Solid-state batteries have seen a dramatic increase in research in recent years because of their ability to address safety challenges associated with flammable liquid electrolytes, and the potential to enable Li metal anodes. However, the formation of solid-solid interfaces poses unique challenges compared to solid-liquid interfaces. This requires new methods to study the fundamental behavior of solid-solid interfaces, and understand their dynamic evolution during cycling.
In this talk, I will present a suite of multi-modal in situ/operando characterization approaches that we have used to study Li metal-solid electrolyte interfaces during cycling. First, to gain an improved understanding of the electrochemical stability, I will discuss operando X-ray photoelectron spectroscopy (XPS) analysis of lithium metal-solid electrolyte interfaces. This approach allows us to directly observe interphase formation and evolution as the electrochemical potential of the solid-electrolyte surface is biased to potentials below the thermodynamic potential for Li plating. A range of sulfide and oxide ceramic electrolytes were explored, since they exhibit a range of (in)stability levels during Li metal plating.
To compliment these spectroscopic measurements, in situ/operando microscopy techniques will also be presented. Operando optical microscopy allows for direct observation of the nucleation and growth of Li filaments both into, and out of, solid electrolyte surfaces. By time synchronizing the optical video analysis with the electrochemical signatures of plating and stripping, new insights into the dynamic evolution of morphology and associated electrochemical analysis can be obtained. Furthermore, I will contrast the mechanisms that limit rate capability in the anode and cathode, by illustrating the critical role of microstructure in composite cathodes for SSBs. By integrating the observations across this multi-modal characterization approach, the implications for SSB performance and stability will be discussed, and critical needs for future research will be described.