3D self-supported hierarchical lettuce-like Ni3S2 super architecture with an internal nanowire network for high-performance supercapacitors

Tremendous efforts are devoted to the rational design of self-supported hierarchical architectures that are capable of delivering ultrahigh areal capacitance, and that are essential for miniaturized energy storage devices. Herein we propose a one-step-solvothermal approach for the hierarchical advancement in the morphology of the Ni ₃S ₂ on Ni foam from one-dimensional (1D) nanowires to a three-dimensional lettuce-like architecture with an internal nanowire network and corals at the edges. As the formation of this unique 3D lettuce-like architecture has resulted from the integration of 2D sheets with internal 1D nanowires, the combined features make it possible to realize ultra-high capacitance. This 3D architecture Ni ₃S ₂ electrode efficiently offers ultrahigh areal capacitance of 14.64 F cm ⁻², five times higher than that of nanowire arrays of 2.82 F cm ⁻² at the higher current density of 10 mA cm ⁻². A high value of 5.90 F cm ⁻² achieved, even at a larger current density of 50 mA cm ⁻², and retention of about 93% of the original capacitance over 7500 charge–discharge cycles when the applied current density is 150 mA cm ⁻² , makes it a potential electrode material for large-scale energy storage devices with confined areas, like micro-supercapacitors. In addition, an as-fabricated asymmetric supercapacitor (ASC) exhibits areal capacitance of 597 mF cm ⁻² , an energy density of 0.21 mWh cm ⁻², and a power density of 4.44 mW cm ⁻² at 10 mA cm ⁻², with high rate capability and capacitance retention of 79.5% over 10,000 cycles.