Direct ultrasonic modification of a current collector with enhanced pseudocapacity†
In this study, we used a direct ultrasonic modified nickel foam in sulfuric acid, which achieved a simple and rapid binder-free electrode, improving the electronic transmission in the electrolyte. It produced a bed of electroactive nickel hydroxide and sulphide with a unique needle-like microstructure, which grew vertically on the surface of the Ni foam straight into the electrolyte, not only increasing the contact interface area between the active material and the electrolyte but also shortening the diffusion length of the ions. The obtained product possesses outstanding electrochemical performance, having a high specific capacitances of 6 F cm−2 at a current density of 5 mA cm−2, which can still retain 2.2 F cm−2, even at a current density as high as 40 mA cm−2. Furthermore, it has excellent cyclic stability with only 5% loss after 1000 cycles.