In Situ and Operando XPS and Related Measurement Approaches for Interfacial Studies of Solid-Electrolyte Materials for Battery Applications

In recent years there has been growing interest around <i>in situ</i> and <i>operando</i> approaches for studying interfacial phenomena, including charge- and mass-transfer processes relevant to solid-electrolyte systems and battery technologies in general. Laboratory-based X-ray photoelectron spectroscopy (XPS) and scanning Auger microscopy (SAM) are powerful techniques for analyzing surfaces and interfaces to reveal compositions and chemical states, including depth profiling and 2D mapping experiments. This presentation will discuss recent efforts by researchers at the National Renewable Energy Laboratory (NREL) to apply <i>in situ</i> and <i>operando</i> approaches to probe interfacial charge transfer and phase transformations relevant to the formation and evolution of the solid-electrolyte interphase (SEI) on novel solid-electrolyte materials. These experiments are enabled by the virtual electrode (VE) approach, in which electrochemical currents are driven during VE-XPS measurements on exposed interfaces via a combination of low-energy Li⁺ ion and electron guns and ultraviolet-based photoemission.