Preparation And Performance Study Of Electrochemical Capacitor Electrode Materials

Electrochemical capacitor is a charge storage device differing from the traditional electrostatic capacitor and the rechargeable battery. Electrochemical capacitors exhibit many advantages, such as high energy and power density, large charge-discharge rates, long cycling life, high- and low-temperature resistance, and environmental friendliness. As one of the most promising candidates for the next generation of energy storage devices, the electrochemical capacitors show a wide range of applications in aerospace devices, electric vehicle-drive systems, consumer electronics, transportation and military defense systems. Electrochemical capacitors have played an increasing important role in field of power sources.Recently, the trend in developing high-performance electrochemical capacitors is to synthesize hybrid capacitors by combining the two different mechanisms of electrical double-layer capacitors?EDLC? and pseudocapacitor. Electrochemical capacitor electrode materials based on carbonaceous materials, transition-metal oxides and conducting polymers have high energy density and large capacitance, thus can satisfy the requirements of high-performance supercapacitors. Accordingly, the research on high-performance ternary hybrid electrode materials is an ongoing interest.The ternary hybrid electrode materials were prepared succesfully based on carbonaceous materials, manganese dioxide and polyaniline in this paper. The structure and morphology of the prepared samples were characterized by scanning electron microscopy?SEM?, transmission electron microscopy?TEM?, X-ray powder diffraction?XRD? and Fourier-transform infrared spectroscopy?FT-IR?. The electrochemical properties of composites were evaluated by constant current charge-discharge, cyclic voltammetry and AC impedance, respectively. The main contents are as follows:1. High performance actived carbon-MnO₂-polyaniline?AC/MnO₂/PANI? composite was synthesized via a two-step method. AC/MnO₂ was firstly obtained by a aqueous synthesis method, and then exposed to an in-situ polymerization process of aniline under acidic conditions to form the AC/MnO₂/PANI composite. When AC and MnO₂ were mixed in a mass ratio of 1:2, the stable performances of AC/MnO₂ were prepared, which manganese dioxide was made use of the pore structure of activated carbon. The specific capacitance of AC/MnO₂ is 162 F/g, almost 1.28 times higher than that of activated carbon. After 1000 cycles test, AC/MnO₂ still retains 84 % of the initial specific capacitance. Based on this, the AC/MnO₂/PANI ternary composite were synthesized on the surface of AC/MnO₂ by in-situ polymerization. The highest specific capacitance of AC/MnO₂/PANI is 245 F/g under current density of 1 A/g when AC/MnO₂ and PANI were mixed in a mass ratio of 1:2. the capacitance of the AC/MnO₂/PANI remains about 85 % after 1000 charge/discharge cycles at 1 A/g. The results indicate that the AC/MnO₂/PANI composites exhibit good cyclic stability, electrochemical reversibility and a good rate capability.2. The hydrothermal synthesis was employed for the synthesis of Graphene/MnO₂/PANI ternary composite. MnO₂/PANI was firstly obtained by a hydrothermal synthesis method. When MnO₂ and PANI were mixed in a mass ratio of 1:1.5, the stable performances of MnO₂/PANI were prepared, which manganese dioxide was made use of the nano-fibrous structure of PANI. The highest specific capacitance of MnO₂/PANI is 240 F/g. After 1000 cycles test, MnO₂/PANI still retains 85 % of the initial specific capacitance. Based on this, the Graphene/MnO₂/PANI ternary composite were synthesized successfully by adding the graphene. The highest specific capacitance of Graphene/MnO₂/PANI is 305 F/g under current density of 1 A/g when the content of graphene is 40%. The capacitance of the Graphene/MnO₂/PANI remains about 90 % after 1000 charge/discharge cycles at 1 A/g. The results indicate that the Graphene/MnO₂/PANI ternary composites exhibit good electrochemical reversibility, cyclic stability and a good rate capability.