Facile synthesis of 3D/2D Cu2Se cauliflower/CuS nanosheets composite as a binder-free electrode for high-performance asymmetric solid-state supercapacitors

In this work, we demonstrate a facile, binder-free technique to fabricate 3D Cu2Se nano-cauliflower with 2D CuS nanosheets as a composite on Ni foam by co-electrodeposition technique for high-performance solid-state supercapacitor. The morphology of the composite (Cu2Se@CuS) was confirmed by the scanning electron microscope and the crystal phases of monoclinic Cu2Se and hexagonal CuS were obtained using X-ray diffraction technique. The Cu2Se@CuS composite delivered an ultra-high specific capacitance of 2727 F g−1, compared to its single compound material Cu2Se (1925 F g−1) and CuS (1156 F g−1), respectively at current density of 2.5 mA cm−2 in three-electrode configuration. Ni foam, as a binder-free conducting substrate, acts as uniform growth point for electrode materials and accelerates the transportation of ions throughout the electrode while the synergistic effect of Cu2Se and CuS and their efficient redox properties contribute to faster diffusion path for both electrolyte ions and electrons. Moreover, the assembled asymmetric solid-state supercapacitor Cu2Se@CuS// AC with PVA-KOH gel as supporting electrolyte delivered an excellent specific energy of 42.7 Wh Kg−1 (1.95 Wh cm−3) at specific power of 381 W kg−1 (17.55 W cm−3). The solid-state device achieved a good cyclic stability of 70.2% capacitance retention even after 8000 cycles. This technique of a simple co-electrodeposition method outlined in this work to engineer 3D/2D nanostructured electrode provides a potential strategy for fabricating high performance, free-standing energy storage devices.