锂枝晶形成机理

1、MechanismsofdendriticgrowthinvestigatedbyinsitulightmicroscopyduringelectrodepositionanddissolutionoflithiumJensSteigera,DominikKramerb,*,ReinerMöniga,baKarlsruheInstituteofTechnology(KIT),InstituteforAppliedMaterials(IAM),Hermann-von-Helmholtz-Platz1,76344Eggenstein-Leopoldshafen,GermanybHelmholtzInstituteUlm(HIU)ElectrochemicalEnergyStorage,Albert-Einstein-Allee11,89081Ulm,GermanyhighlightsgraphicalabstractWeobtaininsituvideosattheopticalresolutionlimitinacommercialelectrolyte.Lineedlescang。

2、rowsimultaneouslyatthesubstrateeLiinterface,atkinksortips.Dissolutionthinslithiumneedles;aSEIshellremains;tipsstayinactive.Theobservationsarenotcompatiblewithknownmechanismsofdendriticgrowth.Anewmechanismofinsertionatdefectsissuggested.articleinfoArticlehistory:Received26November2013Receivedinrevisedform3March2014Accepted7March2014Availableonline21March2014Keywords:LithiummetalBatteryElectrodepositionDendriticgrowthGrowthmechanismOpticalimagesabstractBatterieswithmetalliclithiumanodesofferimp。

3、rovedvolumetricandgravimetricenergydensities;therefore,futurebatteriesincludingthepromisinglithiumesulfurandlithiumeairsystemswouldbeneﬁtfromthem.Theelectrodepositionoflithiummetalewhichisanunwantedincidentinlithiumionsystemseoftenresultsinﬁneﬁlamentsormoss,calleddendriticlithium,whichleadstostrongcapacityfadingandthedangerofinternalshortcircuiting.Tostudythemechanismsofdendriticgrowthandthebehaviorduringlithiumdissolution,lithiumdepositshavebeenobservedinsituin1MLiPF6inEC:DMCbylightmicroscopy.T。

4、hehighresolutionopticalmicroscopyprovidedinformationonthegrowthandelectrodissolutionofsinglelithiumﬁlaments.Thegrowthareascouldbeidentiﬁedindetail:Thelithiumwirescangroweitherfromthesubstrateelithiuminterface,atkinksorinaregionatorclosetothetip.Basedontheseobservations,wesuggestagrowthmodelforlithiumﬁlamentspredicatedondefect-basedinsertionoflithiumattheaforementionedlocations.Thistypeofgrowthisnotcompatiblewithpreviousmodelsofdendriticgrowth,forexample,itishardlyinﬂuencedbyelectricﬁeldsatthetip。

5、anddoesnotdependonthedirectionoftheelectricﬁeld.2014ElsevierB.V.Allrightsreserved.1.IntroductionLithium-ionsecondarybatteriesarethestateofthearttech-nologyforportableelectricenergystorage.Theyhavetakenaleadingroleinthepowersupplyofmobileelectronicsandofelectriccars.Thisisduetotheirhighenergyandpowerdensities.Lithium-ionbatteriesusuallyusegraphiticanodesandintercala-tionmaterialsascathodes[1].Theuseofpurelithiummetalinsteadofgraphitestronglyim-provesthevolumetricandspeciﬁcenergydensityofcells.Li。

6、thiummetalelectrodeshavethelowestelectrochemicalpotentialandasuperiorspeciﬁccapacity;theyarerequiredtotakefulladvantage*Correspondingauthor.Tel.:þ4972160824894;fax:þ497315034009.E-mailaddress:dominik.kramer@kit.edu(D.Kramer).ContentslistsavailableatScienceDirectJournalofPowerSourcesjournalhomepage:://dx.doi.org/10.1016/j.jpowsour.2014.03.0290378-7753/2014ElsevierB.V.Allrightsreserved.JournalofPowerSources261(2014)112e119ofpossiblefuturetechnologiessuchasLieSorLieO2cells.Whilepurelithiummetalano。

7、desarecommoninprimarybatteries,theso-calledlithiumdendritegrowthduringchargeisthemainin-hibitoroftheusageofthoseanodesinsecondarybatteries.Eventhoughtoday’slithium-ionbatteriesdonotcontainmetalliclithium,theycanstillsufferfromdendritegrowthforhighratesofchargingespeciallyatlowtemperatures.Theterm“dendrite”isusedindifferentareasoftechnologyandscience,suchasmetallurgyandmineralogy,torefertoabranched,tree-likestructurewhichforexamplecanbeformedbysolidiﬁca-tionfromaliquidphase.Duringelectrodepositio。

8、nofmetals,den-driticgrowthisverycommonandtheissueofdendriticgrowthduringbatterycharginghasbeendiscussedindetailalreadyde-cadesago,e.g.inRef.[2].Forthecaseoflithiumplatingthough,dendriticdepositionoccursatcomparativelylowcurrents[3].Thephenomenonofdendriticgrowthoflithiumisknownsincethe1960s[4]orearly1970s[5]butsofaronlylimitedunder-standingofthisprocessexists.Severalmodelsandexplanationshavebeenproposedandsomewillbepresentedinthefollowing,butasofnownogeneralagreementonthebasicgrowthmecha-nismisr。

9、eached.Cohenetal.[6]proposedamodelthatfocusesonthecompli-catednatureofsolid-electrolyteinterphase(SEI)formation.Theyarguethatinanon-aqueoussolution,theSEIe“beingamosaic-type,multilayeredstructure,duetothelargevarietyofpossiblesurfacereactions”eisintrinsicallynon-uniforminthenanometerandeveninthemicrometerscale.ThiscauseslocalizeddepositionanddissolutionatpartsoftheSEIthathaveahigherion-conductivityduetotheirsmallerthicknessormoreion-conductivecomposition.Thiscausesstressbetweentheshapechangingli。

10、thiumlayerandtheSEIontop.Forhighcurrentden-sities,theSEImightnotbeabletowithstandtheinducedstressandcracks,whichrevealsanareaofthelithiumwithoutSEI,whichwillincreasethelocalizationevenfurther.Duringdissolution,theinhomogeneouscurrentdistributioncausesdeeppitsinthelithium,andforplatingthiscanbethecausefordendriticgrowth.Anotherimportantfactorcanbetheionicconcentrationgradientintheelectrolyte.Duringdeposition,theconcentrationofmetalcationswilldropatthenegativeele。