CHEMO-MECHANICAL MODELLING OF FRACTURE IN HETEROGENEOUS CATHODE FOR LITHIUM-ION BATTERY

Abstract

Next-generationcathodesforlithium-ionbatteries(LIB)arecomposedofthepolycrystalline microstructure havingmulti-layeredthinfilmarchitectureorthecompositeswithactiveand inactiveparticlesembeddedinthematrix.Duetoinherentheterogeneities,thesecathodes generate mechanicalstressessufficientenoughtocausetheinitiationandpropagationof numerous typesoffractures.Inparticular,theemergenceofinter-andintra-granularcracks as wellasparticle-matrixinterfacedebondinghindersthetransportoflithium-ionsandelectrons, resulting incapacityfading.Therefore,addressingthemechanicaldegradationofcathode along withgeometricalconfigurationandmicro-structuralfeaturesisofmajorconcerntowards achievingenhancedandsustainableelectrochemicalperformance.Consequently,wehave developedathermodynamicallyconsistentmulti-physicsframeworktounderstandthechemo- mechanical interplaytowardsfracturebehaviorofpolycrystallinemicrostructurealongwiththe substrate/matrix. Theproposedframeworkaccountsfortheplasticdeformationofthehost lattice andthesubstrate.Achemo-mechanicalcohesivezonemodel(CZM)isformulatedto simultaneously capturethedecohesionandtransportacrossgrainboundaries,whileclassical CZM isusedbetweenthecathode/substrateinterface.Usingthefiniteelementbasednumerical framework,weexaminethemechanicalfailureandattendantvoltageprofilesforvariousmicro- structural andelectrochemicalparameters(i.e.,grainsizeandchargerate). Moreover,theproposednumericalmodelisextendedtounderstandtheroleofinter-and intra-granular fractureonthecoupledchemo-mechanicalbehaviorofpolycrystallinecathode. In thatcontext,thermodynamicsbasedcoupledchemo-mechanicalmodelisdevelopedto investigatetheevolutionofcomplexcrackpropagationandemergentvoltageprofilesfor polycrystalline cathodeparticleembeddedinthematrix.Aregularphase-fieldfractureparameter is introducedtocapturetheinter-andintra-granularcrackpropagationtogetherwiththeparticle- matrix interfacedebondingintheelectrode;thereby,thecoupledgoverningequationsarederived. Twodiffusedinterfacephase-fielddescriptorsareutilizedtodescribethegrainboundariesand particle-matrix interfaces.Subsequently,thedifferentfractureenergiesofthegrains,grain boundaries andparticle-matrixinterfacesareincorporated.Usingthefiniteelementbased numerical framework,theinteractionsbetweenthechemo-mechanicalbehaviorandattendant fracture mechanismsareaddressedtowardstheemergentelectrochemicalresponses.Various parametric studiesareperformedtoinvestigatetheeffectofgrainsizes,chargerates,and elastic modulusofthematrixontheoccurrenceofmultiplefracturemechanismswithinthe polycrystalline cathode.