High-throughput dynamic modeling of Li migration behaviors in garnet electrolyte

Abstract

Showering electrons into Li6.4La3Zr1.4Ta0.6O12 (LLZTO) can create a finite surface charging layer to drive the expulsion of metal lithium out the garnet electrolyte, thanks to high ionic conductivity, low electron conductivity and good thermochemical stability of the ceramic electrolyte. Tantalum distribution within the microstructure may control the lithium migration behaviors, which affects lithium dendrite formation through all-solid-state lithium-ion batteries. In this study, we employ a high-throughput lithium expulsion experiment in a scanning electron microscope to model the Li+ migration behaviors within the garnet microstructure. Ta-rich and Ta-poor zones were found to co-exist within the matrix of LLZTO grains, which was densified by a two-step reactive sintering. By associating the modeling parameters of the parallel lithium expulsion events with their local ionic conductivity, three types of lithium migration processes were categorized and their correlations with the inhomogeneous garnet phase could be revealed. Such dynamic modeling reveals not only the origin of variable conductivity, but also those intra-granular boundaries as easier migration paths and accumulation sites for Li+ than the grain boundaries. Charging and subsequent expulsion turn the garnet surface as an anode in a half-battery, even when the driving electric field varies with the changing conductivity of lithium in the electrolyte.