In the freshly deposited case, where we immediately disassembled the cells after lithium deposition and the half-stripped case, where we stripped the lithium metal anode halfway, we found that no obvious intraparticle heterogeneity had developed inside the dendrites (Fig. , Supplementary Movie 3). On the contrary, we observed lithium dendrites with non-uniform contrast in the main body in the case of calendar aging for 24 hours after initial lithium deposition (Fig. ). The heterogeneity consistently appeared darker throughout the tilt series (Supplementary Movie 4) and arose from a difference in the scattering materials in this region. To isolate and analyze this intraparticle heterogeneity, we leveraged convolutional neural networks to do image segmentation and automatically identify the heterogeneity region in the reconstructed tomograms (Fig. ).