1Lithium-ionbatteries(LIBs)arecommonineverydaylifeandthedemandfortheir2rawmaterialsisincreasing.Additionally,spentLIBsshouldberecycledforachieving3acirculareconomyandsupplyresourcesfornewLIBsorotherproducts.Especially4therecyclingoftheactivematerialoftheelectrodesisinthefocusofcurrentresearch.5Existingapproachesfortherecycling(e.g.,pyro-,hydrometallurgyorﬂotation)still6havetheirdrawbacks,suchasthelossofmaterial,generationofwaste,orlackof7selectivity.Inthisstudy,wetestthebehaviorofcommerciallyavailableLiFePO48andtwotypesofgraphitemicroparticlesinadielectrophoretichigh-throughputﬁlter.9Dielectrophoresisisavolumedependentelectrokineticforcethatiscommonlyusedin101 microﬂuidicsbutrecentlyalsoforapplicationsthatfocusonenhancedthroughput.In11ourstudy,graphiteparticlesshowsigniﬁcantlyhighertrappingthanLiFePO4particles.12TheresultsindicatethatnearlypurefractionsofLiFePO4canbeobtainedwiththis13techniquefromamixturewithgraphite.141Introduction15Lithium-ionbatteries(LIBs)powerelectricaldevicesinnearlyallpartsofmodernsociety.16Forexample,LIBsareusedinportableelectronicsandelectricvehicles.Consequently,the17demandforLIBresourcesgrows.1TorecovermaterialsofspentLIBs,therecyclingofelec-18trodesisafocusofcurrentresearch.AsaboutonehalfoftheweightofLIBsconsistsof19theactivematerialofanodeandcathode,theirrecyclingisdesirable.2Cathodeactivema-20terialstypicallyarelithiummetaloxides(e.g.,LiCoO2,LiFePO4orLiNi1/3Mn1/3Co1/3O2),21whereasgraphiteiscommonforanodes.1,2Anodeandcathodeconsist,amongcarbonblack22asconductiveadditiveandapolymerbinder,ofacurrentcollector(CuorAlfoil)towhich23theactivematerialadheres.2–4Currentcollectorandactivematerialcanbeseparatedby24both,chemicalandmechanicalapproaches,suchascrushingandsieving.1,3–5Typically,one25productoftheseprocessesistheso-calledblackmass,amixturefromanodeandcathode26activematerial.4Currentrecyclingtechniquesforblackmassare,forexample,pyro-orhy-27drometallurgicalandfocusontherecoveryofcathodeactivematerialbecauseofitshigher28valuecomparedtographite.Graphitemightbelostorburnedasenergysourcewithinthe29recyclingprocess.1,2,5–7Yetprocessesexistwheregraphitecanberecovered.Inhydrometal-30lurgicalapproaches,thelithiummetaloxidesaredissolvedinacidduringaleachingstepand31recoveredinsubsequentunitoperations.Graphitecansimplyberecoveredbyﬁltrationafter32theleachingstep.4Butassigniﬁcantamountsofliquidwastesareproducedinthisrecycling33pathway8itwouldbeneﬁtfromaneﬃcientsortingstepbeforetheleachingtoreducethe34amountofchemicalsneeded.Astheactivematerialsareessentiallymicroparticles,9–11di-35rectrecyclingusingparticleseparationtechniquescouldplayavitalrolewithintherecycling362 processtoenhanceorreplaceexistingrecyclingapproachesofLIBs.Oneapproachwhichis37wellestablishedforparticulatesystemsandcapableofhandlinglargeamountsofproduct38isﬂotation,whichwasalsoappliedtoseparateblackmass.Thisworksbecauseanodeand39cathodematerialshowdiﬀerentwettability.5,7,12–14However,accordingtoNeumannetal.,440theprocessneedstobeoptimizedfurtherastheachievablerecoveryratesarecurrentlytoo41low.Otherdirectapproachesthatutilize,forexample,eutecticsaltsorionicliquidscanbe42foundintworecentreviews15,16thatelaboratethesetechniquesinmoredetailthanitisthe43scopeofthisstudy.44Thispaperinvestigatesthepossibilitytoaddressparticlesfoundwithinblackmassusing45dielectrophoresis(DEP)athighthroughput.DEPisthemovementofapolarizableparticle46inaninhomogeneouselectricﬁeld.Usually,itisusedinthebiomedicalﬁeldandprimarilyin47microﬂuidicdevices.17,18AlthoughDEPislabel-free,hashighselectivity,andthecapability48ofaddressingnano-tomicrometer-scaledparticles,19–21fewstudiesaddressedrecyclingorthe49throughputthatwouldberequiredforthis.22–27WhileDEPiswellstudiedwithbiological50samples,suchasDNA28,29andcells,30–33theseparationofnon-biologicalparticles,aside51frompolystyreneparticles,israrelydescribedinliterature.18Thisstudyisdesignedto52expandthisﬁeldbyusingartiﬁcialblackmasstoshowthatconductiveparticlescanbe53addressedwithanelectrode-basedDEPseparatorathighthroughput.Byusingasetup54basedonprintedcircuitboards(PCBs),weassessthebehaviorofLiFePO4andgraphite55microparticlesandtheirmixtureundertheinﬂuenceofDEP.Tothebestoftheauthors’56knowledgetheseparationofLIBelectrodematerialusingdielectrophoresishasnotyetbeen57addressed.Thisstudyaimstoserveasastartingpointforfutureresearchinthisﬁeld58bydescribingthepossibilitiesandlimitationsofDEPasaseparationtechniqueforthese59materials.60 3 Figure1:Renderedoverviewoftheseparator.Thesuspensionispumpedfrominlettooutletthroughachannelformedbytwoprintedcircuitboards(PCBs),asilicongasketandthepolypropylene(PP)holders.ThePCBsfeatureaninterdigitatedelectrodestructure(bottomrightinsert)thatareusedtogenerateahighlyinhomogeneouselectricﬁeld.2MaterialsandMethods612.1Dielectrophoreticseparator62Theseparatorusedinthisstudyisanupdatedversionoftheonewhichwasevaluatedand63publishedinRef.25andisdesignedtoselectivelytrapparticleswhenanelectricﬁeldis64applied.AnoverviewofthedevicecanbeseeninFigure1.Thekeyfeatureofthisdevice65aretwoinexpensive(<1e/pc.)customdesignedPCBs(manufacturedbyJiaLiChuang66(HongKong)Co.,Limited,China)withasizeof45×150mm,whichisslightlydiﬀerent67fromthepreviousdesign.25Theimproveddesignshowedsimilarperformancewithreduced68PCBsizeandenergydemand.Thenewdesignhasanimpedanceof20Ωat500kHz69incomparisonto13Ωfromtheolddesign.ThePCBsarecoveredbyaninterdigitated70electrodearraywithanelectrodewidthandspacingbothbeing250µm.ThetwoPCBs71faceeachotherandareseparatedbya0.5mmsiliconegasket.ThetwoPCBstogether724 withthegasketformachannel.Thegasketismanuallycuttoformachannelthatis73about175mm×38mm×0.5mm(L×W×H)andthushasatheoreticalvolumeof3.3374mL.Weadditionallymeasuredthevolumeusingascaleandfoundthattheactualvolumeis752.8mL±0.1mL,whichisslightlylowerandlikelycausedbyacompressionofthesealing.The76calculatedheightofthesealingresultstobe0.42mm.Thisgivesaaverageresidencetime77of28sat6mL/minand17sat10mL/mininthechannel.Consequently,at6mL/min,78anaveragevelocityof6.3mm/scanbeexpectedandof10.4mm/sat10mL/min.The79electrodesareconnectedtoapowerampliﬁer(F30PV,PendulumInstruments,Sweden)80whichiscapableofprovidingupto75Vppatmaximumcurrentof2A.Thesinusoidal81signalwasgeneratedbyasignalgenerator(RigolDG4062,RigolTechnologiesEUGmbH,82Germany),monitoredusinganoscilloscope(RigolDS2072A,RigolTechnologiesEUGmbH,83Germany)andpoweranalyzer(PPA1510,Newtons4thLtd,Leicester,UnitedKingdom).84Thesuspensionwaspumpedusingapistonpump(IsmatecMCP-CPFIP65withpump85headFMI202QP.Q0.SSY,Cole-ParmerGmbH,Germany).86Theoperatingprincipleisdescribedindetailelsewhere.25Brieﬂy,DEPcanbeanat-87tractiveforce(positiveDEP/pDEP)ifaparticleisbetterpolarizablethanthesurrounding88mediumorarepulsiveforce(negativeDEP/nDEP)whentheparticleislesspolarizable.Pos-89itiveDEPguidesparticletowardslocalﬁeldmaxima,whereasnDEPpushesparticlesaway90fromthem.17Thiscanleadtoaseparationaswaspreviouslyshownseveraltimes.25,34,3591WhetheraparticleexperiencespDEPornDEPdependsonthereal-partoftheClausius-92Mossottifactor(CM),whichisdeﬁnedas1793Re(CM)=Re󰀣˜εp−˜εm˜εp+2˜εm󰀤,(1)withthecomplexpermittivity˜ε=ε0εr−iσω.Thecomplexpermittivityincorporatesnotonly94thepermittivityεbutalsotheangularfrequencyoftheelectricﬁeldωandtheconductivity95ofamaterialσ.Re(CM)isboundbetween−0.5and1.0andisnegativeincaseofnDEP965 andpositiveincaseofpDEP.Finally,theDEPforceFDEPforasphericalandhomogeneous97particlecanbeapproximatedas98FDEP=2πr3pεmRe(CM)∇|Erms|2(2)withrp,theradiusoftheparticle,theelectricﬁeld,Erms,andthepermittivityofthesur-99roundingmedium,εm.Conductiveparticlesinamediumwithlowconductivity,asused100inthisstudy,willusuallyexperiencepDEP.FDEPisnotonlydependingontheparticle101andmediumpolarizabilitybutalsoontheparticlevolume(r3p)whichisimportantinthe102following.1032.2Particles104 Figure2:SEMimagesofLiFePO4(A&D),KS6syntheticgraphite(B&E)andC-NERGYActilionGHDR15-4(C&F)microparticles.Thescalebarinthetoprowequals1µmand300nminthebottomrow.Pleasenotethatthemagniﬁcationandconsequentlythescalebarvariesinsize.Theparticlesinvestigatedhereallarecommerciallyavailableandarespeciﬁcallydesigned105forbatteryresearch.WechoseLiFePO4(NanograﬁNanoTeknolojiAS,Turkey)asacathode1066 material,notonlybecauseitiswidelyusedforLIBsbutalsobecauseitisconsideredto107havelowtoxicity,whichmakesitmoreconvenienttoworkwith.11,36,37LiFePO4ascathode108materialiscarboncoatedtoenhanceitsotherwisepoorconductivity(about10nS/cm−1).38,39109Thisleads,accordingtothedistributor,toanelectricalconductivityof0.88S/m.Theused110LiFePO4showsadistributedparticlesizefromseveralhundrednmtoafewµm(Table1,111Figure2A&D).ThesmallsizeoftheLiFePO4particlesanditshighspeciﬁcsurfacearea112isaresultfromdesignoptimizationasthisisfavorablefortheperformanceofbatteries.40113ThisisintherangeofsizesmentionedintheliteratureforapplicationonLIB41–44andalso114intherangeofthesizereportedforsomeothercathodematerials.45Additionally,twotypes115ofgraphiteparticleswhereselected.TimrexKS6(MSESuppliesLLC,USA)isasynthetic116graphitewithhighpuritywhichcanbeusedasconductiveadditiveforanodesandcathodes.117Accordingtothemanufacturer(ImerysGraphite&Carbon,Switzerland),itislargerthan118theLiFePO4particles(Table1,Figure2B&E).ThesecondtypeofgraphiteC-NERGY119ActilionGHDR15-4(providedbyImerysGraphite&Carbon,Switzerland),herereferredto120asActilion,isanactivematerialforanodesofLIBsandsigniﬁcantlylargerthantheother121twomaterials(Table1,Figure2C&F).Thelargersizeofgraphitethatisusedasactive122materialinanodesinLIBswasalsodescribedintheliterature10,11,44andagainisaresults123fromoptimizingthebatteryperformance46.BothgraphiteandLFParehighlyconductive124comparedtothesuspensionandthuswillshowpDEPatallfrequenciesusedinthisstudy125(seesupportinginformationS6).Therefore,allparticleswillmovetowardsﬁeldmaxima126whicharelocatedattheedgesoftheelectrodearrayonthePCBs.Asthesizesofthe127particlesheredivergesigniﬁcantly,weaimtoexploitthelinearvolumedependenceofFDEP128toachieveaseparation.129ThesizediﬀerencesofgraphiteandLiFePO4particlesarecriticalforasizedependent130sortingasitisconductedinthisstudy.Thisdiﬀerencemaybeaﬀectedbyanupstream131liberationstepthatproducesblackmass.This,however,dependsstronglyontheliberation132stepitself.Muetal.47describedforcathodematerial,hereLiCoO2,noapparentsizechanges1337 whenliberatingtheparticleswithcalcinationorsupercriticalCO2.Theliberationofparticles134fromblackmassduringtherecyclingofspentLIBsisaseparateﬁeldofresearchandnot135partofthisstudy.Artiﬁcialblackmassisusedheretoexcludeeﬀectsupstreamprocesses,136focusonseparabilityunderidealconditionsandfacilitatereproducibility.137Table1:ParametersdescribingthesizedistributionoftheusedparticlesParticled10/µmd50/µmd90/µmLiFePO40.61.56.0KS61.53.46.1Actilion1317232.3Measurementsystem138Twomethodswereusedtomeasuretheparticleseparation.Qualitatively,thetotalparticle139concentrationwasmeasuredbywhite-lightreﬂectioninreal-timeattheoutlet.Quanti-140tatively,theLiFePO4concentrationwasfurtherevaluatedusingphotometricdetectionof141dissolvedironmass.ThereﬂectionmeasurementsystemisdescribedinRef.25.Brieﬂy,it142consistsofaspectrometer(Silvernova,StellarNet,Inc.,USA)andaﬂowcuvette(176-765-14385-40and176-760-85-40,HellmaGmbH&Co.KG,Germany).Awhitelightsource(XCite144120PC,ExcelitasTechnologiesCorp.,USA)isconnectedin90◦withrespecttothelight145guideofthespectrometer.Particlesintheﬂowcuvettewillscatterthelightandproduce146asignalthatcanberecordedbythespectrometer.Forsize-distributedparticlesystems,147itisimportanttokeepinmindthatthereﬂectionintensityvarieswithparticlesize.For148spheresinthesizerangeoftheparticlesusedhereandthewavelengthofthelightsource,149thescatteringintensityisproportionaltor2p.48Astheparticlesherearenotperfectspheres150(Figure2),thesignalrecordedbythespectrometerdoesnotprovidetheinformationofthe151numberormassofelutedparticles,whichisdiﬀerentcomparedtomonodisperseparticulate152systemsasinRef.25and22.Thiscertainlyisadownsideofthereﬂectionmeasurement153setup.Wethususethemeasuredreﬂectivelightintensityreductionattheoutletasaqual-154itativereal-timeindicatorofparticleretention.TomeasuretheretentionofLiFePO4inthe1558 ﬁlter,weusedachemicalprocedurewhichallowsaphotometricdeterminationoftheiron156mass.TheprocedurewasderivedfromDIN38406(seesupportinginformationS5).Brieﬂy,157theLiFePO4particlesaredissolvedinanacidandtheironcontentisdeterminedusinga158complexingagentandperformingaphotometricmeasurementafterward.491592.4Experimentalprocedure160Experimentswerecarriedoutinalow-conductivitymedium(2.1µS/cm)consistingofpure161water(Omniatap6UV/UF,stakpureGmbH,Germany),0.01vol.%Tween20(Sigma–Aldrich,162Germany),andKCltoadjusttheconductivity.Alowconductivitymediumwasselectedas163thisreducestheinﬂuenceofthermaleﬀects.Forfutureapplications,theimpactofanin-164creasedconductivityneedstobeinvestigatedasthismayhaveanimpactontheseparation.165Theblackmassusedinthisstudyisartiﬁcial.Consequently,theimpactofresidualsfroman166upstreamprocessthatproducesactualblackmassisnotconsideredandbeyondthescopeof167thisstudy.Tocreateparticlestocksuspensions,theparticlesweresuspendedinan1vol.%168aqueousTween20suspensionwith4g/LforLiFePO4andKS6and12g/LforActilion.The169LiFePO4suspensionwasrenewedeverythreedaysasLiisknowntodissolvetoalowextend170intoaqueoussolutions,50andwewantedtoexcludethiseﬀectfromourexperiments.Prior171totheexperiments,wesonicatedtheparticlestocksuspensionsandadded0.22vol.%ofit,172forLiFePO4andKS6,intothemediumfortheexperiments.Inordertoachieveasuﬃcient173reﬂectionsignal,wehadtoincreasetheActilionconcentration,resultingina10×higher174totalmassofActilionintheﬁnalsuspensioncomparedtotheothertwoparticletypes.The175reasonbehindthismightbelowerspeciﬁcsurfaceareaofthelargerActilionparticlesand176thuslowerreﬂectanceperaddedmass.177Thesuspensionswerestirredthroughouttheentireexperiment.Tosubtracttheback-178groundsignal,werecordedtheintensitysignaldailywithnoparticlespresent(supporting179informationS2).Atthebeginningoftheexperimentswemeasuredtheinitialreﬂection180signaloftheparticlesuspensionfor30s.At30stheelectricﬁeldwasturnedonfor270s.1819 Afterthevoltagewasturnedoﬀ,theexperimentwasfurthermonitoreduntiltheinitialin-182tensitywasobtainedagain.Sometimes,theinitialsignalwasnotfullyreachedduetoeﬀects183suchassedimentationorbubbleadhesionintheﬂow-throughcuvette.Asaconsequencewe184ﬂushedtheentiresetupatahighﬂowrateaftereverytwoexperiments.Everydatapoint185representsthreeexperiments.Equation1insectionS1ofthesupplementdetailshowthe186signalreductioniscalculated.187TochemicallydeterminetheretentionoftheLiFePO4particles,wecollected4mLof188suspensionina5mLcontainer.Thesamplesweretakenatthebeginningoftheexperiment,189startingafter5sandduringthetrapping,startingafter200s.Inordertoobtainasuﬃcient190samplevolumeatthebeginningoftheexperiment,thevoltagewasturnedonafter60s.191Alldatafromthereﬂectionmeasurements,theevaluationscript(MATLAB,detailssee192supportinginformationS1)andPCBmanufacturingdataareuploadedtoanonlinereposi-193tory(Ref.51).1943ResultsandDiscussion1953.1Frequencydependentbehaviorupto500kHz196AllparticlesinthisstudyareconductiveandthusshouldshowpDEP.Totestthishypothesis,197weconductedexperimentsat30Vppfrom1kHzto500kHzatavolumeﬂowof6mLmin−1198withonlyoneparticletypepresentperexperiment(Figure3).Higherfrequencieswere199notapplicableinthissetupandtheselectedvoltage,becausetherequiredcurrentwould200exceedthemaximumoftheampliﬁer.Forallparticlesthetrappingeﬃciency(measured201qualitativelyintermsofreductionofreﬂectivelightintensitysignal,calledsignalreduction)202washighestat500kHzandsigniﬁcantlyhigherthanatlowerfrequencies.Thismightbe203becausedisturbingelectrokineticeﬀectslikeACelectroosmosiscanbedominantatlower204frequencies.52However,asthefrequencysigniﬁcantlyexceedstheelectrothermalhydrody-205namicrelaxationfrequency(f=σm/(2πεm)≈48kHz),thiseﬀectshouldbenegligible.5320610 Figure3:FrequencydependencyofthesignalreductionofAcilion,KS6andLiFePO4sus-pensionsat6mLmin−1and30Vpp.Frequencieswerevariedbetween1kHzand500kHz.Currently,wearenotsurewhatiscausingthereproduciblefurthertrappingincreaseand207thussignalreductionwithanadditionalincreaseinfrequency.Nonetheless,signiﬁcantdif-208ferenceinthesignalreductionbecomesapparentwhencomparingtheparticletypes.Thisis209likelycausedbythediﬀerencesinparticlessizeasDEPscaleswithparticlevolume(Equation2102).Forexample,at30Vppand500kHz,Actilionshowsahighsignalreductionof93±0.6%211butthesignalofLiFePO4isonlyreducedby26±1.5%.Tofurtherinvestigatethebe-212havioroftheparticles,weselected500kHzasfrequencyforallsubsequentexperiments,213becausetheperformanceofthedeviceisthehighestatthisfrequencyandDEPthedomi-214natingforce.Wenotethatadirectquantitativecomparisonbetweenthediﬀerentparticles215typesmaybemisleading.Thisisbecausethescatterpropertiesbetweendistributedparti-216clesamplesmaybediﬀerentduetodiﬀerentshapes.Thequalitativecomparison,however,217revealssigniﬁcantdiﬀerencesthatagreewellwiththeproposedsizeselectivity.Theappli-218cationof500kHzalsodemonstratesthatfrequenciesinthisrangecanbeappliedinahigh219throughputdevice.Comparedtoprevioushigh-throughputapproachesbyourgroup22–24220thatwereinsulator-basedDEPdevices,theapplicablefrequencybandwidthwasexpanded22111 from75kHzto500kHzwhilemaintainingthepossibilityofapplyinghighvolumeﬂows.A222higherpossiblefrequencycanbebeneﬁcialwhendesigningtheprocessaswithincreasing223frequencythepolarizabilitycanalterandenableaseparation.Inapreviousstudywecould224showthatretentionduetonDEPissmall(<10%)insuchasetupandthereforeisnotthe225reasonforourobservations.252263.2Inﬂuenceofvoltageandvolumeﬂow227Assecondstep,weinvestigatedtheinﬂuencevoltageonsignalreductionfrom5to75Vpp228at6mLmin−1(Figure4A)and10mLmin−1(Figure4B).Atbothﬂowrates,allparticles229showanincreasedsignalreductionorparticleretentionwithincreasingvoltage.Thisisin230linewiththeapproximationoftheDEPforce(Equation2).Additionally,increasingvolume231ﬂowdecreasesthesignalreduction.Thisisduetotheincreasedviscousdraganddecreased232residencetimeinthesetupatthehigherﬂowrate.Thedataat6mLmin−1and30Vpp233isthesameasinFigure3,exceptforActilion.Here,weusedadiﬀerentﬂowcuvettefor234thismeasurementstopreventsedimentation.However,theresultsarequitesimilar(here23597±2.7%comparedto93±0.6%).Figure4C-Eshowsintensityplotsovertimeforall236particlesat30Vppand10mLmin−1.ThreethingsbecomeapparentfromFigure4.First,237thesignalreductionofActilionissigniﬁcantlyhigherthanthatofLiFePO4.Forexample,at23830Vppand10mLmin−1(Figure4B,CandE),thesignalreductionofActilionisoverfour239timeshigherthanitisforLiFePO4.Here,therecordedintensityforActilionisclosetozero,240indicatingacompleteremoval.TherelativediﬀerenceofthesignalreductionofLiFePO4241andActilion,however,decreaseswithincreasingvoltage(Figure4AandB).Likely,thisis242becauseActilionisalreadyalmostcompletelyremovedatvoltagesover30Vppatbothﬂow243rates,whereasLiFePO4removalincreaseswithvoltagefrom0to75Vpp.Second,KS6also244showssigniﬁcanttrappingandgetsfullyremovedatabout75Vppatbothﬂowrates.Third,245thereﬂectionmeasurementscancreatesignalreductionslightlyhigherthan100%whichis246linkedtothesubtractionofthebackgroundsignalandwasobservedbefore.25Thehighest24712 Figure4:VoltageandvolumeﬂowdependencyofthesignalreductionforActilion,KS6andLiFePO4suspensionsatafrequencyof500kHz.Thebehaviorwasevaluatedbetween5and75Vppat6mLmin−1(A)and10mLmin−1(B).Asexample,normalizedreﬂectionintensitiesovertimeforallmaterialsat30Vppand10mLmin−1arealsoshown(C-E).Forallexperiments,thesignalreductionwasmeasuredbetween200and300s(C).Thevoltagewasappliedafter30sfor270s(D).13 recordedvaluewas104±1.5%at10mLmin−1and30Vpp.Asthedeviationisexplainable248(supportinginformationS2),relativelysmall,andshowingacompleteremovalofActilion,249wedonotconsiderthisproblematic.250Insummary,thesize,voltage,andvolumeﬂowdependencyofthesignalreductionfor251theseparticleswasasexpected.Inaddition,weobservedanalmostcompleteremovalof252Actilionfromthesuspensionstartingat30Vpp.FormixturesofLiFePO4andActilion,253thiswouldcorrespondtoapurefractionofLiFePO4attheoutletandanenrichmentof254Actilionwithintheﬁlter.Highervoltagesthan30Vppwouldnotleadtoasigniﬁcantly255increasedtrappingofActilionbuttomoreretainedLiFePO4.Therefore,weselected30Vpp256forseparationexperimentsofActilionandLiFePO4. Figure5:A:VariationofthemassratioofLiFePO4andActiliongraphiteparticlesinthesuspensionat30Vpp,500kHzand6mLmin−1.B:Comparisonofreﬂectionmeasurementsofsuspensionswithonlyoneparticletypepresent(dottedlines)andthechemicalanalysisofLiFePO4removalfromamixturewith10timesmoremassofActilionthanLiFePO4(dashedline).2573.3BehaviorinamixtureofgraphiteandLiFePO4258Asaﬁnalstep,weinvestigatedtheseparabilityofamixtureofLiFePO4andActilion.259WedidnotincludeKS6becauseconductiveadditivesareonlyaround4%ofthebattery26014 mass.2Itwouldfurtherincreasethediﬃcultyofanalyzingtheresultsbecausethereﬂection261measurementisnotmaterialsensitive.Wetriedtocalculateseparatereﬂectionspectrafor262eachcomponentbysuperpositionofthereﬂectionspectraofpureLiFePO4andActilion,263astheyareslightlydiﬀerent.Forﬂuorescentparticlesthiscanbeachievedbycoupling264these