Controlling the Cooling Rate of Hydrothermal Synthesis to Enhance the Supercapacitive Properties of β-Nickel Hydroxide Electrode Materials

Abstract

The demand for power storage devices with good quality, fast charging and high energy density is becoming more and more urgent in today’s electronic technology. For batteries and traditional capacitors, it is an insurmountable challenge to combine fast charging and discharging, large capacitance and long-life properties. The characteristics of supercapacitors can meet all the above requirements at the same time. In this study, a simple one-step hydrothermal method was successfully used to grow β-nickel hydroxide nanocone particles directly on the 3D foamed nickel substrate as a working electrode material for supercapacitors. After growing β-nickel hydroxide crystals on 3D foamed nickel substrate, by controlling the cooling rate, a well-crystalized β-nickel hydroxide with good capacitance characteristics can be obtained. Cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) were used to analyze the capacitance characteristics of the β-nickel hydroxide electrode. The research results show that the specific capacitance value of the β-Ni(OH)2/3D nickel foam electrode material prepared at the cooling rate of 10 °C/h can reach 539 F/g with the charge–discharge test at a current density of 3 A/g. After 1000 continuous charge and discharge cycles, the material still retains 94.1% of the specific capacitance value.

Preparation of Electrodes with β-Nickel Hydroxide/CVD-Graphene/3D-Nickel Foam Composite Structures to Enhance the Capacitance Characteristics of Supercapacitors

“…In our previous study [ 36 ], we cooled nickel hydroxide to room temperature at three different cooling rates after hydrothermal growth in order to investigate the impact of the cooling rate on the crystallization of nickel hydroxide. Figure 1 shows the XRD patterns of N 100 , N 25 , and N 10 .…”

“…A light-green, clear aqueous solution was produced. This mixed solution and the graphene/nickel foam substrate were placed in a 75 mL hydrothermal autoclave, heated to 200 °C, and maintained under these conditions for 6 h. According to previous research [ 36 ], the crystallinity of nickel hydroxide is optimized at a cooling rate of 10 °C/hour until reaching room temperature. Therefore, the cooling rate after the completion of hydrothermal growth of nickel hydroxide was fixed at 10 °C/hour in this study.…”

“…The specific capacitance value of the working electrode material can be calculated by incorporating the GCD analysis results into the following formula [ 36 ]: …”