锂枝晶形成机理

MechanismsofdendriticgrowthinvestigatedbyinsitulightmicroscopyduringelectrodepositionanddissolutionoflithiumJensSteigera,DominikKramerb,*,ReinerMöniga,baKarlsruheInstituteofTechnology(KIT),InstituteforAppliedMaterials(IAM),Hermann-von-Helmholtz-Platz1,76344Eggenstein-Leopoldshafen,GermanybHelmholtzInstituteUlm(HIU)ElectrochemicalEnergyStorage,Albert-Einstein-Allee11,89081Ulm,Germanyhighlightsgraphicalabstract
Weobtaininsituvideosattheopticalresolutionlimitinacommercialelectrolyte.
LineedlescangrowsimultaneouslyatthesubstrateeLiinterface,atkinksortips.
Dissolutionthinslithiumneedles;aSEIshellremains;tipsstayinactive.
Theobservationsarenotcompatiblewithknownmechanismsofdendriticgrowth.
Anewmechanismofinsertionatdefectsissuggested.articleinfoArticlehistory:Received26November2013Receivedinrevisedform3March2014Accepted7March2014Availableonline21March2014Keywords:LithiummetalBatteryElectrodepositionDendriticgrowthGrowthmechanismOpticalimagesabstractBatterieswithmetalliclithiumanodesofferimprovedvolumetricandgravimetricenergydensities;therefore,futurebatteriesincludingthepromisinglithiumesulfurandlithiumeairsystemswouldbenefitfromthem.Theelectrodepositionoflithiummetalewhichisanunwantedincidentinlithiumionsystemseoftenresultsinfinefilamentsormoss,calleddendriticlithium,whichleadstostrongcapacityfadingandthedangerofinternalshortcircuiting.Tostudythemechanismsofdendriticgrowthandthebehaviorduringlithiumdissolution,lithiumdepositshavebeenobservedinsituin1MLiPF6inEC:DMCbylightmicroscopy.Thehighresolutionopticalmicroscopyprovidedinformationonthegrowthandelectrodissolutionofsinglelithiumfilaments.Thegrowthareascouldbeidentifiedindetail:Thelithiumwirescangroweitherfromthesubstrateelithiuminterface,atkinksorinaregionatorclosetothetip.Basedontheseobservations,wesuggestagrowthmodelforlithiumfilamentspredicatedondefect-basedinsertionoflithiumattheaforementionedlocations.Thistypeofgrowthisnotcompatiblewithpreviousmodelsofdendriticgrowth,forexample,itishardlyinfluencedbyelectricfieldsatthetipanddoesnotdependonthedirectionoftheelectricfield.
2014ElsevierB.V.Allrightsreserved.1.IntroductionLithium-ionsecondarybatteriesarethestateofthearttech-nologyforportableelectricenergystorage.Theyhavetakenaleadingroleinthepowersupplyofmobileelectronicsandofelectriccars.Thisisduetotheirhighenergyandpowerdensities.Lithium-ionbatteriesusuallyusegraphiticanodesandintercala-tionmaterialsascathodes[1].Theuseofpurelithiummetalinsteadofgraphitestronglyim-provesthevolumetricandspecificenergydensityofcells.Lithiummetalelectrodeshavethelowestelectrochemicalpotentialandasuperiorspecificcapacity;theyarerequiredtotakefulladvantage*Correspondingauthor.Tel.:þ4972160824894;fax:þ497315034009.E-mailaddress:[e-mail](D.Kramer).ContentslistsavailableatScienceDirectJournalofPowerSourcesjournalhomepage:://dx.doi.org/10.1016/j.jpowsour.2014.03.0290378-7753/
2014ElsevierB.V.Allrightsreserved.JournalofPowerSources261(2014)112e119ofpossiblefuturetechnologiessuchasLieSorLieO2cells.Whilepurelithiummetalanodesarecommoninprimarybatteries,theso-calledlithiumdendritegrowthduringchargeisthemainin-hibitoroftheusageofthoseanodesinsecondarybatteries.Eventhoughtoday’slithium-ionbatteriesdonotcontainmetalliclithium,theycanstillsufferfromdendritegrowthforhighratesofchargingespeciallyatlowtemperatures.Theterm“dendrite”isusedindifferentareasoftechnologyandscience,suchasmetallurgyandmineralogy,torefertoabranched,tree-likestructurewhichforexamplecanbeformedbysolidifica-tionfromaliquidphase.Duringelectrodepositionofmetals,den-driticgrowthisverycommonandtheissueofdendriticgrowthduringbatterycharginghasbeendiscussedindetailalreadyde-cadesago,e.g.inRef.[2].Forthecaseoflithiumplatingthough,dendriticdepositionoccursatcomparativelylowcurrents[3].Thephenomenonofdendriticgrowthoflithiumisknownsincethe1960s[4]orearly1970s[5]butsofaronlylimitedunder-standingofthisprocessexists.Severalmodelsandexplanationshavebeenproposedandsomewillbepresentedinthefollowing,butasofnownogeneralagreementonthebasicgrowthmecha-nismisreached.Cohenetal.[6]proposedamodelthatfocusesonthecompli-catednatureofsolid-electrolyteinterphase(SEI)formation.Theyarguethatinanon-aqueoussolution,theSEIe“beingamosaic-type,multilayeredstructure,duetothelargevarietyofpossiblesurfacereactions”eisintrinsicallynon-uniforminthenanometerandeveninthemicrometerscale.ThiscauseslocalizeddepositionanddissolutionatpartsoftheSEIthathaveahigherion-conductivityduetotheirsmallerthicknessormoreion-conductivecomposition.ThiscausesstressbetweentheshapechanginglithiumlayerandtheSEIontop.Forhighcurrentden-sities,theSEImightnotbeabletowithstandtheinducedstressandcracks,whichrevealsanareaofthelithiumwithoutSEI,whichwillincreasethelocalizationevenfurther.Duringdissolution,theinhomogeneouscurrentdistributioncausesdeeppitsinthelithium,andforplatingthiscanbethecausefordendriticgrowth.Anotherimportantfactorcanbetheionicconcentrationgradientintheelectrolyte.Duringdeposition,theconcentrationofmetalcationswilldropatthenegativeele