Sandwich-like NiCo layered double hydroxide/reduced graphene oxide nanocomposite cathodes for high energy density asymmetric supercapacitors

Nanocomposites with a well-defined sandwich-like nanostructure were prepared via in situ growing NiCo-layered double hydroxide nanosheets with tunable Ni/Co ratios on reduced graphene oxide (rGO). Electrochemical impedance spectra and N-2 adsorption/desorption isotherms confirmed that these sandwich nanostructures effectively promoted charge transport and enlarged the specific surface area. The nanocomposites with Ni:Co = 2:1 exhibited a maximum specific capacitance of 2130 F g(-1) at 2 A g(-1), excellent rate capability (72.7% retention at 15 A g(-1)), and cycling stability. Asymmetric supercapacitors were assembled with these nanocomposite cathodes and rGO as a negative electrode (anode), and demonstrated an energy density of 34.5 W h kg(-1) at a power density of 772 W kg(-1), while maintaining a capacity retention of 86.7% after 10000 cycles at 5 A g(-1). The robust electrochemical properties indicate the composites as promising electrodes for electrochemical energy storage devices.