Separator-Shutdown-Test-Procedure

1ProcedureforDeterminingShutdownTemperatureofBatterySeparatorsBackgroundLamanetal.[1]werethefirsttodeterminetheelectricalimpedanceofbatteryseparatorsasafunctionoftemperature(from25-200oCatascanrateof1oC/min).Theyfoundtheimpedanceincreasedbyseveralordersofmagnitudenearthemeltingpointoftheseparator,butthenrapidlydroppedtonearzero.Bystackinglayersofpolyethyleneandpolypropylenemembranestogethertheywereabletomaintainahighimpedanceoverthetemperaturerangecorrespondingtothemeltingpointsofpolyethylene(135oC)andpolypropylene(165oC).TheseresultswereverifiedbyGeigeretal.[2]usingsteady-statemeasurementsinathermally-stableelectrolyte.Spotnitzetal.[3]extendedtheprocedureofLamanetal.[1]toallowfasterscanrates(~60oC/min)usingthethermally-stableelectrolyteofGeigeretal.[2].MaterialsRequired1)RLCmeterwithdigitaloutputtodataacquisitionsystem.TheRLCbridgeshouldbecapableofprovidingimpedancevaluestothedataacquisitionsystematarateofatleast10perminute.2)Dataacquisitionsystem(forexample,LabView)forrecordingtemperatureandimpedance.3)Heatedpress(example,Carverwithhigh-powerheaters)andtemperaturecontroller(example,EurothermequippedforRTDs).Optionally,ainsertablecoolingmeansforthepresscanbeusedtoallowforfasterturnaroundbetweentests.4)Cell(seeattachment)5)Electrolyte–1Mlithiumtrifluoromethanesulfonimide(HQ-115,3MCo.)ina1:1byvolumesolutionofpropylenecarbonateandtriethyleneglycoldimethylether.Theelectrolyteshouldbestoredinadrybox.6)Twofastresponse,microRTDs.ExperimentalFigure1showsaschematicoftheexperimentalarrangement.Theexperimentshouldbecarriedoutinafumehood.TwoRTDtemperaturesensorsareincludedinthetestcell.ThetemperaturecontrollerusesoneoftheRTDswhiletheotherisusedasacheck.ThereadingsfrombothRTDsshouldberecordedbythedataacquisitionsystem,aswellastheoutputfromtheRLCmeter.Theprocedureforcarryingoutthetestisasfollows.1)Placeafewdropsofelectrolyteontotheseparatortosaturateit,andplacetheseparatorintothetestcell.22)Makesurethattheheatedpressisbelow50oC,andifso,placethetestcellbetweentheplatensandcompresstheplatensslightlysothatonlyalightpressureisappliedtothetestcell(50lbsforaCarver“C”press).3)ConnectthetestcelltotheRLCbridgeandbeginrecordingtemperatureandresistance.Whenastablebaselineisattained,thenstartrampingthetemperatureofthepressat10oC/minusingthetemperaturecontroller.4)Turnofftheheatedplatenswhenthemaximumtemperatureisreachedorwhentheseparatorimpedancedropstoalowvalue.5)Opentheplatensandremovethetestcell.Allowtestcelltocool.Removeseparatoranddisposeof.Figure1ExperimentalArrangementforShutdownTemperatureTest.DataAcquisitionRLCMeterTemp.ControllerDataAcquisitionRLCMeterTemp.ControllerDataAcquisitionRLCMeterTemp.ControllerResultsTheresultsshouldbereportedgraphicallyonsemi-logpaperplottingthelogoftheimpedance(ohm-cm2)versustemperature(oC).ThetemperaturevaluereportedshouldbetheaverageofthetwoRTDreadings.Normally,theimpedancewillincreasefromitsinitialvaluetosomemaximumvalue,stayatthatmaximumvalueoveralimitedtemperaturerange,andthendecreasetoavaluelowerthantheinitialvalue.Shutdownoccursiftheimpedancemaximumisatleast100Xgreaterthantheinitialimpedancevalue.Somewhatarbitrarily,theshutdowntemperature,TSD(oC),isdefinedasthetemperatureatwhichtheimpedancefirstrisesto100Xitsinitialvalue.Thetemperatureatwhichtheimpedancefirstdropsto100Xitsinitialvalueisdefinedasthemeltintegritytemperature,TMI(oC).Theshutdownwindowisdefinedasthedifferencebetweenthesetwotemperatures(=TSD-TMI).3References:[1]F.C.Laman,M.A.Gee,J.Denovan,“ImpedanceStudiesforSeparatorsinRechargeableLithiumBatteries”,J.Electrochem.Soc.,Vol.140No.4,April1993p.L51-L53.[2]P.Geiger,R.Callahan,C.Dwiggins,H.Fisher,D.Hoffman,W.-C.Yu,K.Abraham,M.Jillson,T.Nguyen,“AdvancedSeparatorsforLithiumBatteries”,The11thIntl.Sem.Primary&SecondaryBatteryTechnologyandApplications,1994.[3]R.Spotnitz,M.Ferebee,R.Callahan,K.Nguyen,W.-C.Yu,M.Geiger,C.Dwiggins,H.Fisher,D.Hoffman,“ShutdownBatterySeparators”,The12thIntl.Sem.Primary&SecondaryBatteryTechnologyandApplications,1995.AttachmentDesignandConstructionofTestCellThetestcellcanbeconstructedfromcommerciallyavailablematerials(Kaptonfilmandtape,nickelfoil,steelplates,).CutoutapieceofKaptonfilm(2milthick)3incheswideby8incheslong.Foldthefilmaboutthemidpointofthelengthsotwolayersoffilmresultthatareeach4incheslong.Puncha¼”holeinthroughbothlayersoffilmapproximately2”awayfromthefoldandcenteredaboutthewidth.Alsopunchouttwo¼”diameterdisksfroma2milnickelfoilandspotweldontothenickelfoilsleadsconsistingofnickelfoil(1/8”wide8”long).ForceeachnickeldiskintotheholesintheKaptonfromoutsideofthebend(seeFigureA1).InsulatetheexposednickelusingKaptontape.FigureA1summarizesthisprocess.ThebendintheKaptonfilmservesasahingetoopenthelayersandallowtheseparatortobeinsertedbetweenthetwonickelelectrodes.FigureA1Constructionoftestcell.Nottoscale.TopViewSideView4Thecellshouldbeplacedinafixtureconsistingoftwosteelplates(1/8”thick,5”wide,6”long).Inoneoftheplates,groovesshouldbemadetoplacetheRTDs.FigureA2BottomsteelplatetoholdtestcellandRTDs.Nottoscale.TopViewSideViewTopViewSideViewSideViewwithtestcellB