Individual and Bipolarly Stacked Asymmetrical Aqueous Supercapacitors of CNTs/SnO[sub 2] and CNTs/MnO[sub 2] Nanocomposites

Asymmetrical supercapacitors with aqueous electrolytes were fabricated from carbon nanotubes (CNTs) individually coated with and as the negative and positive electrodes, respectively. The nanocomposite is used as the negative electrode material in an asymmetrical supercapacitor. The physicochemical properties of the and nanocomposites were examined by X-ray diffraction, scanning and transmission electron microscopy, cyclic voltammetry, and galvanostatic charge–discharge. Individually, the supercapacitors were tested for charge and discharge to a cell voltage of 1.70 V in 2.0 M KCl without noticeable water decomposition. The asymmetrical cell could reach the specific energy of 20.3 Wh/kg, which is comparable to that obtained from electric double-layer supercapacitors using organic electrolytes . The maximum specific power of the cell, 143.7 kW/kg, is perhaps the highest among all reported aqueous asymmetrical supercapacitors. It also shows an exceptional stability of over 1000 cycles, with the capacity loss being less than 8%. A 10 V stack was also constructed with nine individual supercapacitors connected through bipolar electrodes of the nanocomposites and porous separators containing 1.0 M . The stack exhibited remarkable capacitive behavior resulting from the individual cells.