Lithium metal batteries (LMBs) are considered to be next-generation high-energy-density storage devices because of the ultrahigh theoretical specific capacity and low reduction potential of the Li metal anode. The electroplating/stripping behavior of Li metal and the properties of the solid-electrolyte interphase (SEI) are key issues that must be well understood. Traditional structural investigations using electron microscopy can facilitate this understanding, but they lack three-dimensional information. Herein, the burgeoning technique, cryogenic electron tomography, is used in the study of LMBs to visualize the morphology of electrochemically deposited Li metal and the SEI in various electrolytes. High-aspect-ratio dendrites are formed in ethylene carbonate-diethyl carbonate (EC-DEC) and EC-DEC/vinylene carbonate electrolytes, whereas irregularly shaped Li metal is formed in an EC-DEC-fluoroethylene carbonate electrolyte. In contrast, the use of a 1,3-dioxolane-1,2-dimethoxyethane-LiNO electrolyte produces spherical Li metal. Three-dimensional reconstructions of the Li dendrites formed after half-charging revealed polyhedral-shaped “dead Li” tightly wrapped by a folded SEI layer, indicating the mechanism of “dead Li” formation. The non-uniform stripping rate of Li and the elimination of electron conduction paths by the surrounding SEI husks lead to the formation of such “dead Li.”