All solid-state lithium batteries offer a necessary improvement to the safety of electric vehicles (EVs) in addition to the capacity improvements enabled by the use of lithium metal as an anode material. In order to accelerate the use of lithium metal anodes and solid electrolytes in consumer products, it is vital to understand the cycling behavior, electrode-electrolyte interfaces, and failure mechanisms of such systems. A promising class of solid electrolytes for achieving the use of all solid-state batteries in EVs is lithium-phosphorous-sulfides, which includes β-Li₃PS₄. This electrolyte has an ionic conductivity on the order of 10^-3 S cm^-1 and can be compressed to 80% density at room temperature.

This work probes the morphological evolution of the electrode-electrolyte interface and observes the growth of lithium dendrites in β-Li₃PS₄ using x-ray tomography, guided by thermography. Thermography enables the direct visualization of short circuits in the electrolyte, which are shown in Figure 1 to preferentially form in continuous boundary or void spaces, and identifies locations of interest to examine with x-ray tomography. With the density dependence of x-ray microscopy, it is possible to examine the correlation of lithium dendrite growth to voids or phase defects and to better understand the behavior of dendrites in high-modulus electrolyte systems. In order to better understand the reactions and mechanisms occurring during cycling as a function of current density, morphological changes detected with x-ray tomography are correlated with chemical information acquired using energy dispersive spectroscopy (EDS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Results will be presented for cold-pressed pellets of the conductive ceramic powder enclosed in lithium-lithium symmetric cells compared over three conditions: uncycled cells, cells cycled under low current, and cells cycled under high current, both for a specific amount of charge.