582S.K?bitzetal./JournalofPowerSources239(2013)572e583
[a]
908070605040302010020lifetime/yearsCapacitive lifetime (C= 70%)
[b]
3530lifetime/years252015105020
100% SOC90% SOC80% SOC50% SOC20% SOCResistive lifetime (R= 200%)
100% SOC90% SOC80% SOC50% SOC20% SOC40
60T/°C
8010040
60T/°C
80100
Fig.17.Capacitylifetime(endoflife(EOL)criterion:Cact?70?OT)(a)andresistivelifetime(EOLcriterion:Ract?200%RBOT)vs.temperatureforcalendarlifetestsatdifferentcellvoltagelevels.
lifetimebecomes85years,resistivelifetime32years.Onecanarguethatthesenumbersarenotrealistic,butithastobekeptinmindthatthesquarerootoftimeapproachforthelifetimeextrapolationonlyaccountsfortheinternalagingmechanismsofSEIformation.Allotheragingmechanismslikeleakageorlossofelectrolytee.g.causedbypouchbagrupture,orelectrodeirreversiblelossduetoactivematerialdegradationarenotincludedinthisapproach.Furthermore,usingasquarerootapproach,scatteringinthetestdatain?uencesthepredictedlifetimequitealot.Neglectingthecellwithlowestcapacitydegradationinthetestwithcellsstoredat25??Cand50%SOCatCVleadstoacapacitylifetimeof56years,incomparisonto85years,ifallthreecellsareconsideredinthe?tting.Inadditiontothelimitationsonlifetimepredictionsmentionedbeforeithastobeassured,thattheagingin?uenceissigni?cantlyhigherthanthescatteringofthecellsinonetestset,whichismostlythecaseforhighertemperaturesleadingtohighercapacitylossandresistanceincrease.Usingtheseacceleratedagingtestshasthedisadvantageofpossiblytriggeringagingprocesseswhichareun-likelytohappeninrealapplications.TheseadditionalagingeffectsathighertemperatureswouldalsoinvalidatetheArrheniusextrapolationofthetestdatatolowertemperatures.Ifthementionedlimitationsofthisapproachareconsidered,itcanbeusedforlifetimeestimationofhighqualitycells,wheremoderateSEIevolutionisthemainagingmechanism[13].4.ConclusionAnextensiveagingstudyofagraphitejLiNi1/3Mn1/3Co1/3O2(NMC)Li-ionpouchcellhasbeenpresentedinthisworkbasedonreferenceparameterteststodeterminetheagingbehavior.Calen-darlifetestsatdifferentvoltagesandtemperatureshavebeenconductedaswellascyclingtestsatdifferentaverageSOCandcycledepths.Thetemperaturedependencycouldbeidenti?edasArrheniustypeandactivationenergiescouldbedetermined,whichareingoodaccordancetotheliterature.Thevoltagedependencybetween50%and90%SOCisrathersmall.However,storingthecellsat20%SOCcanbeevenbene?cialforcapacity,whichcanalsobeobservedinatestwithalternatingvoltagelevels.Thiseffectseemstobetemperatureindependent.AcomparisonbetweencalendarlifeagingatOCandCVshowedsigni?cantdifferencesonlyat100%SOCincapacitydecline.Thisiscausedbytherelativesmalldependencyoftheagingoncellvoltagebelow100%SOC.ThereforedeviationsfromthesetlowerSOCintheOCtestsduetoself-dischargeareofminorimportance.SEIformationontheanodeisexpectedtobethemainagingmechanismforcalendarlifetests,causingasquarerootoftimeshapedagingbehavior.Theagingbehaviorofcyclingtestshasbeenidenti?edasdependentontemperatureandcycledepth.Cyclingtestsat10%DODshowacapacitydeclineequaltocalendarlifeagingtests.HigherDOD(50%andfullcycling)ledtoincreasedadditionalcapacityfade.Acompleximpactofcyclingonresistanceincreasehasbeenobserved.AtT?25??CandhighDODtherewasevenasmallerresistanceincreasethaninthecorrespondingcalendarlifetest.Takingresultsfrompost-mortemanalysisfrompaperpartBintoaccount,theresistanceforcyclicagingappearstobedependedontheinteractionofvolumeincreaseanddepositionreactionsontheanodeside.Furtherstudiesincludingpost-mortemanalysisinpaperpartBandEISwillbepresentedinseparatepublicationsforclari?cationoftheoccurringagingef-fects.Moredataandanin-depthanalysisofthecyclingtestswillfollowaswell.AcknowledgmentsThisworkwassponsoredbytheGermanFederalMinistryofEducationandResearch(BMBF)undercontractno.03X4613Gaspartoftheprogram“LIB2015”.TheauthorsaregratefultoConti-nentalandDaimlerfortheirassistancetothisstudyaspartnersofthisproject.SpecialthanksgotoZSWforprovidingresultsfrompost-mortemanalysis.References[1]M.Wachtler,M.K?nig,M.Kasper,M.Fleischhammer,B.Emmermacher,P.Axmann,M.Wohlfahrt-Mehrens,J.PowerSources,submittedforpublication.[2]M.Safari,M.Morcrette,A.Teyssot,C.Delacourt,J.Electrochem.Soc.156(2009)A145eA153.[3]M.Ecker,J.B.Gerschler,J.Vogel,S.K?bitz,F.Hust,P.Dechent,D.U.Sauer,J.PowerSources215(2012)248e257.[4]M.Broussely,S.Herreyre,P.Biensan,P.Kasztejna,K.Nechev,R.Staniewicz,J.PowerSources97e98(2001)13e21.[5]G.Ning,B.Haran,B.N.Popov,J.PowerSources117(2003)160e169.[6]J.Shim,K.A.Striebel,J.PowerSources122(2003)188e194.[7]R.Wright,C.Motloch,J.Belt,J.Christophersen,C.Ho,R.Richardson,I.Bloom,S.Jones,V.Battaglia,G.Henriksen,T.Unkelhaeuser,D.Ingersoll,H.Case,S.Rogers,R.Sutula,J.PowerSources110(2002)445e470.[8]I.Bloom,B.Cole,J.Sohn,S.Jones,E.Polzin,V.Battaglia,G.Henriksen,C.Motloch,R.Richardson,T.Unkelhaeuser,D.Ingersoll,H.Case,J.PowerSources101(2001)238e247.[9]J.Wang,P.Liu,J.Hicks-Garner,E.Sherman,S.Soukiazian,M.Verbrugge,H.Tataria,J.Musser,P.Finamore,J.PowerSources196(2011)3942e3948.[10]M.Kassem,J.Bernard,R.Revel,S.Pélissier,F.Duclaud,C.Delacourt,J.PowerSources208(2012)296e305.[11]I.Bloom,L.K.Walker,J.K.Basco,D.P.Abraham,J.P.Christophersen,C.D.Ho,J.PowerSources195(2010)877e882.S.K?bitzetal./JournalofPowerSources239(2013)572e583
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