Li metal experiences significant morphological changes during operation, resulting in rapid electrochemical performance degradation. In this study, a traditional balloon trick is applied to the Li metal surface to release mechanical stress and hinder morphological changes during operation. Polymer separators directly attach to the Li metal surface using a polymeric adhesive to fabricate a separator/Li metal integrated assembly. The separator/Li metal assembly improves not only the electrochemical performance but also safety issues related to Li metal anodes. This approach has three main advantages: (i) Li metal surface stabilization. The separator/Li metal assembly mechanically stabilize the Li metal surface, resulting in improved rate capability and cycle performance [85.0% of initial discharge capacity (90.2 mAh g–1) at a 7C condition for rate capability and 87.6% of discharge capacity (95.5 mAh g–1) at the 220th cycle] compared with the bare Li metal without separator integration [82.6% of initial discharge capacity (84.5 mAh g–1) at a 3C condition for rate capability and 58.0% of discharge capacity (62.6 mAh g–1) at the 120th cycle]. (ii) Suitability for high energy density battery implementation. The thickness of the polymeric adhesive is less than 1 μm, which is one-tenth of the coating layer of conventional thermally stable separators, but exhibits similar thermal shrinkage characteristics (0% shrinkage at 140 °C for 30 min). By reducing the thickness of inactive components, a larger volume of active material can be loaded into the battery system to increase the energy density of the battery. (iii) Simple process for mass production. The separator/Li metal integration process (“stick” and “dry”) is very simple and can be easily applicable across industries.