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 NiCo₂O₄ 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 (NiCo₂O₄/CC) and PGP electrodes achieved the maximum specific capacitance of 1768 (based on the mass of NiCo₂O₄) and 151Fg^-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 (1.8V), maxmum energy density (60.9Whkg^-1), maxmium power density (11.36kWkg^-1), and cycling stability (96.8% capacitance retention ratio over 5000 cycles under mechanical bending).