LIBs), stretchable supercapacitors, and stretchable silver-zinc batteries. [5][6][7][8] Most of them mainly focused on the development of deformable current collectors (e.g., embedding conductive materials in soft substrates or elastic substrates) [9,10] or structural layouts (e.g., helically coiled spring design, serpentine interconnected configuration, and origami structure). [11][12][13] In comparison, a stretchable separator membrane for deformable energystorage devices attracts little attention. The separator membrane is basically used to prevent physical and electrical contact between electrodes while offering an ion conduction channel. [14] Various types of stretchable batteries are being developed, and thus the stretchable properties of the separator membrane are also required. Generally, because ionic gel-polymer electrolytes (GPEs) are easily controllable and sufficiently deformable, they have been employed as the separator membrane in deformable energy-storage devices. [13,15,16] Although ion-conducting GPEs can be used as both electrolyte and separator, they have intrinsically lower ionic conductivity than liquid electrolytes [17] and poor mechanical properties which are likely to cause an internal short problem due to the contact of both electrodes under physical deformation. [18,19] In order to fabricate a reliable stretchable energy-storage device without these limitations, the presence of a physical separation barrier having an ion-conducting channel and stretchability is essential. Recently, Liu et al. reported a stretchable separator membrane for wavy-structured stretchable LIBs using electrospinning techniques. [20] Li et al. also used electrospinning process to fabricate a stretchable polyurethane separator for stretchable supercapacitor. [21] However, electrospinning has critical drawbacks such as the use of complex equipment, slow production rate, and possible toxicity of chemical residues in electrospun fibers. Moreover, it has the limitation for largescale production for industry level due to its high cost. [22,23] Given these limitations, it is still necessary to develop and improve the fabrication methodologies for stretchable separator membranes. Although various attempts have been made in the membrane component to achieve the complete stretchability of the battery, the development of the standardized separator membrane that can be applied to various types of stretchable battery has not yet been reported. Therefore, the development of stretchable separator membranes with high processibility With the emergence of stretchable electronic devices, there is growing interest in the development of deformable power accessories that can power them. To date, various approaches have been reported for replacing rigid components of typical batteries with elastic materials. Little attention, however, has been paid to stretchable separator membranes that can not only prevent internal short circuit but also provide an ionic conducting pathway between electrodes under extreme physical deformation. Herei...