(Invited) Interfacial Stability and Conductivity of Solid Electrolytes: Insights Gained from in Situ and Functional Electron Microscopy

In spite of different chemistries, many novel battery configurations, e.g., Li- air, Li-S, aqueous, and all-solid-state Li batteries, etc., share the same concept of using solid electrolyte materials to enable the use of lithium metal. An ideal solid electrolyte material must be highly ionically conductive and exhibit desirable stabilitywith metallic lithium. Over the past several decades, new solid electrolyte materials were developed that demonstrated high conductivity. However, the interfaces, including both internal grain boundaries within solid electrolytes and external interfaces between solid electrolytes and electrode, often show unexpected resistivity, degraded cyclability and vulnerability to dendrite propagation, presenting the current major limitations in realizing the practical application of solid electrolytes. Understanding what is happening at these interfaces at sufficient spatial, temporal and chemical resolutions are critical but challenging, due to spatial confinement and structural complications. Our research focuses on utilizing and developing advanced in situ and functional scanning transmission electron microscopy (STEM) to elucidate fundamental issues that lead to limited performance of interfaces in solid electrolytes, and to provide insights into the design and the engineering of high-performance interfaces. In this presentation, I will give several examples to demonstrate some of our recent studies in (i) elucidating the preferred dendrite-propagation at grain boundaries in the garnet-structured Al-Li7La3Zr2O12(LLZO); (ii) evaluating ion mobilities of H+and Li+ions individually in LLZO critical to its applications as a protection layer in aqueous batteries; and (iii) understanding the interfacial resistivity of LIPON with Li metal anode. Our results not only provide valuable insights into the understanding and the design of interfaces in Li-metal batteries, but also offer unique characterization methods that are generally applicable into the fundamental studies of solid-solid interfaces that involve mobile charge species and/or extremely chemically-active metallic lithium. Acknowledgement Research sponsored by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy. Microscopy performed as part of a user project at Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences (CNMS), which is a U.S. DOE User Facility.