All-solid-state Li-metal batteries aim for higher energy density and better safety than conventional Li-ion batteries due to their inflammable inorganic electrolytes and lithium metal electrode. The solid electrolytes are also believed to suppress Li-dendrite formation, which causes failure in organic liquid electrolytes. However, mechanical fracture and structural disintegration of the solid electrolytes can still occur during operation, leading to poor charge/discharge cyclic performance and increased likelihood of internal short circuits. Our research aims to understand how lithium metal penetration occurs. We will use neutron tomography, which is much more sensitive to lithium than X-ray tomography, to obtain the first observations of the progressive degradation of an all-solid-state Li-metal battery, by studying the spatial distribution of lithium.