Preparation And Electrochemical Performanceof Carbon Electrode Materials For Supercapacitors

Supercapacitor is a new energy storage device. With the advantages of its large capacity, fast charge-discharge capability and long cycle life, it has broad application prospects in military, automobiles, telecommunications, aeronautics and astronautics, etc. Since electrode materials play an important role in the properties of supercapacitor, studies on supercapacitors are mainly focused on seeking more desirable electrode materials. In this paper, two kinds of carbon materials were synthesized by different preparation technologies, followed by activation process, and their electrochemical performance was studied.Firstly, the carbon spheres(CSs) were prepared by hydrothermal process using glucose as the raw material, followed by carbonization. Then, the CSs were treated in nitric acid(HNO3) or potassium hydroxide(KOH) to gain activated carbon spheres(ACSs). The results showed that the obtained CSs had nanospherical morphology with a diameter from 120 to 450 nm. After HNO3 or KOH, ACSs with relatively uniform particle size were formed, and the average size of the particles decreased to around 190 nm in diameter. After HNO3 activation, oxygen-containing functional groups on the surface of CSs were detected, which could improve the hydrophilicity of CSs. KOH activation process increased the speci?c surface areas and mesopores on the CSs. Based on the one-step activation process, CSs were also activated by a two-step activation process of HNO3 and KOH. In spite of different roles in activation processes of CSs, HNO3 and KOH activations led to a similar consequence of effective improvement in the capacitance performance of the CS materials. The ACS electrodes exhibited pseudofaradaic capacitance behavior in KOH electrolyte. In 3 M KOH electrolyte, the speci?c capacitance of CSs activated by HNO3, KOH and a two-step activation were 195.7 F/g、206.1 F/g and 232.8 F/g at a current density of 0.5 A/g, respectively. Moreover, the capacitive retention ratios were 89%, 87% and 86%, respectively, after 500 charge/discharge cycles, which exhibited good cycling stability.Then we synthesized biomass carbon(BCs) by the method of carbonization using wood powder as the raw material. We investigated the effects of preparation conditions and HNO3 activation process on electrochemical properties of the BCs. The results revealed that the BCs activated at 70 °C for 6 h in 6 M HNO3 solution appeared the highest capacitance, which was 152.9 F/g at a current density of 0.5 A/g. The capacitive retention ratio was 90% after 500 charge/discharge cycles, which exhibited good cycling stability.In order to combine double layer capacitance with pseudo-capacitance, the BC/Ni O composites with various Ni O ratios were prepared. The results showed that the capacitance of composite electrode reached 250.5 F/g when content of Ni O was 30%, much higher than that of the activated BC electrode. The specific capacitance still retained 84% of initial values after 500 cycles.