采用两步炭化法和熔盐模板法制备N、S共掺杂煤基硬炭及共储钠性能.pdf

Cite this:NewCarbonMaterials,2024,39(2):297-307DOI:10.1016/S1872-5805(24)60842-5N,S co-doped coal-based hard carbon prepared by two-step carboniz-ation and a molten salt template method for sodium storageNIUHui-zhu1,WANGHai-hua1,2,3,*,SUNLi-yu1,YANGChen-rong1,WANGYu4,CAORui1,YANGCun-guo1,WANGJie1,SHUKe-wei1,*（1.School of Chemistry and Chemical Engineering,Shaanxi University of Science and Technology,Xian 710021,China;2.Xian Key Laboratory of Advanced Performance Materials and Polymers,Shaanxi University of Science and Technology,Xian 710021,China;3.Shaanxi Key Laboratory of Chemical Additives for Industry,Shaanxi University of Science and Technology,Xian 710021,China;4.Xian North Huian Chemical Industry Co,Xian 710302,China）Abstract：Hardcarbon,knownforitsabundantresources,stablestructureandhighsafety,hasemergedasthemostpopularan-odematerialforsodium-ionbatteries(SIBs).Amongvarioussources,coal-derivedhardcarbonhasattractedextensiveattention.Inthiswork,NandSco-dopedcoal-basedcarbonmaterial(NSPC1200)wassynthesizedthroughacombinationoftwo-stepcarboniza-tionprocessandheteroatomdopingusinglong-flamecoalasacarbonsource,thioureaasanitrogenandsulfursource,andNaClasatemplate.Thetwo-stepcarbonizationprocessplayedacrucialroleinadjustingthestructureofcarbonmicrocrystalsandexpandingtheinterlayerspacing.TheNandSco-dopingregulatedtheelectronicstructureofcarbonmaterials,endowingmoreactivesites.Ad-ditionally,theintroductionofNaClasatemplatecontributedtotheconstructionofporestructure,whichfacilitatesbettercontactbetweenelectrodesandelectrolytes,enablingmoreefficienttransportofNa+andelectrons.Underthesynergisticeffect,NSPC1200exhibitedexceptionalsodiumstoragecapacity,reaching314.2mAhg1at20mAg1.Furthermore,NSPC1200demonstratedcom-mendablecyclingstability,maintainingacapacityof224.4mAhg1evenafter200cycles.Thisworksuccessfullyachievesthestra-tegictuningofthemicrostructureofcoal-basedcarbonmaterials,ultimatelyobtaininghardcarbonanodewithexcellentelectrochem-icalperformance.Key words:Hardcarbon；Sodium-ionbattery；Coal-derivedcarbon；Two-stepcarbonization；NandSco-doped1IntroductionLithium-ion batteries(LIBs)stand as the mostwidelyusedsecondarybatteriesinenergystoragesys-tems.However,limitedresourcesofLianditschal-lengingextractionprocesseshaveconstrainedfurtherdevelopmentsinLIBs.Sodium,ontheotherhand,isnot only abundantly available and inexpensive butalsoshows similar chemical properties to lithium,makingsodiumionbatteries(SIBs)standoutasavi-talsupplementorpotentialsubstituteforLIBsinre-searchandindustrialization13.However,thedevel-opmentandapplicationofelectrodesinSIBsareintheearlystages.GraphiteisusuallyusedastheLIBsanode,butitisnotsuitableforSIBsduetothelargerionicradiusofsodium45.Therefore,findingsuitableelectrodematerialsiscrucialforthefuturedevelop-mentofSIBs.Researchershaveexploredvariousanodemateri-alsfor SIBs,each accompanied by its set of chal-lenges.Common alloying reaction anode materials,such as Na-P6,Na-Ge7 and Na-Sb8,exhibit highspecific capacity.However,these materials undergovolumeexpansionduringtheintercalationandde-in-tercalationprocessesofNa+,resultinginfasterspecif-iccapacitydecayandreducedcyclingperformance.Carbonmaterialsbasedonintercalationreaction,suchas graphene,hard and soft carbon,are significantlyadvantageousconsideringtheirlowcost,highstabil-ityandotheraspects910.Therefore,carbonmaterialscontinuetobethemainstreamchoiceforanodesinSIBs.Amongthem,coalanditsby-productspresentawiderangeofoptionsandhighcarboncontent,mak-Received date：2023-12-04；Revised date：2024-01-27Corresponding author：WANGHai-hua,Professor.E-mail:;SHUKe-wei,AssociateProfessor.E-mail:Author introduction：NIUHui-zhu,Ph.Dcandidate.E-mail:Supplementarydataassociatedwiththisarticlecanbefoundintheonlineversion.Homepage:http:/ coal-based carbon materials can not onlymeetthegrowingdemandforsecondarybatteriesbutalsoreduceenvironmentalpollutionandachievethehigh-valueutilizationofcoal.Wangetal.12synthes-izedcoal-basedporouscarbonusingpotassiumper-manganate(KMnO4)as oxidant,sodium hydroxide(NaOH)asanactivatorandsodiumchloride(NaCl)asatemplate.Itexhibitedasodiumstoragecapacityof150.4mAhg1after1000cycles.Similarly,Gaoetal.13preparedcoal-basedcarbonnanofibers(CCNF)throughaspinningmethodusingoxidizedcoal(OC),polyacrylonitrile(PAN)anddimethylformamide(DMF)asrawmaterials.Itdemonstratedacapacityof109mAhg1evencyclingover1000times.Thesefindings collectively affirm the viability of coal-de-rivedcarbonmaterialsinSIBs.Previousstudieshaveproventhattheintroduc-tionofheteroatomscanpromoteelectricalconductiv-ityandgeneratemoreactivesites,therebyimprovingelectrochemical performance1417.Ou et al.18 pre-paredaporousN-dopedcarbonmaterialusingchrys-anthemumascarbonsource,exhibitingaspecificca-pacityof205mAhg1after200cyclesat0.1Ag1.Yanetal.10utilizedphosphorustrichloride(PCl3)asaphosphorussourceandcyclohexane(C6H12)asacar-bonsourcetoobtainanultra-highP-dopedcarbonma-terial(UPC).Itexhibitedhighreversiblecapacityof510.4mAhg1at100mAg1.Thus,improvingtheso-diumstorageperformancethroughheteroatomdopingisparticularlybeneficialforcoal-basedcarbonmateri-als.Long-flamecoal,knownaslow-rankbituminouscoal,istypicallyusedaspowercoalandbringsinevit-able environmental pollution.Utilizing long-flamecoalasacarbonsourceforpreparingcoal-basedcar-bonmaterialscanachieveitshigh-valueutilization.Inthiswork,wepreparedN,Sco-dopedcoal-basedhardcarbon(NSPC1200)withextendedinterlayerspacingbyacombinationoftwo-stepcarbonizationandhet-eroatomdoping.TheNSPC1200exhibitedoutstand-ingelectrochemicalperformanceowingtothecom-binedeffectofexpandedinterlayerspacinganddop-ing.It achieved a sodium storage capacity of314.2mAhg1at20mAg1.Evenafter200cyclesat100 mA g1,it still maintained a capacity of224.4mAhg1.2Experimental 2.1 Material preparationLong-flame coal(Huangyuchuan Coal Mine inOrdos)servedastherawmaterial(TableS1).Hydro-chloricacid(HCl)(coal:HCl=110)andhydrofluor-icacid(HF)(coal:HF=15)wereusedtotreatthelong-flamecoalat60Cfor3htocleanupimpurit-ies.Afterwashinganddrying,apurifiedcoalprecurs-orwasobtainedandnamedasCY.NSPC1200 was prepared through heteroatomdopingbytwo-stepcarbonizationofCYat700Cinargonatmosphere.First,theCYpowderwascarbon-izedinatubefurnaceat1200Cfor2htoobtainPC1200.Subsequently,PC1200,thiourea and NaClweremixedwitharatioof1510intubefurnacefortwo-stepcarbonizationat700Cfor2hataheat-ingrateof3Cmin1.ThetargetsampleNSPC1200wasobtainedafterwashinganddrying.2.2 CharacterizationsTransmission electron microscopy(TEM,FEITecnai G2 F20)and scanning electron microscopy(SEM,FEIVerios460)wereusedtoexaminethemi-crostructure of PC1200 and NSPC1200.The X-raydiffractometer(XRD,Bruker D8 Advance)and Ra-manspectroscopy(THEMDXRxi)wereemployedtocharacterizethecrystallinityandgraphitizationofcar-bonmaterials.Theelementalcompositionandbond-ingstateweredetectedbyX-rayphotoelectronspec-troscopy(XPS,AXISSUPRA).N2adsorption/desorp-tiontestswereconductedusingafullyautomatedsur-faceareaandporesizeanalyzer(BET,MicromeriticsASAP2460)underliquidnitrogenconditions.2.3 Electrochemical measurementThe coal-based carbon materials,super carbonblackandPVDFwerehomogeneouslymixedinNMPwithamassratioof811.Afterdrying,thework-ingelectrode was obtained.The batteries were as-sembledwithsodiumsheetsarethecounterelectrodeand glass fiber separators.The electrolyte was298新型炭材料（中英文）第39卷1molL1NaClO4inamixtureofdimethylcarbonate(DMC)andethylenecarbonate(EC)(11;v/v).Andthe charging/discharging curves were performed onbatterytesting system(CT-4000).Cyclic voltam-metry(CV)measurements were taken on electro-chemicalworkstationwithscanningrateof0.1mVs1,andelectrochemicalimpedancespectro-scopy(EIS)was tested by sweeping the frequencyfrom100000to0.01Hz.3Resultsanddiscussion 3.1 Material synthesis and characterizationFig.1a illustrates the synthesis process ofPC1200andNSPC1200.UsingCYastherawmateri-al,N and S co-doped coal-based carbon materialswerefinallyobtainedthroughatwo-stepcarboniza-tionand heteroatom doping process.The SEM im-agesrevealthatPC1200hasablockyandrelativelyflatsurface(Fig.1b,c),whileNSPC1200hasalooseandporoussurface,presentingahoneycombstructure(Fig.1e,f).Thisstructurefacilitatesrapidelectrolyteinfiltrationintotheelectrode,therebyimprovingthetransportanddiffusionofNa+.ThemicrostructuresofPC1200 and NSPC1200 are further observed byHRTEM.PC1200exhibitsseveralnanostructures,in-dicatingdifferentinterlayerspacings;whileNSPC1200 shows homogeneous interlayer spacingandmorepseudo-graphiticphases(Fig.1d,g).Thesepseudo-graphiticphaseshavealargerinterlayerspa-cing(0.360.40nm),beneficialfortheintercalationandde-intercalationofsodiumions19.TheSEMandTEMtestssuggestthatthetwo-stepcarbonizationandheteroatom doping process can improve the carbonmicrocrystallinestateofNSPC1200,leadingtoexpan-20 mPC12005 mNSPC12002 m(b)10 mPC1200(c)(f)(a)(e)(d)10 nm(g)10 nmPC1200NSPC1200NSPC1200Pure coal carbonized at 1200 oCNaClThioureaN,S-doped carbon materialsCarbonized at700 oCWashingPrecursorNaClCNSNaFig.1(a)SyntheticschematicdiagramofPC1200andNSPC1200.(b,c)SEMimagesofPC1200.(e,f)SEMimagesofNSPC1200.(d,g)HRTEMandSAEDimagesofPC1200andNSPC1200第2期NIUHui-zhuetal:N,Sco-dopedcoal-basedhardcarbonpreparedbytwo-stepcarbonizationand299dedcarboninterlayerspacing.TheXRDandRamananalysesaretestedtogainmoredetailedinformationaboutthemicrostructureofPC1200 and NSPC1200.The XRD results reveal 2diffractionpeaksat24and43forbothPC1200andNSPC1200,corresponding to the(002)and(100)crystal planes(Fig.2a)2021.Compared to graphite(0.336 nm),PC1200(0.367 nm)and NSPC1200(0.383nm)havelargerinterlayerspacing22.Thiscanbeattributedtotheenhancedcarbonmicrocrystallineconfigurationandexpandedinterlayerspacingachievedthroughthetwo-stepcarbonizationprocess,whichfacilitatesreversibleintercalationandde-inter-calationofNa+23.TheRamanspectraexhibit2peaksat1350and1580cm1,correspondingtotheDandGbands(Fig.2b)21,24.TheratioofID/IGcanmeasurethedisorderofhardcarbon2526.AndthecalculatedID/IGvaluesforPC1200andNSPC1200are0.94and1.06,respectively.After doping,the value of ID/IG in-creased,indicating that the introduction of het-eroatomscanincreasetheexternaldefectsites.Lat-ticedefectsareimportantparametersinfluencingelec-trochemicalperformance,andthepresenceofdefectsis generally more conducive to the adsorption ofNa+2729.Furthermore,the effect of carbonizationtemperaturesonthemicrostructureofhardcarbonwastestedthroughXRDandRamanofPC700(Fig.S1a,b).ThecalculatedinterlayerspacingandID/IGvaluesofPC700are0.372and0.953nm,respectively.Thisin-dicatesthatthemanipulationofcarbonizationtemper-aturecanalterthemicrostructureanddefectcomposi-tion,potentially influencing the storage behavior ofNa+.TheN2adsorption/desorptionisothermsareusedto measure the porosity structure of PC1200 andNSPC1200(Fig.2c,d).BothPC1200andNSPC1200exhibit rapid absorption in the low-pressure regionanddisplaysignificanthysteresisat0.51,indicatingtheexistenceofabundantpores.Furthermore,thespe-cific surface areas of PC1200 and NSPC1200 are1020304050607080(100)(002)(a)(b)(c)(d)Intensity/(a.u.)2/()PC1200 NSPC120060090012001500180021002400ID/IG=0.94ID/IG=1.06GDIntensity/(a.u.)Wavenumber/cm1 PC1200 NSPC120000.20.40.60.81.0051015202530Volume adsorbed(cm3 g1,STP)Relative pressure/(p/p0)PC1200 NSPC120005010015020025000.00050.00100.00150.00200.0025 PC1200 NSPC1200dV/dD(cm3 g1 nm1)Pore diameter/nmFig.2(a)XRDpatterns,(b)Ramanspectra,(c)N2adsorption/desorptionisothermcurvesand(d)thecorrespondingpore-sizedistributionsofPC1200andNSPC1200300新型炭材料（中英文）第39卷measuredtobe8.5379and16.5738m2g1,suggest-ing that the addition of NaCl as a template createdmoreporestructures.Thishypothesisisfurthercon-firmedbytheporesizedistribution.ComparedwithPC1200,NSPC1200exhibitsasignificantincreaseinthe number of micropores.This hierarchical porousstructureisbeneficialforthestorageofNa+.Micro-poresprovidesodiumionintercalationtransportchan-nels and decrease contact area between pores andelectrolyte,whilemacroporesreducetheirreversibleelectrodeexpansion30.Theelementalcompositionandbondingconfig-uration of PC1200 and NSPC1200 were analyzedthroughXPStests.AsshowninFig.S2a,PC1200hasC,NandOcontentsof84.35%,1.07%and14.58%,respectively.Afterthedopingtreatment,NSPC1200exhibitedC,N,OandScontentsof88.35%,3.25%,7.80%and0.60%.TheincreasedcontentofNandSelementsindicatesthesuccessfulheteroatomdoping,while the reduction in oxygen content suggests theformationofstablecarbonskeletonandanenhance-ment in the pore structure composition31.Fig.3ashowstheXPSfullspectrumofNSPC1200,corres-pondingto4energylevels:C1s,N1s,O1sandS2p,respectively32.Incontrast,thePC1200onlyexhibitsC1sandO1speaks(Fig.S2b-d).TheC1sspectraofNSPC1200 can be divided into 4 peaks at 284.6(CC),285.1(CN),286.6(CS)and289.4eV(CO)(Fig.3b)3334.The CC bond is the mainformofcoal-basedcarbonmaterials,whiletheappear-anceofCNandCSbondsindicatestheintroduc-tionofNandSelements.Fig.3cillustratestheN1sspectrum of NSPC1200,exhibiting 2 peaks at397.3 eV(pyridinic-N)and 399.1 eV(pyrrolic-N).Thesenitrogenconfigurationsenhancetheadsorptionofforeignatoms,increasingtheactivesitesforsodi-umstorage.Thepresenceofpyridinicnitrogengener-atesmoreexternaldefects,therebyboostingthespe-cificcapacityandimprovingtheelectrochemicalper-formance.Additionally,pyrrolicnitrogencanacceler-atethetransferofelectrons,thusenhancingthesur-facecapacitanceprocess35.Fig.3dillustratestheS2p8006004002000Intensity/(a.u.)Binding energy/eVO 1sC 1sN 1sS 2p296294292290288286284282Intensity/(a.u.)Binding energy/eVCNCCCSCOC 1s404402400398396394Intensity/(a.u.)Binding energy/eVpyrrolic-Npyridinic-NN 1s172170168166164162160C-SOX-CIntensity/(a.u.)Binding energy/eVS 2pS 2p1/2S 2p3/2(a)(b)(c)(d)Fig.3(a)XPSsurveyspectraofNSPC1200.(b,c,d)Thehigh-resolutionC1s,N1sandS2pspectraofNSPC1200第2期NIUHui-zhuetal:N,Sco-dopedcoal-basedhardcarbonpreparedbytwo-stepcarbonizationand301spectrum of NSPC1200,showing 3 peaks at 163.1,164.4and168.0eV.Theformer2peaksareattrib-utedtotheCSxC(x=12)covalentbondofthiophene-S,while the last peak corresponds to theCSOxC(x=24)group36.TheintroducedShet-eroatomsnotonlyparticipateintheFaradaicreactionwith Na+,but also generate additional active sites,therebyimproving reversible sodium storage reac-tions.And the formation of CSOxCalso im-provesthewettabilityofelectrolyte,achievingafasterkineticprocess37.TheXPStestsconfirmthesuccess-fuldopingofNandSelementsintocarbonskeleton.3.2 Electrochemical performanceThe charge/discharge curves of PC1200 andNSPC1200at20mAg1areshowninFig.4a,b.Allhardcarbonexhibitsimilarcharge/dischargecurves,whicharecharacteristicofsodiumstorageincarbonmaterials3840.The curve can be divided into 2 re-gions:slope(0.1V)andplateau(0.1V),corres-pondingtoadsorbedandintercalatedsodiumstorage,respectively41.The NSPC1200 exhibits a highinitialdischargespecificcapacityof314.2mAhg1at20mAg1withICE=50.82%.Thissignificantlysur-passes the sodium storage capacity and ICE ofPC1200(198.34mAhg1withICE=43.54%).Thedifferencecanbeattributedtothehigheroxygencon-tent in PC1200(14.58%)compared to NSPC1200(7.8%),which induces numerous irreversible reac-tions and forms a thicker solid electrolyte inter