<p>Despite
progress in solid-state battery engineering, our understanding of the
chemo-mechanical phenomena that govern electrochemical behavior and stability
at solid-solid interfaces remains limited compared to solid-liquid interfaces.
Here, we use <i>operando</i> synchrotron X-ray computed microtomography to
investigate the evolution of lithium/solid-state electrolyte interfaces during
battery cycling, revealing how the complex interplay between void formation,
interphase growth, and volumetric changes determines cell behavior. Void
formation during lithium stripping is directly visualized in symmetric cells,
and the loss of contact at the interface between lithium and the solid-state
electrolyte (Li<sub>10</sub>SnP<sub>2</sub>S<sub>12</sub>) is found to be the
primary cause of cell failure. Reductive interphase formation within the
solid-state electrolyte is simultaneously observed, and image segmentation reveals
that the interphase is redox-active upon charge. At the cell level, we
postulate that global volume changes and loss of stack pressure occur due to
partial molar volume mismatches at either electrode. These results provide new
insight into how chemo-mechanical phenomena can impact cell performance, which
is necessary to understand for the development of solid-state batteries.</p>
Linking Void and Interphase Evolution to Electrochemistry in Solid-State Batteries Using Operando X-Ray Tomography