Ultra-thin holey-reduced graphene oxide/Ni(picolinic acid)2 papers for flexible battery-supercapacitor hybrid devices

Abstract Metal-organic frameworks have attracted great interest as a kind of promising electrode materials for electrochemical energy storage, due to their porous skeleton in favor of electrolyte ion diffusion for reversible redox reactions of metal ions, but usually suffer from poor conductivity and low packing density, to the disadvantage of boosting rate capability and volumetric capacitance. We report a novel flexible battery-supercapacitor hybrid (BSH) device based on the holey-reduced graphene oxide (HRGO) anode and the HRGO/Ni(picolinic acid)2 (Ni(PA)2) cathode. The HRGO obtained by etching RGO with nitric acid through hydrothermal process, exhibits abundant micropores in favor of fast electrolyte ion diffusion. The ultra-thin stratiform HRGO/Ni(PA)2 paper prepared through the adsorption of Ni2+ complex on HRGO and the hydrothermal process of HRGO/Ni2+ complex, can provide gravimetric and volumetric capacitances of 738 F g-1 at 1 A g-1 and 747 F cm-3 at 1 A cm-3. The assembled flexible BSH device can deliver the volumetric capacitance of 67.1 F cm-3 (at 0.79 A cm-3), rate capability of 80% (from 0.79 A cm-3 to 7.9 A cm-3), energy density of 23.7 Wh L-1 (at 632 W L-1), cycling stability of 83.3% (after 10000 cycles), opening up new avenues for developing high-volumetric flexible energy storage devices.