Herein, we demonstrate for nanometer resolution imaging of 3D structure of freshly deposited and aged Li metal anode materials by leveraging the recent development of cryo-EM and cryo-ET, which leads to new findings. In calendar aging, two different phenomena were observed: the growth of LiH and the growth of extended SEI . In short term calendar aging, we only observed the growth of LiH in Li metal anodes. In longer term calendar aging, there was more extensive LiH and extended SEI growth, preferentially associated with the Li metal portion rather than LiH portion of the dendrite. While we cannot rule out other possibilities, the observation that the majority of extended SEI is on the Li metal portion in the dendrite indicates that the growth of extended SEI was largely localized to the Li metal surface.