Amorphous-crystalline CoMoS4 with high mass loading for high-performance asymmetric supercapacitors

Abstract

CoMoS4 as electrode material in supercapacitors is attributable to the high theoretical capacitance of CoSx and MoS2. However, there is still room for improvement in its capacitive performance. Besides, electrode material possessing good electrochemical properties is usually restricted to low mass loading. In this work, four amorphous-crystalline CoMoS4 materials were obtained by a precipitation process through altering additive in a mixed solution and subsequent by a thermal treatment process. As-synthesized four CoMoS4 materials consist of numerous amorphous phase accompanying with a very few crystalline phase as well as display different morphology and structure. All CoMoS4 materials with high mass loading achieve high specific capacitance. At 0.5 A g−1, CoMoS4–1, CoMoS4–2, CoMoS4–3, and CoMoS4–4 possess a specific capacitance of 1720.9, 2560.6, 1914.5, and 2498.7 F g−1, respectively. Amongst the four CoMoS4, CoMoS4–2 delivers the highest specific capacitance at 0.5∼4 A g−1. However, the specific capacitance of CoMoS4–3 reaches the largest value at 8∼16 A g−1. CoMoS4–3 and CoMoS4–1 exhibit good rate capability, much better than those of CoMoS4–2 and CoMoS4–4. CoMoS4–3 owns good comprehensive supercapacitive performances related to its optimum amorphous-crystalline ratio, suitable morphology and structure. The assembled CoMoS4–3//AC asymmetric supercapacitor (ASC) using CoMoS4–3 as the positive electrode and activated carbon (AC) as the negative electrode provides a superior energy density (59.2 Wh kg−1 at 425 W kg−1), which is superior to those of previously reported CoMoS4-based ASC devices. In addition, the ASC device displays a satisfactory cycle stability of 85.5% after 2000 cycles at 2 A g−1. This work shows a promising material applied in supercapacitors.