High‐Mass‐Loading CoNi‐Layered Double Hydroxide Directly Grown on Brush‐like Cu/Carbon Cloth as High‐Areal‐Capacitance Supercapacitor Electrode

Abstract A combination of high mass loading and efficient utilization of electroactive materials is crucial for simultaneously enhancing the energy and power densities of energy storage devices. This is exemplified herein using cobalt nickel layered double hydroxides nanosheets (CoNi‐LDHs) directly grown on copper nanowires (Cu NWs) standing quasi‐vertically on carbon cloth (CC) to yield a multi‐core‐shell CoNi‐LDHs/Cu NWs/CC as the supercapacitor electrode that exhibits a high areal capacitance of 5.55 F cm−2 (corresponding to a gravimetric capacitance of 1209.15 F g−1) at a large current density of 10 mA cm−2. Such superior rate capability is attributed to the high packing density of CoNi‐LDHs in the electrode, benefitting from the large specific surface area of Cu NWs/CC. Additional contribution stems, on the other hand, from the facile charge transfer kinetics resulted from the elimination of binder from the electrode coupled with the mesopores between not only Cu NWs but also CoNi‐LDHs nanosheets, and the macropores between the carbon fiber of CC. Benefitting from such exceptional rate performance is the supercapacitor built on CoNi‐LDHs/Cu NWs/CC as the positive electrode coupled with bismuth subcarbonate (Bi2O2CO3) as the negative electrode capable of delivering outstanding power density of 13.31 mW cm−2 and energy density of 0.35 mWh cm−2.