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

Abstract

Supercapacitors require excellent cycling stability and rate capability for electrodes. The NiCo 2 S 4 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 NiCo 2 S 4 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 1[Formula: see text]mA/cm 2 , capacitance of these NiCo 2 S 4 nanomaterials is measured as 2.09[Formula: see text]F/cm 2 , 3.22[Formula: see text]F/cm 2 , and 4.42[Formula: see text]F/cm 2 , respectively. It was found that the exposure ratio of (111) and (220) crystal facets also has an effect on electrochemical performance, and NiCo 2 S 4 with I[Formula: see text]/I[Formula: see text] of 3:1 showed better performance. Furthermore, NiCo 2 S 4 -PN//AC asymmetrical supercapacitor was assembled with NiCo 2 S 4 -PN serving as positive electrode and activated carbon (AC) as negative electrode. At a power density of 7.284[Formula: see text]mW/cm 2 , energy density achieved was 0.625[Formula: see text]mWh/cm 2 . 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.