Flexible, sandwich-like CNTs/NiCo2O4 hybrid paper electrodes for all-solid state supercapacitors

With the increasing demand for compact storage systems for portable and wearable electronic devices, flexible supercapacitors with high volumetric performance have attracted considerable attention. Here, we report a simple method to fabricate a sandwich-like carbon nanotubes (CNTs)/NiCo2O4 hybrid paper electrode, consisting of a layer of conductive CNT buckypaper coated with honeycomb-like NiCo2O4 nanosheets at both sides. Owing to the high conductivity of the CNT skeleton and vertically aligned structure of NiCo2O4 nanosheets, the free-standing hybrid paper possesses an ultra-high specific capacitance of 1752.3 F g(-1) and excellent cycling performance. A flexible all-solid-state symmetrical supercapacitor has been further assembled based on the hybrid paper. The device exhibits excellent volumetric energy and power densities (1.17 mW h cm(-3) and 2430 mW cm(-3)) and deformability, even under bending at an angle of 180 degrees. The hybrid paper can serve as a freestanding and flexible electrode for various energy devices.