Abstract
Herein, we report a comparison of the electrochemical performance of two kinds of NiCo2S4-based electrodes for solid-state hybrid supercapacitors (HSCs). For the binder-free electrode, NiCo2S4 was grown on Ni foam by the chemical bath deposition (CBD) method. For the binder-using electrode, NiCo2S4 powder was synthesized by the hydrothermal method. FESEM images depicted the hierarchical nanostructure of NiCo2S4 synthesized by the hydrothermal method and uniform distribution of nanostructured NiCo2S4 grown on Ni foam by the CBD method. Half-cell studies of both NiCo2S4 electrodes showed them exhibiting battery-type charge storage behavior. To assemble HSCs, NiCo2S4 and activated carbon were used as a positive and negative electrode, respectively. Electrochemical studies of the HSCs showed that the accessible potential window was wide, up to 2.6 V, through cyclic voltammetry (CV) analysis. Chronopotentiometry (CP) studies revealed that the energy and power densities of binder-using HSC were 51.24 Wh/kg and 13 kW/kg at 1 Ag−1, respectively, which were relatively higher than those of the binder-free HSC. The binder-free HSC showed 52% cyclic stability, relatively higher than that of the binder-using HSC. Both HSCs, with unique benefits and burdens on energy storage performance, are discussed in this work.
Highlights
Supercapacitors store electrical energy in various unusual ways compared to conventional energy storage devices such as batteries and capacitors [1,2]
Carbon-coated Ni foam was used as a current collector and carboxymethyl cellulose and KOH (CMC/KOH) gel as an electrolyte to widen the potential window of the hybrid supercapacitors (HSCs)
The other was a NiCo2S4 powder synthesized by the hydrothermal (HT) method, which was coated on the current collector with PVDF binder without any conductive additives and which served as the binder-using electrode
Summary
Supercapacitors store electrical energy in various unusual ways compared to conventional energy storage devices such as batteries and capacitors [1,2]. In addition to the selection of electrode material and synthesis method, the electrolyte and current collector play critical roles in the performance of HSCs. There are various types of electrolytes used in HSC applications. The current collector should have a high oxidation point and high electrochemical stability [36,37,38] In this present work, carbon-coated Ni foam was used as a current collector and CMC/KOH gel as an electrolyte to widen the potential window of the HSCs. To investigate the intrinsic properties of NiCo2S4 for utilization as a supercapacitor electrode, two kinds of NiCo2S4 electrodes were prepared. The other was a NiCo2S4 powder synthesized by the hydrothermal (HT) method, which was coated on the current collector with PVDF binder without any conductive additives and which served as the binder-using electrode. The loaded masses of NCS(PW) and NCS (CBD) were ~2.4 mg/cm−1
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