NiCo‐glycolate‐derived porous spherical NiCo2S4 for high‐performance asymmetric supercapacitors

Abstract

The construction of electrode materials with high rate and excellent cycling stability is the key to supercapacitors. Due to their remarkable high conductivity and great electrochemical activity, transition bimetallic sulfides are extremely appealing electrode materials for supercapacitors, but their synthesis is still challenging. In this study, a NiCo bimetallic sulfide (NiCo2S4) microspheres with porous structure were prepared via direct vulcanization of NiCo‐EG complexes followed by a thermal treatment, which were pre‐synthesized via coordination of ethylene glycol (EG) with transition metal ions (Ni2+, Co2+) under hydrothermal condition. Some experimental parameters were investigated, including the control of NiCo2S4 microspheres produced by the ratio of precursor NiCo‐EG to different masses of sulfur sources, which in turn affects the electrochemical properties. When applied as electrode for supercapacitor, the NiCo2S4 microspheres obtained under optimal condition delivered a high capacitance (1386 F g−1 at 1 A g−1), excellent rate capability (845 F g−1 at 10 A g−1) and stable cycling performance (80.05% after 5000 cycles at 10 A/g). Furthermore, for checking the practicality of the produced NiCo2S4 microspheres, an asymmetric supercapacitor device was built using activated carbon (AC) as the negative electrode and NiCo2S4 microspheres as the positive electrode. The assembled NiCo2S4//AC cell had a power density of 799.9 W kg−1 and an energy density of 30.5 Wh kg−1, confirming that the structurally optimized NiCo2S4 porous nanomicrospheres have excellent electrochemical properties and have a wide range of application prospects.