Three-dimensional (3D) conductive scaffolds have attracted intensive interest recently for Li metal anode due to the capability of suppressing Li-dendrite growth. However, there is a lack of comprehensive understanding of its multiple roles including any side effects, which is critical for lithium metal anode technology. Here, we fabricate a type of Au-coated polyimide nanofabric as the scaffold for Li-metal anode and study the lithium plating/stripping behavior with different current densities. Different from reported studies which usually only discussed the benefits of 3D scaffolds, this study reveals unstabilized solid-electrolyte-interphase (SEI) with 3D architectures. It is found that 3D scaffold tends to form unstable SEI layer at high current density, which finally results in a short cell life due to continuous SEI accumulation and fast consuming of liquid electrolyte. To better understand this new finding, we propose an electrochemomechanical failure model for lithium metal anode, which will be instructive for designing advanced structures to electrochemomechanically stabilize Li-metal composite anode. Published by Elsevier Ltd.