3D Imaging of Lithium Protrusions in Solid-State Lithium Batteries using X-Ray Computed Tomography

Solid-state lithium batteries will revolutionize the lithium-ion battery and energy storage applications if certain key challenges can be resolved. The formation of lithium-protrusions (dendrites) that can cause catastrophic short-circuiting is one of the main obstacles, and progresses by a mechanism that is not yet fully understood. By utilizing X-ray computed tomography with nanoscale resolution, the 3D morphology of lithium protrusions inside short-circuited solid electrolytes has been obtained for the first time. Distinguishable from adjacent voids, lithium protrusions partially filled cracks that tended to propagate intergranularly through the solid electrolyte, forming a large waved plane in the shape of the grain boundaries. Occasionally, the lithium protrusions bifurcate into flat planes in a transgranular mode. Within the cracks themselves, lithium protrusions are preferentially located in regions of relatively low curvature. The crack volume filled with lithium in two samples is 82.0% and 83.1%, even though they have distinctly different relative densities. Pre-existing pores in the solid electrolyte, as a consequence of fabrication, can also be part-filled with lithium, but do not have a significant influence on the crack path. The crack/lithium-protrusion behavior qualitatively supports a model of propagation combining electrochemical and mechanical effects.