A novel ordered hollow spherical nickel silicate–nickel hydroxide composite with two types of morphologies for enhanced electrochemical storage performance
Herein, a facile strategy was developed for the preparation of a nanostructured nickel silicate–nickel hydroxide composite (NiSi–Ni(OH)2) with two types of morphologies, including coated hollow nanospheres (NiSi@Ni(OH)2) and platelet-assembled hollow spheres (Ni(OH)2-Si) as a positive electrode material in hybrid supercapacitors. This strategy involved the use of nano-sized SiO2 derived from the Stöber method as the silicon source and a single-step hydrothermal method. The as-synthesized NiSi–Ni(OH)2 composite exhibited a battery-like redox behavior and relatively high charge storage property (476.4 F g−1 at 2 A g−1) when measured in a three-electrode system. It also delivered high stability during long-term cycling (103.3% after 10 000 cycles), which is mainly due to the synergistic effect after the combination of the two materials, where the hollow spherical structures facilitate the fast diffusion of electrolyte ions and enable the fast transmission of electrons. Considering its practical applications, a hybrid asymmetric supercapacitor (HSC) device was assembled using NiSi–Ni(OH)2 as the positive electrode and porous activated carbon as the negative electrode in PVA–KOH electrolyte gel. The HSC exhibited a capacitance of 674.7 mF cm−2 at 2 mA cm−2, corresponding to a maximum energy and power density of 21.6 W h kg−1 (5.2 W h cm−3) and 431.7 mW kg−1 (104.3 mW cm−3), respectively. These properties demonstrate the potential of the hollow-structured NiSi–Ni(OH)2 composite for achieving high-energy and stable energy storage systems.