The Role of Local Inhomogeneities on Dendrite Growth in LLZO-Based Solid Electrolytes

Pallab Barai,Kenneth Higa,Badri Narayanan,Larry A. Curtiss,Venkat Srinivasan,Anh T. Ngo

doi:10.1149/1945-7111/ab9b08

Abstract

The majority of the ceramic solid electrolytes (LLZO, LATP) demonstrate polycrystalline grain/grain-boundary (G/GB) microstructure. Higher lithium (Li) concentration and lower mechanical stiffness result in current focusing at the GBs. Growth of Li dendrites through local inhomogeneities and subsequent short circuit of the cell is a major concern. Recent studies have revealed that bulk Li metal is a viscoplastic material that has low (∼0.3 MPa) and high (∼1.0 MPa) yield strength during deformation at smaller and larger rates of strain, respectively. It has been argued that during deposition at smaller current densities, due to its lower yield strength, Li metal should demonstrate plastic flow against stiff ceramic electrolytes, and Li dendrites will be prevented from penetrating through solid electrolytes. In this manuscript, a multiscale modeling framework has been developed for predicting properties of GBs and the bulk of ceramic electrolytes using atomistic calculations for input to mesoscale models. Using the parameters obtained from the atomistic simulations, the mesoscale model reveals that, given enough time, even at low charge rates, lithium dendrites can grow through the GBs of LLZO. The present multiscale model results also provide information regarding the dendrite growth velocity through LLZO.

Highlights

To cite this article: Pallab Barai et al 2020 J
For the first time, the authors demonstrated a multiscale model capable of capturing the growth of lithium dendrites through LLZO solid electrolytes. Several parameters, such as elastic modulus and Li conductivity within LLZO bulk grain interior and grain boundaries (GBs) region have been obtained from atomistic simulations
Plastic deformation of Li will delay the initiation of Li dendrites at the GB region.[26,27]

Summary

Introduction

To cite this article: Pallab Barai et al 2020 J. Examples of ceramic based SSEs are Li7La3Zr2O12 (LLZO), Li1.3Al0.3Ti1.7(PO4)[3] (LATP), Li10GeP2S12 (LGPS), and all of them demonstrate substantially different conductivities and mechanical properties at the grain boundaries (GBs) and the bulk (or grain interior) domain.[9,11,12,13] Here, we focus on the LLZO based ceramic SSE, because of its relatively high room temperature conductivity and enhanced chemical stability with respect to Li.[4,14] In order to stabilize the high conductivity cubic phase of LLZO, it is usually doped with aluminum (Al), or tantalum (Ta), or niobium (Nb), which helps to create vacancies and enhances the conduction of lithium ions.[14,15] Regarding the initiation of dendritic protrusions within LLZO based SSEs, multiple theories have been proposed that predict the propensity of dendrite formation either in the GB or inside the bulk grain interiors.[16,17] Density Functional Theory (DFT) based calculations estimate that excess electrons can be trapped around the lanthanum (La) atoms located near the surface of the cubic LLZO,[10] which has the capability to reduce lithium ions and form lithium precipitates inside the SSEs. Due to higher partial molar volume of lithium atoms than lithium ions,[18] such a precipitate can lead to the generation of substantial stress within the SSE, which can cause initiation of cracks.[19] Some other researchers have observed flow of electrons through the LLZO electrolyte,[20] and. Due to the lower melting temperature of Li (180 °C), at room temperature a metallic

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Conclusion