Advanced electrode materials and fabrication of supercapacitors

Abstract

Supercapacitors (SCs) have generated significant interest due to their advantages including lightweight, rapid charge-discharge, good rate capability and high cyclic stability. Electrodes are one of the most important factors influencing the performance of SCs. MXene is a promising candidate for supercapacitor electrodes, which is a relatively new material with formula Mn+1XnTx, where M is a transitional metal, X stands for C or N, and Tx is surface terminations. Due to its multi-layered structure, high surface area and rich redox chemistry, good electrochemical performance can be expected. To further enhance the conductivity of the MXene electrodes, multi-walled carbon nanotubes (MCNT) were applied as the conducting additive. The as-fabricated composite electrodes showed reduced resistance and enhanced electrochemical performance. Advanced co-dispersants such as cationic celestine blue (CCB) and anionic catechol violet (ACV) were employed to improve the dispersion of components. CCB and ACV can adsorb strongly on the MXene and MCNT surface to form a homogenous suspension and thus improve the mixing between them. Another advanced dispersant 3,4,5-trihydroxybenzamide (THB) also showed adsorption on both MXene and MCNT particles, favored their dispersive mixing and improved electrochemical performance. Iron oxides are promising materials for negative electrodes for supercapacitors. The attempt to combine highly capacitive Fe3O4 with MXene-MCNT composites proved the synergistic effect of individual components. Investigation of Zn-doped FeOOH as high active mass loading anode with MCNT as conducting additive allowed for enhanced performance. Zn-Fe double hydroxide materials are promising for the fabrication of advanced supercapacitor electrodes. A safe and neutral Na2SO4 electrolyte was was beneficial for the development of asymmetric devices with enlarged voltage window. For cathodes working in an overlapping window with Zn-FeOOH anode, polypyrrole coated carbon nanotube electrode was fabricated with a comparable capacitance. The advanced dopant eriochrome cyanine R (ECR) allowed for the uniform thickness of PPy coating on MCNT and enhanced charge transfer between PPy and MCNT was achieved. Enhanced capacitive properties of cathodes and anodes at high active mass loading working in complimentary voltage windows allowed for fabrication of high-performance supercapacitor, which was a promising device for practical applications.