Single-step microwave mediated synthesis of the CoS2 anode material for high rate hybrid supercapacitors

A short time microwave irradiation based synthesis method of phase pure cubic CoS2 nanoparticles is reported in this study for the first time. The energy density (ED) of hybrid supercapacitors based on CoS2 as an anode having activated carbon as a cathode has been enhanced by using the higher operating potential of organic electrolytes and by increasing the concentration of the mobile ionic species at the negative electrode, in addition to the lithium ions present in the electrolyte. The specific capacitance delivered by non-lithiated CoS2 nanoflakes was 52 F g(-1) at a current rate of 0.7 A g(-1) between 0 and 3 V using a LiPF6-based electrolyte. Increasing the concentration of the mobile ionic species, i.e., lithium, at the anode enhanced the performance of the hybrid supercapacitor to 119 F g(-1) at a current rate of 0.7 A g (1). The hierarchical arrangement of pores in the electroactive material allowed high electrolyte access and reduced the length of the ionic pathway. Consequently, the lithiated form exhibited an ED of 37 W h kg(-1) with a power density of 1 kW kg(-1) at a current rate of 0.7 A g(-1), compared to only 15 W h kg(-1) for the non-lithiated sample. Furthermore, both samples maintained superior stability over extended cycling for 10 000 cycles at a very high PD of 4 kW kg(-1) with a capacitance retention of 100% for the lithiated sample and 80% for the non-lithiated sample. These results will be useful in the fabrication of high ED, high rate hybrid supercapacitors for electric vehicle applications.