Structure Construction And Supercapacitor Performance Of Cobalt-Based Electrode Materials

With the rapid consumption of traditional fossil fuels and the associated serious environment problems which are brought by the excessive using of the fossil fuels, the research and development of new energy materials are very necessary. The experts and scholars of all over the world have done much research about supercapacitors which have high power densities, long cycling life, low cost and environmental friendliness. Compared to the lithium ion batteries, the energy densities of supercapacitors are very low, which is far away to satisfy the energy storage devices with high energy densities. So the development of high energy density supercapacitors is becoming the key point in the field of supercapacitors. Particularly, the study of supercapacitor electrode materials with high performance is the main issue in this research project. While, the obtaining of supercapacitor electrode materials with high capacitance, superior reversibility, excellent stability and good rate capability are still the tremendous challenge in the energy storage field. To our knowledge, few research results could successfully achieve the electrode materials with the above comprehensive electrochemical performance simultaneously.Based on the research objects of cobalt-base compounds, we designed and elaborated one special interwoven three-demensional(3D) frame architecture of cobalt oxide nanobrush-graphene@NixCo2x(OH)6x(CNG@NCH) electrode with high comprehensive electrochemical performance through a facile modified hydrothermal method followed by two-step calcination and two-step optimized electrodeposition. Additionally, we also did some relevant detail analysis of this interwoven three-dimensional frame structure material to confirm the advantages of this structure design. More importantly, our 3D frame architecture material successfully overcomes the tremendous challenge for pseudocapacitor electrode materials with high comprehensive electrochemical performance and it also can provide a promising structure design direction for optimizing the electrochemical performance of various electrode materials. The main research results are as follows:(1) We synthesized different cobalt oxide materials with various morphologies through the modified hydrothermal method and two-step calcination and the cobalt oxide nanobrush material has never been reported before. In order to find out the optimal sample and obtain the relationship between the morphologies and the electrochemical properties, we tested the electrochemical performance of different cobalt oxide materials.(2) The cobalt oxide nanobrush decorated with graphene presents high specific capacitance and good rate capability. Its specific capacitance decreases from 2579 to 2355 F/g corresponding to 91.31% capacitance retention when the current densities vary from 1 to 20 A/g. The good performance demonstrates that cobalt oxide nanobrush-graphene can be the suitable backbone material for the later nanostructure design.(3) We synthesized interwoven 3D frame architecture of cobalt oxide nanobrush-graphene@NixCo2x(OH)6x(CNG@NCH) electrode through a facile modified hydrothermal method followed by two-step calcination and two-step optimized electrodeposition. The electrochemical results show that the specific capacitance of this sample is 2550 F/g(5.1 F/cm2) at the current density of 1 A/g, even if at the current density of 20 A/g, its specific capacitance still can reach up to 2116 F/g(4.23 F/ cm2), which has 82.98% capacitance retention. After 5000 cycles, it possesses 92.70% capacitance retention at a current density of 20 A/g.(4) We fabricated the full supercapacitor in which the positive electrode is cobalt oxide nanobrush-graphene@NixCo2x(OH)6x and the negative electrode is RGOF. The electrochemical results show that the energy density value of our obtained full supercapacitor is among the advanced level in the field of supercapacitor. The highest energy and power densities can reach up to 78.75 Wh/Kg and 8424.25 W/Kg, respectively. After 5000 cycles at 10 A/g, the capacitance retention is 99.15%.