Flexible all-solid-state hierarchical NiCo2O4/porous graphene paper asymmetric supercapacitors with an exceptional combination of electrochemical properties

Two nanostructured electrodes were fabricated and used to construct flexible high performance supercapacitors. Hierarchical NiCo2O4 nanostructures (with airy organdy NiCo2O4 nanosheets on vertical NiCozai nanoarrays) were grown on flexible carbon cloth by a facile template-free method while three dimensional (3D) porous graphene papers (PGP) with scaffold-like microstructure were fabricated by freeze-drying. The hierarchical NiCo2O4/carbon cloth (NiCo7O4/CC) and PGP electrodes achieved the maximum specific capacitance of 1768 (based on the mass of NiCo2O4) and 151 F g(-1), respectively. The NiCo2O4/CC (as the positive electrode), PGP (as the negative electrode), and PVA-LiOH gel (as both the solid state electrolyte and separator) were assembled into flexible all-solid-state (NiCo2O4/CC//PGP) asymmetric supercapacitor with an exceptional combination of electrochemical properties in terms of working potential (1.8 V), maxmum energy density (60.9 W h kg(-1)), maxmium power density (11.36 kW kg(-1)), and cycling stability (96.8% capacitance retention ratio over 5000 cycles under mechanical bending). (C) 2015 Elsevier Ltd. All rights reserved.