Portable and foldable electronic devices had been shown to be highly desired in the current life and further dominate the future life.[1–4] To this end, it becomes critically important to develop matchable energy storage systems such as electric double-layer capacitors (EDLCs) to power them. The EDLCs should be lightweight, flexible and stretchable, and could be easily integrated with high performances.[5–8] However, the available EDLCs typically appeared in a heavy and rigid plate which could not meet the above requirements.[9–11] Recently, some attempts were made to explore lightweight and flexible EDLCs in a wire format by twisting two fiber electrodes together.[12, 13] Compared with the conventional planar structure, the wire-shaped EDLC could be woven into electronic clothes by the well-developed textile technology and show promising applications in a wide variety of fields. However, the high contact resistance between two twisted fiber electrodes has largely decreased the energy storage capability. In addition, they are not stretchable in the straight wire state, so the resulting electronic textiles based on the wire-shaped EDLC will break during the use.

Due to the remarkable mechanical, electrical, and thermal properties, carbon nanotubes (CNTs) have been widely studied as electrode materials to fabricate EDLCs.[14–16] CNTs could be used either as a conductive agent or for an electrode material. In addition, all CNT-based capacitors have been also realized mainly on the basis of liquid electrolytes such as aqueous KOH or H2so 4 solution and organic acetonitrile solution, although both of them exhibited relatively low specific capacitances, eg, 10 F cm− 3 and 20–40 F g− 1 (with energy density of 69.4 Wh kg− 1 and power density of 43.3 kW kg− 1), respectively.[17–19] In addition, complex fabrication processes are required to seal such capacitors with liquid electrolytes. To this end, several attempts