Lithium metal deposition was carried out in a commercial carbonate electrolyte, 1M LiPF6 in ethylene carbonate (EC)/diethylene carbonate (DEC). Freshly deposited Li metal, half-stripped Li metal, and calendar aged Li metal samples were prepared. The cryo-EM sample preparation and transfer procedures followed the previous report and details can be found in the Methods section. To obtain a tomogram of the object of interest in cryo-ET, a series of projection images was taken between ±60 o at an angular increment of 1 o under a dose-symmetric scheme. The projection image series will then be pre-processed and aligned to be ready for tomogram reconstruction. The computational reconstruction can be carried out with the available algorithms, for example the weighted back-projection method (Fig. ). Of note, for tomography, it is preferred that the Li metal dendrites sit in the same direction as the tilting axis of the microscope to maximize the spatial information of the tomograms. Thus, we chose not to grow Li dendrites directly onto the bare Cu grid, as this would make it difficult to obtain Li dendrites that had the same orientation as the tilt axis.