同步輻射X-射線和中子衍射在儲(chǔ)能材料研究中應(yīng)用

ApplicationsofsynchrotronX-raysandneutronsdiffractioninenergystoragematerialsresearch【摘要】Abstract：SynchrotronX-rayandneutrondiffractionfacilitiesareverypopularandindispensablescientificresourcesthatprovidepowerful instruments and experimental techniques for bothfundamentalandappliedresearchesaroundtheworld.X-raysandneutronsinteractwithmatterindifferentandalsocomplementaryways,andrecentlyhavebeenextensivelyusedforstudyingenergystoragematerialsattheelectronic,atomicandmolecularlevels,andevenextendedtoengineeringscale.Inthisarticle,wewillbrieflyintroducesynchrotron X-ray and neutron scattering techniques and theirdifference,similarityandcomplementarity.Advantagesofsynchrotronhigh-energyX-rayswillalsobepresented.Theuniqueandpowerfulcapacityofneutronscatteringforhydrogenstoragematerialstudywillbeshown.Wealsopresentsomeexamplesofin-situ/operandostudyofthe atomic structure evolution of Na1–δNi1/3Fe1/3Mn1/3O2andLiNi0.5Mn1.5O4active electrode materials during synthesis andelectrochemicalintercalationforsodiumionbatteryandlithiumionbattery.Finally,thefutureperspectivesofsynchrotronX-rayandneutrondiffractiontechniquesinthefieldofmaterialsscienceforenergystoragetechnologywillbediscussed.【期刊名稱】?jī)?chǔ)能科學(xué)與技術(shù)【年(卷),期】2017(006)005【總頁數(shù)】9【關(guān)鍵詞】Keywords：synchrotron;X-ray;neutrondiffraction;energystoragetechnology;electrodematerialTheenergyconservationlawtellsusthatwecannotcreateoreliminateenergy,wejuststoreandconvertenergyfromonetypetoanotherforourdailyactivities.Obviously,highefficientandenvironmentallybenignenergyconversionandstoragetechnologiesarehighlydesiredandarethefocusofgrowingresearchanddevelopmenteffortsworldwide.However,physics principles often set up high barriers betweenperformanceandsafety,andmanycompetingfactorsbetweenstabilityandactivity,capacityandcyclability,etc.inactiveenergymaterials.Basicknowledgeatelectronic,atomicandmolecularlevelsiscriticalnotonlyforbetterunderstandingbutalsoforfuturedevelopmentofadvancedenergymaterials.SynchrotronX-rayandneutrontechniquesplayaveryimportantroleandhavebroadapplicationsinenergystoragematerialsresearch.SincethediscoveryofX-raysbyW.C.ROENTGENinlate1895,andneutronbyJ.CHADWICKin1932,X-raysandneutronshavebeenwidelyusedinvariousfields.Especially,theacceleratorbasedsynchrotronX-rayandspallationneutronsourceshavesignificantlyadvancedtheirinstrumentationaldevelopmentandapplicationsforresearchinalmostallscientificandengineeringdisciplines.X-raysareelectromagneticwavesandalsocalledphotons,whileneutronsaresubatomicparticles.BothX-rayandneutroncarrynochargeandhavespin.Table1listssomepropertyandcharacteristicsofX-raysandneutronsforreference.Generallyspeaking,X-raysinteract with electrons of atoms via electromagneticinteraction,whileneutronsinteractwithatomicnucleiviaveryshort-rangestrongnuclearforces,andalsointeractwithunpairedelectronicspinsviathemagneticdipoleinteraction[1-5].Neutronsareimportantforstudyingmagneticmaterials,whileX-rayscanalsoprobespinsviaveryweakrelativisticeffects.SynchrotronX-raytechniquescanbegenerallycategorizedintodiffraction/scattering,spectroscopyandimaging/tomography,whichcanbecombined,time-resolved,polarizationdependent,coherencerelated,furtherdetailed.Herewewillbemainlyfocusedontheelasticdiffractionpartforatomicstructure characterization, although the particular application neutron scattering in storage materials will brieflydiscussedlater.Brief introduction to synchrotron X-ray and neutrondiffractionInpractice,oneofthemostimportantparametersinX-rayandneutrondiffractionistheso-calledscatteringcrosssection,,wherebisthescatteringlength,whichmeasurethescatteringpowerofX-raysandneutronsbyanatom.Fig.1showstheX-rayandthermalneutronscatteringlengthofsomeselectedelements.OnecanseethattheX-rayscatteringlengthisproportionaltotheatomicnumber,becauseX-raysareinteractingwithelectronsofatoms.X-rayscatteringlengthatphotonenergyof10keVand100keVisalsoplottedforcomparison,whichindicatesthatwithincreasingphotonenergytheX-rayscatteringlengthisreduced.ThisfactorshouldbeconsideredwhenusingsynchrotronX-rays.InFig.1,italsocanbeseenthattheneutronscatteringlengthofthesampleelementwithdifferentisotopescanbedrasticallydifferent,likethehydrogenanddeuterium,whichevenhaveasigndifference.Suchauniquefeaturemakesisotopesubstitutionmethodveryimportantandusefulinneutronscatteringexperiment.Vanadiumhasanearlyzeroscatteringlength.Thisiswhypeopleoftenusevanadiumforsamplecontainersinmanyneutronscatteringexperiments.ItisknownthatneutronsusuallyhavemuchhigherpenetrationcapacitythanX-rays,thuscanbeusedtoprobebulkysamples,exceptthosecontaininghydrogenorelementswithlargeneutronabsorption.Buttheavailabilityofhigh-brilliancesynchrotronhighenergyX-rayswithtunableenergygeneratedbyhigh-energysynchrotronradiationsourceshassignificantlyadvancedthefieldofmaterialsresearch,especiallyforin-situ,operando,studiesoffunctionmaterials,inbulkformsornanoscalestructures,inrealisticconditionsandinrealtime.Fig.2(a)showsX-rayscatteringcrosssectionofleadasafunctionofphotonenergy.Below1MeV,theX-rayinteractionswithmatterincludethecoherentandincoherentscatteringandthephotoelectroneffect,whilethenuclearinteractionsoccurathigherenergy.Nowadays,X-rayswithphotonenergyofabove~40keVareconsideredashigh-energy(HE)X-rays.Theweakscatteringpowerofhigh-energyX-raysmeansaweakabsorption,leadingtoalargepenetrationpower,asshowninFig.2(b),fromwhichonecanseethatthelabX-rayswithCuKαradiationcanonlypenetrateafewmicronthickion,whilesynchrotronHEX-rayswith115keVcaneasilypenetrateafewmillimeteriron,showingbulksampleproperties.Ontheotherside,theweakscatteringpowerofhigh-energyX-raysrequireshighfluxandsometimesbulkysamples,inordertoperformhighqualityhigh-energyX-rayexperiments.High-energyX-rayshavemanyadvantageslikehighpenetration,lowabsorption,smallscatteringangleandwidereciprocalspacecoverageetc.Suchadvantagesmakehigh-energyX-raysparticularlysuitableforin-situoperandoinvestigationofadvancedmaterialsincomplexsampleenvironments,e.g.inlowandhightemperature,undermagnetic,electricandstressfield,highpressureorwithcombinedexternalstimuli,oreveninchemicallyhazardous,corrosiveandradioactiveconditions[6-10].ApplicationofneutronscatteringforhydrogencontainingmaterialsAtfirst,wewanttoemphasizeaveryimportantanduniquefeatureinneutronscatteringthatisitsabilityofstudyinghydrogencontainingmaterials.Hydrogenisthelightestelement,whichmakesitverydifficultforX-raystoprobehydrogenatomsinmaterials.Unfortunately,itisalsoverydifficultforneutronstoseehydrogen,evenithasareasonableneutronscatteringlength(Fig.1).WehavetopointoutthatFig.1plotsthecoherentscatteringlength.Hydrogenhasahugeincoherentscatteringcrosssection,whichgivesrisetoveryhighincoherentscatteringbackgroundinneutrondiffractionspectraofhydrogen-containingmaterials.Inorderforneutronstoseewherehydrogenatomsarelocatedinacompoundorsystem,onehastoreplacehydrogen(H)byitsisotope,deuterium(D).Neutronscatteringplaysanirreplaceable role and provides fundamental knowledge in thisparticularfield.Hydrogenmoleculeisthesimplestmoleculewithquantumstates,inwhich two protons are indistinguishable fermions, thus has anantisymmetric(AS)wavefunction.Ifthespinsofthetwoprotonsareantiparallel,itiscalledpara-hydrogen.Ifthetwospinsareparallel,itiscalledortho-hydrogen.FromTable1,onecanseethatthepopulationofpara-andothor-hydrogenistemperaturedependent.Theenergytransferfrompara-hydrogentoortho-hydrogeninH2solidis14.7meV,whichisafingerprintspecificallyformoleculehydrogenanditsinteractionwithsurroundings.Wehaveemployedneutronscatteringtechniquestoin-situinvestigatehydrogenstoragecapabilityandmechanismincarbonnanotubesandalso dynamic properties of metal hydrides [11-12]. We used quasielasticneutronscattering(QENS)instrumenttomonitorhydrogenadsorptioninsinglewalledcarbonnanotubebundles.TheQENSinstrumentcanprovideusrichinformationofhydrogendynamicbehavioranditsinteractionwithabsorbents.MolecularhydrogenhasquantumrotationalenergylevelsgivenbyEJ=BJ(J+1),whereJistherotationalquantumnumberandBtherotationalconstant(=7.35meVforsolidhydrogen).Fig.5showsaninelasticneutronspectrumofH2moleculeadsorbedincarbonnanotubes.Theshapepeakat14.5meVcorrespondstothequantumrotationaltransitionfromJ=0(para-)toJ=1(ortho-state)oftheadsorbedhydrogenmolecules,ambiguouslyindicatingthatmoleculehydrogenispresent.Thispeakbecomesweakerandbroaderwithincreasingtemperature,whilethepeakpositionremainsalmostunchanged.Theobservedtransitionenergyof14.5meVisslightlylessthanthe14.7meVfoundinpuresolidhydrogen,implyingthatadsorbedhydrogenmoleculesencounterrelativelylittlehindranceforrotation,probablyduetotheweakVanderWaalsinteractionsbetweenhydrogenandcarbonnanotubes.Thelinearincreaseofthepeakwidthwithtemperatureincreaseindicatesthatthehydrogenmoleculesbecomelessandlessboundtothecarbonnanotubes.InoperandosynchrotronX-raystudyofsodium-ionbatterymaterialsInsitusynchrotronX-raydiffraction(XRD)hasproventobeapowerfultechniquetoprobethesodiuminsertionmechanisminsodiumionbatteries.Wehaveusedinsitu/operandohigh-energyX-raydiffraction(HE-XRD) to understand the phase transformation NaNi1/3Fe1/3Mn1/3O2materialsduringNaionintercalation.Duringtheoperandoexperiments,high-energyX-raysaredirectedtotransmitthrough a perforated 2032-type coin-cell containing our newlysynthesized NaNi1/3Fe1/3Mn1/3O2 materials. The insitu HE-XRDpatternsoftheNaNi1/3Fe1/3Mn1/3O2duringchargeanddischargeareillustratedinFig.4.TheinsituHE-XRDdataclearlyindicatetheexistenceofanonequilibriumsolid-solutionreactionduringchargingwhenthecut-offvoltageofchargewassetto4.0VasevidentinFig.4(a).Duringthedischarge,theXRDpatternindicatesanexactoppositeelectrodeevolutioncomparedwithcharge,suggestingthatthephasetransformationofNa1–δNi1/3Fe1/3Mn1/3O2isreversiblethroughanO3–P3–P3–O3sequenceduringcycling.WealsocangetthechangeinlatticeparametersofNa1–δNi1/3Fe1/3Mn1/3O2duringcycling.Clearly,thestructureofNa1–δNi1/3Fe1/3Mn1/3O2isverystablewhencycledinthevoltagerangeof2—4.0V.Bycontrast,asevidentinFig.4(b),thephasetransformationofNa1–δNi1/3Fe1/3Mn1/3O2iscompletelydifferentwhenthecutoffvoltageissetto4.3V.ThephasechangefollowsthesequenceofO3toP3whenchargedfrom3.2Vto4.0V,butinthechargevoltagerangeof4.0—4.3V,the(003)P3shiftstohigherangleandsplitsintotwoagain.Thesetwopeakseventuallymergetoanew(003)peak,indicatinganewnonequilibriumphase,whichisassignedtoamonoclinicO3′phaseconsistingofadistortedlatticeincomparisontoanidealhexagonalcell.Note that a two-phase reactionwith the coexistence of P3hexagonalandO3′monoclinicphasesoccursinthechargevoltagerangeof4.0—4.1V.InsituXRDshowsareversibleevolutionofO3–P3–O3′duringcharge.Thelatticeparametersincriticalphasechangewerecalculated and are summarized in S2 of the SupportingInformation.ThelatticeparametersforsuchO3′monoclinicphasesarea=8.5394?,b=5.3697?,andc=2.4631?.Interestingly,asingleO3′monoclinicphaseismaintainedtocutoffvoltageof4.3V.Duringdischargefrom3.5to3.0V,the(003)peakshiftstoalowerangle,andtheO3′monoclinicphasetransformstoP3′monoclinicphase.TheO3phaseisrecoveredviaO3′–P3′–O3duringdischarge.ThenatureofthestructuralevolutionofP2-Na0.67[Mn0.5Fe0.5]O2andP2-Na0.67[Mn0.65Ni0.15Fe0.2]O2uponcyclingwerestudiedbyusingcombinedX-rayandneutronpowderdiffraction(XRPDandNPD)[14].Thephasediagramofthetwocompositionsasafunctionofsodiumcontentisdeterminedusingoperandodiffractionexperiments,andthestructureoftheunknownhighvoltagephaseissolvedbyX-raypairdistributionfunction(PDF)analysis.Thegoodfitbetweentheaveragestructure,determinedbydiffraction,andthemeasuredPDFisaconsequenceofthelowoccupanciesandweakscatteringcoefficientofsodiumatoms.Thestructureofthehighvoltagephaseofthenickelsubstitutedoxidewassimilarlydetermined,usingX-rayPDFanalysisonachemicallyoxidized“Z”-Na0.1Fe0.2Mn0.65Ni0.15O2sample(Fig.5).The sodium content reached by chemical oxidation of P2-Na0.67Fe0.2Mn0.65Ni0.15O2isslightlylowerthanwhatisachievedelectrochemically.Complementaryneutronandsynchrotronstudyofhigh-voltagespinelcathodeforlithium-ionbatteriesResearcheffortsareinprogressworld-widetodevelopreliable,high-performancecathodematerialsforadvancedlithium-ionbatteries,pavingthewaytoasecureandsustainableenergyfuture.Amongthecathodematerials,LiCoO2andLiTMO2(TMisamixtureoftransitionmetalelementsand/orAl),LiMn2O4andLiFePO4arethemostwidelyusedmaterialsandstandsforthreedifferenttypesofstructures,suchaslayered-,spinel-andolivine-structure,respectively.Toimprovetheenergyandpowerdensity,onewantstoincreasethecapacityand/ortheoperatingvoltage.LiNi0.5Mn1.5O4isatypeofspinelmaterialwithdischargevoltageplateauaround4.7V,whichisamongthehighestones.Amongtheclaimedhighvoltagematerials,LiNi0.5Mn1.5O4isthefew demonstratinggood cycleandcalendar life, beinga goodcandidatefor5Vlithiumionbatteries.However,thematerialproducesbydifferentsynthesismethodsdemonstratedifferentelectrochemicalproperties.Itisknownthat,dependingonthesyntheticroutes,LiNi0.5Mn1.5O4hasastructureofface-centeredspinel(Fd3m)orprimitivecubiccrystal(P4332),whereface-centeredspinel(Fd3m)performancebetterthanprimitive(P4332)[15].Eventhematerialproduced from the same synthetic route, the variation on thecalcinationprocess(temperatureandheatorcoolingrate)willalsoresultindifferencesinperformance.AsweknowthatX-raycanhardlydistinguishNiandMn,thuswillgivealmostidenticaldiffractionpatternsforthetwostructures.Tounderstandthedifferencesinproperty,weneedtohavesufficientinformationonthematerialstructurechangeatdifferentcalcinationconditionorduringthecalcinationtemperaturechangebyemployingbothneutronandhigh-energyX-raydiffractiontechniques.Aswementionedpreviously,synchrotronhigh-energyX-raysareverysuitedforin-situprobingmaterialsformationandtransformationofbulkysamples.Itisastraightforwardexperimenttomonitormaterialsynthesisprocessduringhightemperaturecalcination.Fig.6isaphotooftheexperimentalsetupforin-situhigh-energyX-raydiffractionduringsolidstatematerialsynthesisathightemperatureatBeamline11-ID-C, Advanced Photon Source (APS) at Argonne NationalLaboratory.AcommercialfurnacewasusedandHEX-rayspenetratethrougha2mmthickpelletofamixtureofNi0.25Mn0.75CO3precursorandLi2CO3inamolarratioof4∶1.Thesamplewasheatedupto800℃ataheatingrateof1℃·min-1,thewavelengthofX-rayusedwas0.1078?.A2DX-raydetectorwasusedtocollecttheX-raydiffraction(XRD)patternswithaspeedofonespectrumperminute.Fig.7(a)showsacontourplotofinsituHEXRDpatternsillustratingthestructuralevolutionofthematerialduringtheheatingprocessfromtheroomtemperatureto800℃,whichclearlyshowsthatamajorreactionoccurredatabout500℃.Thediffractionpeaksfromthestartingmaterialcompletelydisappearedandasetofnewpeaksofthefinalproductemerged.Fig.7(b)depictsthe1DcovarianceanalysisofadjunctHEXRDpatternsinrealtimespace,Threedownwardpeaksatabout290℃,390℃,and540℃suggestthatthreedifferentreactionsoccuratthespecifictemperatures.FromtheHE-XRDdata,thereseemstobenostructuralchangeabove540℃.However,itisknowthattheformationoftheorderedanddisorderedspinelstructuresisstronglydependentonthehightemperaturesynthesisprocedure.Inordertoinvestigatehightemperaturestructurechangesandpossiblemigrationmechanismoftransitionmetalions,wehavecarriedoutin-situneutrondiffractionmeasurementsofthesamemixtureforLiNi0.5Mn1.5O4atvarioushightemperaturesattheneutroninstrumentVULCANattheSNSofORNL.BecauseneutrondiffractiondatacollectiontimeismuchlongerthanHE-XRDmeasurements,thefurnacehadtobeheldatspecifictemperaturesfor3htocollectacompleteneutrondiffractionpattern.Fig.8showsthein-situneutrondiffractionpatternsat600,700,800and900℃.FromFig.8,onecanseethatthediffractionpatternsat600℃canbedescribedbythedisorderedspinelstructurewithspacegroupofFd-3m,inagreementwiththeHE-XRDdata.However,at700℃,asetofnewpeaks,labeledbyarrows,wereobserved,andthesepeaksdisappearedagainwhenthetemperaturewasincreasedto800℃andabove.Rietveldrefinementanalysisindicatedthattheextrapeakat700℃belongedtotheorderedLiNi0.5Mn1.5O4spinel(withspacegroupP4332).Inthedisorderedspinel,NiionsandMnionsrandomlyoccupied50%ofoctahedralsitesintheFCCoxygenframeworkwithoutformingalongtermorderingbetweenNiandMn.Ontheotherhand,intheorderedspinel,oneNiionpairswiththreeMnionstoformastablerepeatingunitintheFCCoxygenframework,resultinginextrapeaksintheneutrondiffractionpattern.Thisimpliesthattheorderedspinelisenergeticallymorestablethanthedisorderedspinel.Thephasetransitionfromtheorderedspineltothedisorderedspinelathightemperaturesabove700℃wasprimarilydrivenbytheentropy,whichtendstomaximizetherandomnessofthesystem.Thedisorderedspinelat600℃andbelowmightbeduetotherandomdistributionofNiandMnintheNi0.25Mn0.75CO3precursor.Rightaftertheformationofthespinel,themobilityoftransitionmetalionsisverylow.Themigrationoftransitionmetalionswasonlyenabledatatemperaturearound700℃toallowforthetransitionofthemetastabledisorderedspinelintoastableorderedspinelatabout700℃.5SummaryAdvancedfunctionalmaterialsarethepivotsforthedevelopmentandcommercializationofenergystoragetechnologiesformodernsociety,whichbecomeincreasingsophisticatedinordertofinetunemanycompeting interactionsandalsotooptimize multiplecontrollingparameters.Fundamentalknowledgeatvariouslevelsisalwaysthekeydriverforrationalmaterialdesignanddiscovery.SynchrotronX-rayandneutronscientificuserfacilitieshavebeenextensivelyemployedtotacklematerialissuesin almostevery scientific andengineeringdisciplines,andhavegreatlyadvancedourknowledgeofenergystoragematerialsatelectronic,atomicandmoleculelevels.Particularly,recentandfutureimprovementsinsynchrotronandneutronsourcesandinstrumentationhaveprovideduswithalargesetofstateofthearttechniquesforin-situ,operando,studiesofenergystoragematerialsinrealisticconditionsandinrealtime,withincreasingtemporalandspatialresolution.Withthehelpofsynchrotronandneutronfacilities,wehavegainedmuchdeeperinsightsintheenergystoragematerialsandhavewitnessedflourishingactivitieswithinnumerablebreakthroughsanddiscoveriesforfutureenergystoragetechnologydevelopments.AcknowledgmentArgonneNationalLaboratoryisoperatedfortheU.S.DepartmentofEnergybyUChicagoArgonne,LLC,underContractNo.DE-AC02-06CH11357.ThisresearchusedresourcesoftheAdvancedPhotonSource,U.S.DepartmentofEnergy(DOE)OfficeofScienceUserFacilitiesoperatedfortheDOEOfficeofSciencebyArgonneNationalLaboratoryunderContractNo.DE-AC02-06CH11357.Wewouldlikethankallourcollaboratorsandusersfortheirexcellentworkusinghigh-energyx-raysattheBeamline11-ID-C,AdvancedPhotonSource.WeareverygratefultoCharlesKurtz,GuyJenningsandRichardSpencefortheirtechnicalsupports.References：HUBBELLJH.Photonmassattenuationandenergy-absorptioncoefficientsfrom1keVto20MeV[J].Int.J.Appl.Radiat.Isot,1882,33:1269-1290.ATTIXFH.Introductiontoradiologicalphysicsandradiationdosimetry[M].NewYork:Wiley-VCH,1991.HUBBELLJH,VEIGELEWJ,BRIGGSEA,etal.Atomicformfactors,incoherentscatteringfunction,andphotonscatteringcrosssections[J].J.Phys.Chem.Ref.Data,1975,4:471-538.LOVESEYSW.Theoryofneutronscatteringfromcondensedmatter[M].Oxford:ClarendonPress,1984.BeeM.Quasielasticneutronscattering,principlesandap