Resolving Three-Dimensional Nanoscale Heterogeneities in Lithium Metal Batteries with Cryogenic Electron Tomography

Current direct observation of sensitive battery materials and interfaces primarily relies on two-dimensional (2D) imaging, leaving out their three-dimensional (3D) relationship. Here, we used cryogenic electron tomography (cryo-ET) to visualize the lithium metal anode in 3D at nanometer resolution and cryogenic electron microscopy (cryo-EM) to reveal atomic details in local regions. We imaged both freshly prepared and calendar aged Li metal anodes to reveal the development of LiH in Li dendrites and the Li-LiH interface, as well as the development of the solid-electrolyte interphase (SEI). Using a convolutional neural network-based technique, the 3D arrangement of Li metal, along with nanoscale LiH and Cu heterogeneities in dendrites were visualized and annotated. In longer-term calendar aging, we observed more substantial LiH growth accompanied by extended SEI growth. Our results show that the growth of LiH and of the extended SEI during battery calendar aging are temporally and spatially separate processes