Multi-scale microscopy of the Li/electrolyte interface in solid-state next-generation batteries

Abstract

The transition to renewable energy sources is dependent on the availability of sufficient storage. To meet these urgent demands, scientists are racing to find new battery chemistries and architectures One of the promising next-generation technologies is all-solid lithium (Li) batteries, which utilizes ion-conducting solids such as β-Li3PS4 (LPS) ceramic in place of conventional organic liquid electrolytes. This enables use of a Li metal anode which increases theoretical capacity, improves battery safety by replacing flammable liquid electrolytes, and in some cases widens the stable voltage window over traditional Li-ion electrolytes. However, Li anodes in solid-state systems experience undesired Li migration which can result in short-circuit and premature battery death. The core focus of my research is to use imaging techniques to detail the fundamental electrochemical processes governing the Li migration in ceramic solid electrolytes, using LPS as a model system. To achieve comprehensive understanding, it is necessary to characterize the Li/electrolyte interface at all relevant scales, which is only possible by using a collection of different techniques. In my work I used scanning electron microscopy (SEM) paired with Li sensitive energy dispersive spectroscopy (EDS) as well as two X-ray imaging techniques: synchrotron computed tomography (CT) and transmission X-ray microscopy (TXM). This presentation will first highlight the results of operando synchrotron CT studies, collecting 3D X-ray images of the Li/LPS interface while the battery is cycling, supported with complementary SEM studies with Li-sensitive EDS. The development of this operando synchrotron CT technique to control and manipulate variables that are relevant in realistic solid-state batteries will be described along with major results that show interaction between the Li metal and pre-existing defects in the LPS electrolyte and reveal that multiple mechanisms of Li migration may be dominant depending on cell operating conditions. Next, methodologies that advance TXM, a nano-scale X-ray imaging technique, toward the operando capabilities necessary for detailed investigation of mechanisms at nanoscale will be covered, including detailed discussion of challenges associated with sample preparation and fabrication of the cells with appropriate dimensions, TXM experiments, and data analysis. The outcome of this work is a multi-scale morphological characterization, ranging from the nano-scale to micro-scale to the whole device, contributing to mechanistic understandings of fundamental science related to battery degradation and development of novel capabilities that could be applied to wider range of systems.