was purchased fromSinopharm Chemical Reagent Co.,Ltd.Dichloromethane(CH2Cl2)was purchased from Sinopharm ChemicalReagent Co.Ltd.,and was dried over CaH2before use.1.2Fabrication of CNTs/SiOxC and CNTs/SiOxC/CIn a typical procedure,100 mg of CNTs were firstdispersed in 15 mL of CH2Cl2.2 mL of NHHO wasadded into the above solution and stirred for 10 minutes.Then,2 mL of APTES was added dropwise.Afterstirring at room temperature overnight,the solution wasleft to stand and stratified rapidly.The solid wasobtained by centrifugation,which was then put intotube finance and heated at 900 for 2 h with a ramping rate of 5 min-1under Ar atmosphere to obtainCNTs/SiOxC.To coat CNTs/SiOxC with carbon,theproduct CNTs/SiOxC was further heated under a toluene atmosphere at 800 for 2 h.For comparison,reference materials named CNTs/SiOxC800 and CNTs/SiOxC1000 were prepared following the same procedure as CNTs/SiOxC,but pyrolysis temperature set at 800 and 1 000,respectively.ReferencematerialsnamedCNTs/SiOxC2.5andCNTs/SiOxC1.5 were prepared following the same procedure as CNTs/SiOxC,but the dosage of APTES was2.5 and 1.5 mL,respectively.1.3Material characterizationsThe powder Xray diffraction(PXRD)patterns ofthe prepared materials were recorded on a Bruker D8Xray diffractometer(Cu K radiation,=0.154 18 nm,2=1080,operated at 40 kV and 40 mA).Scanningelectron microscope(SEM,Hitachi S4800 electronmicroscope,20 kV)and transmission electron microscope(TEM,JEM 2100 microscope,200 kV)wereused to investigate the morphologies of all materials.X ray photoelectron spectroscopy(XPS,PHI 5000VVersaProbe spectrometer)was used to investigate thesurface composition of the materials.The Raman spectra of the materials were obtained on a LabRAMAramis Raman spectrometer(Horiba,488 nm laser).The thermogravimetric analysis(TGA)was performedon a Netzche STA449F3 from 30 to 960 under flowing air with a heating rate of 10 min-1.1.4Electrochemical characterizationsThe working electrode was composed of activematerial(Mass fraction:70%),sodium alginate(Massfraction:20%),super P(Mass fraction:10%),and copper foil as a current collector,and lithium sheets wereused as counter electrodes.The load mass of the activematerial of all electrodes was about 0.81.2 mgcm-2马晋杨等：具有类混凝土结构的SiOxC锂离子电池复合材料的制备1767无机化学学报第39卷after drying at 80 for 500 min under vacuum.Thecoin cells(CR2032type)were assembled in an argonfilled glovebox(H2O,O2contents were below 10-7cm3cm-3).Celgard 2400 membrane was used as a separator.1 molL-1LiPF6in ethylene carbonate/dimethylcarbonate/diethyl carbonate(EC/DMC/DEC,1 1 1 involume)was used as an electrolyte.Galvanostatic charge discharge(GCD)measurements were carried out on a Neware battery testingdevice(Shenzhen,China)with a voltage window of0.012 V(vs Li/Li+).Cyclic voltammetry(CV)with avoltage window of 0.012 V(vs Li/Li+)and a scan rateof 0.1 mVs-1.Electrochemical impedance spectroscopy(EIS)with a frequency range from 0.01 Hz to 100kHz was conducted on an electrochemical station(CHI650D,Shanghai Chenhua Instruments Inc.,China).2Results and discussionFig.1 shows the preparation process for the material studied in this work.The commercial CNTs wereused as hard templates,which were coated by inorganic and organic hybrid network structures with the atomic distribution of Si,C,and O elements through hydrolysis reaction of APTES under alkaline conditions.After calcination in inert atmosphere,composite CNTs/SiOxC was obtained.Finally,the outer carbon layer ofthe material was introduced via CVD to obtain CNTs/SiOx C/C.In this designed composite material,theinternal CNTs acted as an internal skeleton,andworked together with the outermost carbon layer to relieve the volume change of the siliconbased materialduring the processes of charge and discharge.On theother hand,the atomically dispersed carbon and oxygen atoms formed a buffer matrix to engage siliconatoms,which also relieved the volume expansion stressfrom inside the material.Fig.2a,2d,and Fig.S1(Supporting information)depict the SEM images of CNTs/SiOxC and CNTs/SiOxC/C,respectively.In comparison,there were moreexposed CNTs on the outer surface of CNTs/SiOx C,and CNTs/SiOx C/C treated with CVD had a flatterouter surface.TEM images in Fig.2b and 2e show thatCNTs/SiOx C and CNTs/SiOx C/C both had CNTsembedded in the amorphous material and CNTs/SiOxC/C had a thin outer layer of carbon.High resolutionTEM(HRTEM)images of the two materials in Fig.2cand 2f show the lattice spacing of 0.34 nm corresponding to the(002)lattice plane of graphitic CNTs(PDFNo.411487)1214.Fig.2g depicts the TEM elementalmapping images of CNTs/SiOxC,showing unevenly distributed Si,O,and C elements,with CNTs exposed outside the bulk material.On the other hand,the TEM elemental mapping images of CNTs/SiOxC/C in Fig.2hshow that the C element was more widely distributedthan the Si and O element,which could be contributedto the outermost carbon layer formed by CVD.In addition,the Si,O,and C elements were found evenly distributed,suggesting the formation of atomically dispersed SiOxC composite material.The PXRD patterns of CNTs/SiOxC/C and CNTs/SiOx C show the broad peaks between 20 and 35belonging to amorphous SiOx(Fig.3a)1516.As shown inFig.1Schematic diagram of the preparation processes for CNTs/SiOxC and CNTs/SiOxC/C1768第9期Fig.3b and Fig.S2,both TG curves of CNTs/SiOxC/Cand CNTs/SiOxC had a big drop from 600 to 800,which is mainly due to the combustion loss of carbonmaterials when heated in air(CNTs/SiOxC/C:37.77%,CNTs/SiOx C:31.63%).The mass fraction of Si element in CNTs/SiOxC and CNTs/SiOxC/C were 31.9%and 29.0%,respectively.Raman spectra were used toinvestigate the existence and crystalline state of carbon.As shown in Fig.3c and 3d,both samples displayed two strong peaks at around 1 330 and 1 610cm-1,attributed to the Dband and Gband of carbonmaterial,respectively17.The Dband is related to thecarbon atoms with dangling bonds at the edges and/ordefects of the graphite carbon,while the G band isassociated with the sp2hybridized carbon atoms18.Thestrong G band and small relative intensity ratio of thetwo bands(ID/IG)imply that both samples were highlygraphitized19.In comparison,CNTs/SiOx C/C had asmaller ID/IGratio of 0.485 than that of CNTs/SiOx C(0.519),illustrating that the graphitization quality ofCNTs/SiOxC/C is higher.Fig.4a and 4d show XPS spectra of CNTs/SiOxCandCNTs/SiOxC/C,respectively.Incomparison,CNTs/SiOxC/C showed a stronger C1s peak and weaker O1s peak than CNTs/SiOxC,which could be attributed to the carbon protective layer in CNTs/SiOx C/Cintroduced by CVD with toluene as carbon source.TheSi2p XPS spectra of CNTs/SiOxC and CNTs/SiOxC/Cboth displayed peaks around 103 eV(Fig.4b,4e),which could be deconvoluted into three peaks at 102.3,103.1,and 103.8 eV in CNTs/SiOxC(Fig.4b),and at102.0,102.7,and 103.5 eV in CNTs/SiOxC/C(Fig.4e)owing to Si2+,Si3+,and Si4+,respectively2021.The C1sXPS spectra of CNTs/SiOxC(Fig.4c)and CNTs/SiOxC/C(Fig.4f)could be deconvoluted to the sp2C(283.6eV),sp3C(284.4 eV),CCO(285.5 eV),and COOCFig.2(a)SEM,(b)TEM,and(c)HRTEM images of CNTs/SiOxC;(d)SEM,(e)TEM,and(f)HRTEM images ofCNTs/SiOxC/C;TEM mapping images of(g)CNTs/SiOxC and(h)CNTs/SiOxC/C马晋杨等：具有类混凝土结构的SiOxC锂离子电池复合材料的制备1769无机化学学报第39卷Fig.3(a)PXRD patterns of CNTs/SiOxC/C,CNTs/SiOxC,and pure CNTs;(b)TG curve of CNTs/SiOxC/C;Raman spectra of(c)CNTs/SiOxC and(d)CNTs/SiOxCFig.4XPS spectra of(ac)CNTs/SiOxC and(df)CNTs/SiOxC/C:(a,d)full spectra;(b,e)Si2p region;(c,f)C1s region1770第9期(288.5 eV)(Fig.4c),sp2C(283.6 eV),sp3C(284.5 eV),CCO(285.8 eV),and COOC(288.8 eV)(Fig.4f),respectively22.The high intensities of the sp2C peaksimply high graphitization quality in both materials,while weaker relative intensities of the oxygenbindingC peaks in CNTs/SiOxC/C are due to the CVD carbonlayer on the particle surface.Fig.5a and 5b show the GCD curves of CNTs/SiOxC and CNTs/SiOxC/C electrodes at the current densityof 0.1 Ag-1with a potential window from 0.01 to 2 V.Both curves showed irreversible capacity change aftercomparing the discharge charge curve of the first circle,which are consistent with their CV curves(Fig.S3).The GCD results illustrated that CNTs/SiOxC andCNTs/SiOxC/C electrodes both had relatively low initial coulombic efficiency(both were about 50%),whichmainly could be contributed to the formation of thesolidelectrolyte interphase(SEI)layer and side reactions2324.Fig.5c and 5d show the rate performance ofCNTs/SiOxCandCNTs/SiOxC/Celectrodes.TheCNTs/SiOxC electrode delivered specific charge capacities of 662,573,488,395,and 330 mAhg-1at thecurrent densities of 0.1,0.2,0.4,0.8,and 1.2 Ag-1,respectively.On the other hand,the CNTs/SiOxC/Celectrode displayed specific charge capacities of 620,527,434,345,and 278 mAhg-1at the current densities of 0.1,0.2,0.4,0.8,and 1.2 Ag-1,respectively.Both electrodes recovered after the current densitychanged back to 0.1 Ag-1,with a highcapacity retention of 86.0%(569 mAhg-1)for CNTs/SiOxC electrode and 94.4%(585 mAhg-1)for CNTs/SiOxC/Celectrode.It is noted that the pure CNTs electrode prepared under similar conditions had a charge capacityof 280 mAhg-1at 0.1 Ag-1(Fig.S4),suggesting thatthe specific capacities of CNTs/SiOxC and CNTs/SiOxC/C are mainly due to SiOxspecies.Fig.5d shows the effects of different dosage ratiosof APTES and CNTs on the electrochemical propertiesof electrode materials.The CNTs/SiOxC electrodedelivered a reversible capacity of about 681 mAhg-1,and a capacity retention rate of 80%after 700 cycles at0.5 Ag-1.In comparison,the charge capacity the ofCNTs/SiOxC2.5 electrode was 771 mAhg-1,and thecapacity retention rate was 68.7%at the 700th cycle,Fig.5GCD profiles of(a)CNTs/SiOxC and(b)CNTs/SiOxC/C electrodes for the first three cycles at 0.1 Ag-1;(c)Rate performance of CNTs/SiOxC and CNTs/SiOxC/C electrodes;(d)Longterm cycling performanceof the CNTs/SiOxC,CNTs/SiOxC2.5,CNTs/SiOxC1.5 electrodes;(e)Longterm cycling performance ofthe CNTs/SiOxC,CNTs/SiOxC1000,CNTs/SiOxC800 electrodes;(f)Longterm cycling performance ofCNTs/SiOxC/C electrode马晋杨等：具有类混凝土结构的SiOxC锂离子电池复合材料的制备1771无机化学学报第39卷the CNTs/SiOx C 1.5 electrode showed a reversiblecapacity about 605 mAhg-1and a capacity retentionrate 92.4%at 700th cycle.Fig.5e shows the longtermcycling performance of CNTs/SiOx C electrode,compared with those of CNTs/SiOxC1000 electrode andCNTs/SiOxC800 electrode prepared at different pyrolysis temperatures.The cycling performance of CNTs/SiOxC was better than the CNTs/SiOxC1000(74%)and CNTs/SiOxC800(79%)electrodes.The resultssuggest that the pyrolysis temperature of 900 wasoptimal for the material preparation.The poorer performance of the materials prepared at lower or higher temperatures might be due to less graphitized carbon orlower surface area due to sintering.In comparison,theCNTs/SiOxC/C electrode delivered a capacity retentionrate of 80%after 970 cycles at 0.5 Ag-1(Fig.5f),better than the CNTs/SiOxC electrode.The SEM images of CNTs/SiOx C and CNTs/SiOx C/