Solid electrolytes for solid-state and lithium-sulfur batteries

Abstract

The stringent demands placed on batteries by emerging vehicle technologies such as plug-in and battery electric vehicles suggest that improvements in the safety and performance of electrochemical energy storage devices, as well as concurrent reductions in their cost, are highly desirable. Current strategies for improving performance have largely focused on Li-ion battery chemistries. In this project went beyond the state of the art by pursuing electrolyte chemistries that will enable the use of Li metal anodes and sulfur cathodes, either concurrently in a solid state Li-S battery, or as a means to achieve a Li metal anode which is stable upon cycling. More specifically, our effort advanced strategies to enable Li metal anodes for myriad beyond Li-ion chemistries . LLZO garnet (Li 7 La 3 Zr 2 O 12 ) is the first bulk-scale ceramic electrolyte to exhibit the combination of superionic conductivity (1mS/cm at 298K), high shear modulus (61 GPa) to suppress Li dendrite penetration, and apparent electrochemical stability (0-6V vs Li/Li + ), thus enabling Li metal anodes. However, to date there are no reports confirming LLZO can tolerate current densities > 1mA/cm 2 , thus demonstrating relevance to PHEV/EV batteries. Our goal was to investigate the mechanisms that govern the Li-LLZO interfacial stability as a function of current density. We determined that defects in polycrystalline LLZO reduce the critical current density (CCD). Primarily contaminants on the LLZO surface and grain boundaries were the primary defects the limited the CCD. Using our experience with synthesis and processing (Sakamoto and Wolfenstine) and sophisticated materials characterization (Nanda), we precisely controlled atomistic and microstructural defects and correlated their effects on controlling the critical current density. These data fed into multi-scale computation models (Siegel and Monroe) to isolate and quantify the roles that each defect played in controlling the critical current density. Bridging this knowledge gap allowed us to demonstrate that LLZO can withstand > 1mA/cm 2 .