Crystal Facet Control of Nickel-Cobalt Sulfide Nanostructure and Study of Supercapacitor Performance

Supercapacitors require excellent cycling stability and rate capability for electrodes. The NiCo2S4 spinel structure has caught much attention for its high conductivity and high theoretical specific capacity. However, due to the lack of active sites, it has been restricted in supercapacitors. In this research, the NiCo2S4 nano-material with needle, sheet and porous network morphologies were prepared by the addition of different kinds of surfactants via a simple hydrothermal method. At 1mA/cm2, capacitance of these NiCo2S4 nanomaterials is measured as 2.09F/cm2, 3.22F/cm2, and 4.42F/cm2, respectively. It was found that the exposure ratio of (111) and (220) crystal facets also has an effect on electrochemical performance, and NiCo2S4 with I(111)/I(220) of 3:1 showed better performance. Furthermore, NiCo2S4-PN//AC asymmetrical supercapacitor was assembled with NiCo2S4-PN serving as positive electrode and activated carbon (AC) as negative electrode. At a power density of 7.284mW/cm2, energy density achieved was 0.625mWh/cm2. Additionally, capacitance retention rate remained at 79.6% of initial capacitance after 1500 cycles. These outcomes are of great significance for developing more efficient, stable and reliable transition metal sulfide-based supercapacitors.