Asymmetrical supercapacitor composed of thin Co(OH)₂ nanoflakes on three-dimensional Ni/Si microchannel plates with superior electrochemical performance

Nanoscale cobalt hydroxide (Co(OH)₂) particles are fabricated by electrodeposition on three-dimensional nickel/silicon microchannel plates (Ni/Si-MCPs) as the active electrode materials on the surface and sidewall of the Ni/Si-MCPs for miniature supercapacitors. The relationship among the electrodeposition time, morphology, formation mechanism of Co(OH)₂ nanostructure, and capacitor performance is studied. Using an optimal electrodeposition time of 6 min, the Co(OH)₂ supercapacitor has a capacitance of 697.56 F g^-1 (5.72 F cm^-2) at 2 mA cm^-2 and the retention ratio is 91.20% after 2500 cycles. The large areal capacitance and excellent rate capability can be attributed to the unique 3D ordered porous architecture which facilitates electron and ion transport, enlarges the liquid-solid interfacial area, and enhances the utilization efficiency of the active materials. Meanwhile, the weight and size of the device are reduced. By using the Co(OH)₂/Ni/Si-MCPs electrode as the positive electrode and CNTs/nickel foam (CNTs/NF) as the negative electrode, the device assembled with CR2025 batteries exhibits high energy density (38.39 Wh kg^-1), high power density (5400 W kg^-1 at 9.67 Wh kg^-1), and stable power characteristic (2000 times with 80.63% retention). After charging each supercapacitor for 10 s, the device can power a 5 mm diameter light-emitting diode (LED) with different colors efficiently, for example, a blue LED for 20 min.