Holey nickel-cobalt layered double hydroxide thin sheets with ultrahigh areal capacitance

Strong coupling of electroactive components on conductive carbonaceous matrix to fabricate flexible hybrid electrodes represents a promising approach towards high performance supercapacitors. This work reports the fabrication of holey nickel cobalt layered double hydroxide (NiCo-LDH) nanosheets that are vertically grown on the cotton cloth-derived activated textile carbon (aTC). The abundant nanoholes on the thin-sheet NiCo-LDH not only enhance the electrode efficiency for efficient Faradaic redox reactions but also facilitate access of electrolyte to the electrode surface, thus giving rise to 70% capacitance arising from their outer surface. As a result, the aTC-NiCo hybrid electrode is capable of simultaneously achieving extremely high areal capacitance (6.37 F cm−2), mass capacitance (525 F g−1) and volumetric capacitance (249 F cm−3) at a practical level of mass loading (6.72 mg cm−2). Moreover, a solid-state asymmetric capacitor built with aTC-NiCo as positive electrode and active carbon-coated on aTC as negative electrode can deliver a volumetric energy density of 7.4 mWh cm−3 at a power density of 103 mW cm−3, while preserving a superior power performance, satisfying cycling stability and good mechanical flexibility.