We demonstrate the fabrication of high-integrity flexible supercapacitors using carbon nanotubes (CNTs), polyethylene terephthalate (PET) films, and ion gels. Although both CNTs and PET films are attractive materials for flexible electronics, they have poor adhesion properties. In this work, we significantly improve interfacial adhesion by introducing nanostructures at the interface of the CNT and PET layers. Simple reactive ion etching (RIE) of the PET substrates generates nano-scale roughness on the PET surface. RIE also induces hydrophilicity on the PET surface, which further enhances adhesive strength. The improved adhesion enables high integrity and excellent flexibility of the fabricated supercapacitors, demonstrated over hundreds of bending cycles. Furthermore, the supercapacitors show good cyclability with specific capacitance retention of 87.5% after 10,000 galvanostatic charge-discharge (GCD) cycles. Our demonstration may be important for understanding interfacial adhesion properties in nanoscale and for producing flexible, high-integrity, high-performance energy storage systems. (C) 2015 Elsevier B.V. All rights reserved.