Thicker carbon-nanotube/manganese-oxide hybridized nanostructures as electrodes for creation of fiber-shaped high-energy-density supercapacitors

This work demonstrates a high-energy-density and flexible supercapacitor as a potential energy source for smart electronics devices. Cathode and anode are fiber-shaped electrodes with manganese oxide (MnO₂) being electrochemically inserted into densely interconnected carbon nanotube (CNT) networks as active domains, while carbon fibers (CF) serve as current collectors. The CNT/MnO₂ hybrids are built up as a co-axial shell with an optimized thickness of 1.44 μm surrounding CF. Specific volumetric capacitance is found as high as 527 F cm⁻³ when a 1.0 M Na₂SO₄ aqueous solution is used as electrolyte; when a solid electrolyte (polyvinyl alcohol and lithium chloride, PVA/LiCl) is used, the specific volumetric capacitance is found as high as 492 F cm⁻³. These values, to the best of our knowledge, are the highest values of the specific volumetric capacitance among all the MnO₂-based fiber-shaped electrodes reported in previous literature. An all-solid-state (PVA/LiCl) symmetric fiber-shaped supercapacitor cell is assembled and a volumetric energy density of 8.14 mWh cm⁻³ which is high enough for driving a portable LED device, is obtained. Our fiber-shaped supercapacitor cell is safe, flexible, and capable of powering smart electronic devices.