Lithium metal batteries (LMBs) are considered the ideal choice for high volumetric energy density lithium-ion batteries, but uncontrolled lithium deposition poses a significant challenge to the stability of such devices. In this paper, we introduce a 2.5 μm-thick asymmetric and ultrastrong separator, which can induce tissue-like lithium deposits. The asymmetric separator, denoted by utPE@Cu₂O, was prepared by selective synthesis of Cu₂O nanoparticles on one of the outer surfaces of a nanofibrous (diameter ~10 nm) ultrastrong ultrahigh molecular weight polyethylene (UHMWPE) membrane. Microscopic analysis shows that the lithium deposits have tissue-like morphology, resulting in the symmetric lithium cells assembled using utPE@Cu₂O with symmetric Cu₂O coating exhibiting stable performance for over 2000 h of cycling. This work demonstrates the feasibility of a facile approach ultrathin separators for the deployment of lithium metal batteries, providing a pathway towards enhanced battery performance and safety.