There is currently a great deal of interest in stretchable electronics for widespread applications such as wearable devices, smart sensors, healthcare devices, electronic skins, and soft robotics. The stretchable electronic devices that consist of soft and deformable components can stably maintain their functions under the complex physical deformations such as bending, twisting, folding, and stretching. To achieve independent and reliable stretchable electronics, a key challenge is the development of stretchable energy-storage devices that could power such devices. In this presenstation, I will present a functional separator membrane based on a non-induced phase separation method for achieving future advanced battery devices with high stretchability and high ionic conductivity for deformable batteries such as Lithium-ion battery and aqueous battery system.