Impacts of Microstructures on the Ionic Diffusivity of Solid Electrolytes: Mesoscale Modeling Approach

Abstract

Development of viable solid electrolytes is key for commercial adoption of all-solid-state batteries that can solve critical issues associated with electrochemical stability and safety for wider scale applications of the current battery technology. Recent years have seen the emergence of several solid electrolyte candidates with high ionic conductivity; however, practical processing and synthesis routes often generate internal interfaces that can disrupt conduction channels in these materials. In this talk, we will present our development of an efficient mesoscopic computational method for predicting the effective diffusivity through a solid electrolyte with a complex polycrystalline or polygranular microstructure. Our method considers simultaneous interfacial and bulk conduction modes, going far beyond simplified circuit descriptions to account for factors such as orientational variation of crystallite domains and the effects of interfacial strain. Using the Li7La3Zr2O12 (LLZO) solid electrolyte as a model system, we show how our simulation framework can be parameterized using a multiscale approach that derives digital microstructures from phase-field simulations and diffusivity tensors of reference phases and boundaries from molecular dynamics simulations. Simulations of the effective diffusivity of polycrystalline LLZO are applied to investigate the relationship between relevant microstructural features and ionic conductivity, with a focus on topological features of grains and grain networks. Using several instances, we will discuss a high sensitivity to these features, highlighting the need to account for microstructure when assessing mass transport in LLZO and related solid electrolyte materials. This work of was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.