Self-supported, additive-, and binder-free CuS nanowire array for high performing Na-ion capacitor

Na-ion capacitors are considered to be one of the most promising energy storage devices due to its low cost, safe, highly abundance in nature and comparable performance to lithium-ion capacitor. NICs provide high power density as well as good energy density in a single device. However, the lack of host materials to store Na-ions has challenged its commercialization. It is very important to investigate a suitable host material for the Na-ion capacitors. Metal chalcogenides shows significant electrochemical performance towards the NICs. The low capacitance value, stability in the electrolyte is the main drawbacks of the metal chalcogenides. The tailoring in the nanostructures and the component of the electrode can improve the electrochemical performance of Na-ion capacitors. Herein, a liquid-solid chemical method is developed to fabricate self-supported, binder, and additive-free CuS nanowires on porous copper foam electrode, and investigated for the first time as an anode for Na-ion capacitor. Using Cu-foam instead of Cu-foil as a substrate and current collector enhances the 5-fold capacitance (380 F g−1 at 1 A g−1) for Na-ion capacitors, which suggest the replacement of the Cu-foil as current collector. The involved conversion reaction in CuS NWs/Cu-foam is confirmed by in-situ XRD measurement. Since it is observed that the CuS NWs/Cu-foam exhibited good electrochemical and redox features with superior specific capacitance in three-electrode system, a symmetric device is assembled. The symmetric device shows 400 F g−1 of specific capacitance at 1 A g−1 with 28 Wh kg−1 of energy density and 1440 W kg−1 of power density. It is favourable that CuS nanowires are still preserving to the same morphology after 1000 charge-discharge cycles, which is confirmed by the SEM imaging.