三维双金属硫化物Co_9S...用于增强钠离子存储（英文）_陈红.pdf

Cite this:NewCarbonMaterials,2023,38(3):510-521DOI:10.1016/S1872-5805(23)60731-0A bimetallic sulfide Co9S8/MoS2/C heterojunction in a three-dimen-sional carbon structure for increasing sodium ion storageCHENHong,MUJian-jia,BIANYu-hua,GAOXuan-wen*,WANGDa,LIUZhao-meng,LUOWen-bin*（Institute for Energy Electrochemistry and Urban Mines Metallurgy,School of Metallurgy,Northeastern University,Shenyang 110819,China）Abstract：Thesynthesisofhigh-rateandlong-lifeanodematerialsforsodiumionbatteries(SIBs)hasattractedmuchattention.However,theslowkineticsandlargeincreaseinvolumeofthebatteriesremainmajorproblems.Bothmetal-organicframeworksandMoS2haveshownpropertiessuitableforSIBs,makingresearchontheircompositesystemsanattractiveareaofresearch.Wereporttheformationofflower-likeCo9S8/MoS2/Ccompositesbyasimultaneousvulcanization-carbonizationprocessusingMoCl5astheMosourceanda2-methylimidazolecobaltsaltastheCoandCprecursoratdifferenttemperatures（600,700and800C）insub-limedsulfur.Theeffectoftheheterojunctiononthediffusionkineticswasanalyzedusingdensityfunctionaltheory.Theresultsin-dicatethattheelectronicstructureisdifferentattheinterfaceintheheterogeneousstructure,exhibitingtypicalmetallicpropertiesandbetterelectronicconductivity.Inaddition,theanodematerialCo9S8/MoS2/Csynthesizedat700Chadthemoststablestructureandbestelectrochemicalperformanceofthethreesamples.Notably,thedischargecapacityofCo9S8/MoS2/C-700fullyrecoveredfrom368to571mAhg1andthenstabilizedat543mAhg1whenthecurrentdensitywasrestoredfrom4000to40mAg1.Thisworkdemonstratesthepreparationofheterojunctionmaterialsforcompositeanodematerialsasasteptoproducinghigh-performancemet-alSIBs.Key words:Sodiumionbatteries；Anode；Metal-organicframe；MoS2；Co9S81IntroductionLithium-ionbatteries are now commonly em-ployed in portable consumer electronics gadgets aswellasemergingelectricvehicles12.However,themassiveriseoflithium-ionbatteries(LIBs)impliesajumpinlithiumresourceprices,aswellasalimitedandunevendistributionoflithiumreservesaroundtheglobe,limitingthedevelopmentofLIBs35.Duetotheirabundantmaterialsandsimilaritywithlithiumschemistry,sodium-ionbatteries(SIBs)havedrawnagreatdealofinterestandareconsideredcapableofpartiallyreplacingLIBs67.Transitionmetalsulfides(TMS)havereceivedagreatdealofattentionasan-odematerialsforSIBsduetotheirenormoustheoret-icalcapacityandhighsafety,aswellastheirhigherelectricalconductivityandfastercharge-dischargere-actionkineticsthanoxides.Amongrecentlyproducedanodematerials,MoS2isaclassicexampleofTMS,withsimplepreparation,abundantrawmaterials,highinterlayerspacing(0.62nm)andweakinterlayervanderWaalsforces811.TMSdoes,however,havesev-eral flaws.On one hand,TMS experiences severevolumeexpansionduringchargeanddischarge,caus-ingcyclestabilitytobepoor12.Ontheotherhand,al-thoughthanoxides,TMShavegenerallylowercon-ductivitywhichcausesdelayedelectrochemicalreac-tionkineticsandresultsininadequaterateperform-ance1314.Theconstruction of heterogeneous metal sulf-idesisaneffectivemethodforaddressingthedraw-backoflowelectricalconductivity1516.Whencom-pared to single-phase metal sulfides,heterogeneousmetalsulfidescannotonlypromotethecreationofaninternalelectricfield,butalsoenhancetheactivityofelectrochemicalreactions at the heterointerface,in-Received date：2023-01-05；Revised date：2023-02-28Corresponding author：GAOXuan-wen,AssociateProfessor.E-mail:;LUOWen-Bin,Professor.E-mail:Author introduction：CHENHong,Ph.Dcandidate.E-mail:Supplementarydataassociatedwiththisarticlecanbefoundintheonlineversion.第38卷第3期新型炭材料（中英文）Vol.38No.32023年6月NEWCARBONMATERIALSJun.2023creasing electrical conductivity1719.It can also im-provecrystallinityattheheterointerface,aswellasin-ducelattice mismatches,distortions and defects,al-lowingthereactionkineticsofelectrodematerialstobe tuned2022.Due to the continuous insertion andconversion/alloying reaction in SIBs,there is rapidvolume change of electrode materials.To solve theaboveproblems,porousnanostructureengineeringcanbeconstructedtoimprovethestabilityofsodiumstor-ageperformanceofmixedmetalsulfides.Metal-organicframeworks(MOFs),asporousin-organic-organic hybrid materials with high specificsurfacearea,controllablestructure,andtunableporesize,arewidelyusedasprecursorsforthepreparationofcarbon-metalormetalsulfidecomposites2325.Ingeneral,MOFsexhibitimpressiveperformanceasact-ivematerialsforenergystorageduetotheircomplexandvariedstructuraladvantages2628.Moreover,thenanostructureofMOFscannotonlyshortenthediffu-sionpathofNaions,butalsowithstandthevolumeexpansioncausedbytheinsertionofNaions,provid-ingastablesupportfortheoverallstructure2829.Withtheaimofovercomingtheweaknessesofany single component,in this work,a flower-likeCo9S8/MoS2/Ccompositewasdesignedandconstruc-ted by a simultaneous vulcanization-carbonizationmethodatdifferenttemperaturesusingCo-ZIFaspre-cursorandaddingMosource.Bysystematicallyin-vestigatingtheeffectofsulfurvacanciesandmicroto-pography on sodium storage behaviour,the flower-likeCo9S8/MoS2/Cmicrospheresformedbyintercon-nectednanosheetarrays(Co9S8/MoS2/C-700)possessthebestelectrochemicalperformance.Heterogeneousmetalsulfidescannotonlyenhancetheelectricalcon-ductivityoftheelectrodematerialduetothehetero-structure,but also facilitate electron/ion transport.Most importantly,the spherical structure provides astablesupportandtheporousstructureprovidesabuf-ferspaceforthevolumedeformationcausedbysub-sequentredoxreactions.Itisworthnotingthatthedis-chargecapacityofCo9S8/MoS2/C-700canfullyrecov-er from 368 to 571 mAh g1 and then stabilize at543mAhg1whenthecurrentdensityisrestoredfrom4000to40mAg1.2Experimental 2.1 Materials synthesisZIF-67wassynthesizedbyaroomtemperatureprecipitationmethod that has been reported previ-ously30.Typically,Co(NO3)26H2O(5.82g,0.02mol)and 2-MeIm(6.16 g,0.075 mol)were dissolved in150mLofmethanoltoformclarifiedliquor.Then,thesolutionof2-MeImmixturewaspouredintothesolutionofCo(NO3)26H2Oandstirredevenlyatroomtemperaturefor24h.Finally,thepurpleZIF-67wasobtainedbycentrifugingthemixtureandwashingsev-eral times with methanol and drying at 60 Covernight.20mgoftheaboveZIF-67templatewasdisper-sed in 40 mL CH3OH to form a uniform solution.Then 1.5 mL MoCl5(0.2 mol L1)solution and0.1664gofNH4HCO3weresuccessivelyaddedtothesuspension.Aftermagneticstirringfor7h,thebrownprecipitate was collected by centrifugation,washedthree times with deionised(DI)water,and dried at60Covernight.Co9S8/MoS2/C-700wasfabricatedbyasimultan-eous vulcanization-carbonization method.0.02 g ofas-preparedMo-based precursor and 0.05 g of sub-limedsulphurwereuniformlymixedandplacedinthecentreofaquartztube.Afterrinsingwithhigh-purityargon,thefurnacewasheatedto700Cataheatingrate of 5 C min1 and maintained for 1 h under aH2/Ar(90%v/v)mixedatmosphere.Forcomparison,thesamplesofCo9S8/MoS2/C-600andCo9S8/MoS2/C-800werealsosynthesizedinthesamemannerunderthesameconditionsexceptthecalcinationtemperaturewas600Cand800C,re-spectively.2.2 Materials characterizationThephasecompositionsoftheZIF-67templateandCo9S8/MoS2/C-700,600,800wereanalysedbyX-ray diffraction(XRD)(Deutschland BRUKER D8)usingCu-Kradiation.Scanningelectronmicroscopy(SEMSU8220,HitachiHigh-TechCompany),high-resolutiontransmissionelectronmicroscopy(HRTEM)第3期CHENHongetal:AbimetallicsulfideCo9S8/MoS2/Cheterojunctioninathree-dimensionalcarbon511andasuper-XEDSdetectorsystem(Bruker,Super-X,USA)wasusedtoexaminethemorphology,micro-structureofthesamplesandenergydispersivespec-trometry(EDS)elementalmaps.X-rayphotoelectronspectroscopy(XPS,ThermoESCALAB250XIAlKX-raysource)wereusedtoanalyzeelementalchemic-alcompositionsofmaterial.2.3 Electrochemical measurementsThe as-obtained active material,carbon black,and sodium carboxymethyl cellulose(CMC)weremixedwithDIwaterinaweightratioof721toformaslurry,andcoatedonCufoil.Thecoatedfoilwasdriedat80Cinvacuumovernightandcutintodiscswithadiameterof12mm.Glassfiberwasusedas the separator and metallic sodium was used ascounterelectrodeforSIBs.1.0molL1NaClO4dis-solved in EC/DMC(11,volume ratio)with FEC(5%,mass fraction)was used as electrolyte.Theaboveworkingelectrode,glassfiber,electrolyteandcounterelectrodeswereassembledinagloveboxofAratmospheretoobtainthehalf-cells.Thechargeanddischarge test measurement was carried out in thevoltagerangeof3.0-0.01VversusNa/Na+atroomtemperature(25 C)using LAND CT2001A testingsystem.Cyclicvoltammetry(CV)testswereconduc-tedonanLANHEM340Ainstrumentelectrochemic-al workstation between 0.01 and 3.0 V vs.Na+/Nawiththestatedscanrates.Electrochemicalimpedancespectroscopy(EIS)wascarriedoutonthePrinceton2273atfrequenciesof100kHzto10MHz.2.4 Density functional theory calculationThedensityfunctionaltheory(DFT)calculationswereperformedusingtheViennaAbinitioSimula-tion Package(VASP)3132.The Perdew-Burke-Ernzerhof(PBE)functionalgeneralizedgradientap-proximation(GGA)was considered to describe theexchange-correlation.The kinetic energy cutoff fortheplanewavewasabout520eV,whichwasappliedforthewavefunctionexpansionofS,MoandCo.Inaddition,Brillouinzoneintegrationonthegridwitha333and12121kgridmeshwascarriedouttoachievegeometryoptimizationandcalculationofthedensityofstates(DOS),respectively.TheMoandCoatomsusetheDFT+Utechnique,wheretheUJparametersforMoandCostatesaresettobe5.5and3.32eV,respectively.Thequasi-Newtonmethodwithenergyandforceconvergencecriteria,andtheNew-tonmethodwithenergyandforceconvergencecriter-iaof1.0106eVperatomand0.01eV1inthestructuraloptimizationwereperformedforMoS2andCo9S8toobtainhighaccuracy.ThevanderWaalsin-teraction force was analyzed with a semi-empiricalDFT-D3method.Virtualinteractionwasavoidedbyapplyinga15vacuumlayerthickness.3Resultsanddiscussion 3.1 Structure and compositionThe synthesis process of the flower-likeCo9S8/MoS2/Cnanocomposite is schematically illus-tratedinFig.1a.TheuniformZIF-67nanocrystalpre-cursorwasgeneratedbyasolvothermaltechnique,asevidenced by scanning electron microscopy(SEM)image(Fig.S1a).Then,molybdenum pentachloridewasaddedtothesolutioncontainingZIF-67precurs-orasamolybdenumsourcetoobtainauniformmo-lybdenumprecursor.Finally,becausetheelectroneg-ativityofCo(1.9)isslightlyhigherthanthatofMo(1.8),CoandMoionswillreactwithsulfurpowderathightemperaturetoformCo9S8,andthencausetheheterogeneous nucleation and subsequent growth ofMoS2nanoparticlesonthesurfaceofCo9S8.The crystal structure of as-synthesized samplewas studied by X-ray diffraction(XRD).The XRDpattern of the Co9S8/MoS2/C composite prepared atdifferenttemperatures(600,700,800C)areshowninFig.1b.Asexpected,allsamplesshowsimilardif-fraction patterns.There are a series of diffractionpeaks around 14.1,32.5,58.1 and 60.1,whichshould be indexed to the(002),(101),(103),(110)and(008)planesoftheMoS2(JCPDSNo.75-1539).Andotherpeaksat29.6and51.2canalsobeob-served,which match well with the(311)and(440)planesofcubicCo9S8(JCPDSNo.86-2273).TheseprovetheformationoftheMoS2andCo9S8phasesinthepolyhedralstructures.Additionally,thereisnodif-fraction peak of S in the image.The XRD resultsshowthehighpurityofthesynthesizedsample.512新型炭材料（中英文）第38卷SEMandTEMwereusedtoinvestigatethemor-phologyandmicrostructureofthematerial.ItcanbeclearlyseenfromFig.S1athattheZIF-67precursorisaregularpolyhedron.Inaddition,thepreparedZIF-67isauniformpolyhedronofsimilarsizeasshowninFig.S1b.InFig.S1c-dandFig.1c,thesmoothsur-faceofZIF-67iscompletelycoveredbyalargenum-ber of folds,which are composed of vertical andcross-linkedarraysofMoS2nanosheets.Toincreasethedegreeofcrystallinityintheproduct,thecalcina-tiontemperatureis600-800C.Inaddition,thesepre-pared nanosheets are also connected to each other,providing abundant open spaces and active sites,formingatypicallooseandporousarchitecturalstruc-ture.AscanbeseenfromFig.S2,withthegradualin-creaseoftemperature,thecrystallinityofthematerialincreasesandthereispartialcollapseonthesurface.Whenthetemperaturewasincreasedto800C,thedegree of crystallization increased and the shape ofthe resulting Co9S8/MoS2/C-800 microspheres wasdistorted,andduetothecollapseoftheactivemateri-alathighertemperatures,manynanosheetswereir-regularly aggregated.This would greatly reduce theprobabilityofioninsertionandextraction.Consider-ingtheinfluenceoftemperatureoncrystallinityandelectrochemical properties,Co9S8/MoS2-700 couldachievefarsuperiorperformancethanothersamples,andwillbediscussedinthefollowingsection.Togainfurtherinsightintothecompositionandmicrostruc-tureoftheCo9S8/MoS2/C-700,theelementmappingspectraandTEManalyseswereperformed.TheTEMimage(Fig.1d-e)revealed the intimate contactbetweenMoS2nanoparticlesandtheCo9S8substrate.Theabundanthetero-interfacecreatedmayactasact-ivesitesforfastNa+storage33.Fig.1dshowsMoS2nanosheets with approximately 7 atomic layersformedonaporousskeletonsubstrate.InFig.S3(a-b)，the lattice spacing of MoS2 and were 0.678 nm(a)(b)(c)(f)(g)(h)(i)(j)(k)CoMoSNC10 nm200 nm10 nm10 nmd=0.678 nmd=0.275 nmd=0.294 nm(0 0 2)MoS2(1 0 3)Co9S8(3 1 1)d=0.191 nmCo9S8(5 1 1)7 layer6 layer(d)(e)MoCl5StirringZIF-67MoSCoMo-precursorCo9S8/MoS2CalcinationS sourceTopSide102030405060708090Intensity/a.u.2/()2H-MoS2(JCPDS NO.37-1492)Co9S8/MoS2-800Co9S8/MoS2-700Co9S8/MoS2-600(002)(101)(103)(006)(105)(311)(440)(110)Co9S8(JCPDS NO.86-2273)Fig.1(a)Schematicillustrationoftheflower-likeCo9S8/MoS2/Cheteroball.(b)XRDpatternsZIF-67precursorandCo9S8/MoS2/Csynthesizedat600C,700C,800C.(c)SEMimageand(d,e)HRTEMimageofCo9S8/MoS2/C-700.(f-k)EDSmappingimagesoftheflower-likeCo9S8/MoS2/C-700hetero-ball第3期CHENHongetal:AbimetallicsulfideCo9S8/MoS2/Cheterojunctioninathree-dimensionalcarbon513(002)and 0.275 nm(103),and Fig.S3c shows the(311)planeofrutileCo9S8correspondingtothelat-ticefringeof0.294nm.FromFig.1(f-k),theS,MoandCoelementsareuniformlydistributedthroughoutthewholemicrosphere.X-rayphotoelectronspectroscopy(XPS)analys-iswasthenconductedtoinvestigatethesamplesandbinding states of each element.Fig.S4a shows thesurveyspectrumoftheCo9S8/MoS2/C-700hetero-ball.ThesurveyXPSspectrumtestifiestheexistenceofC,N,Mo,Co,OandSelements.Fig.S4bdepictstheC1sspectrumfittedinto3peaksatbindingenergiesof284.8,286.4and288.8eV,whichshouldberelatedtotheCC,CN/OandCObonds,respectively34.IntheMo3dspectrum(Fig.2a),thetwomajorpeaksat232.0and229.1eVareingoodagreementwithMo3d3/2 and Mo 3d5/2 of Mo4+,further confirming theformationofMoS2inthesimple.Thepeakat226.3isassignedtoS2s35.Meanwhile,thetwoweakpeakslocatedat236.0eVareattributedtotheMo6+becauseofslightsurfaceoxidation36.Thehigh-resolutionCo2pspectrumexhibitssixmainpeaksat778.9,782.6,786.9,794.1,798.7and804.6eV(Fig.2b).Amongthem,thebindingenergiesat778.9and794.1eVcor-respondtoCo2p3/2andCo2p1/2,andthe2satellitepeaksat804.6and786.9eVcanbeattributedtothetypical peaks for Co3+.Strong peaks at 782.6 and798.7eVcouldbeattributedtoCo2p3/2andCo2p1/2ofCo2+37.For the N 1s core-level XPS spectrum ofCo9S8/MoS2/C-700(Fig.2c),4 peaks can be fitted,correspondingtoMo3p(394.9eV)and3differenttypesofNspecies,wheretheNspeciesarepyridine(398.7 eV),pyrrole(400.1 eV)and graphite(401.0eV)38.ThereasonofthesamplecontainingNisthattheorganicligand(2-MIM)richinnitrogenisdecom-posedintheprocessofhightemperaturecalcination.Itisfoundthatpyridinenitroge