Nanostructured manganese dioxides as active materials for micro-supercapacitors

This Letter presents the design, synthesis and characterisation of nanostructured manganese dioxides (MnO₂) and their composites as electrode materials for high-capacity micro-supercapacitors. Three MnO₂ samples have been synthesised by liquid-phase reaction processes, and characterised by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, surface area measurement and electrochemical tests. As a result, a preferred composite containing nano-MnO₂ powder as active material, acetylene black as conductive agent and polyvinylidene fluoride as binder, exhibits a specific capacitance as high as 160 F/g in 0.2 M K₂SO₄ aqueous solution. Then a micro-supercapacitor device with 3D interdigital structure using the composite material as electrodes has been achieved by MEMS fabrication technology. The micro-supercapacitor has well-performed capacitive behaviour under various scan rates and has a large specific capacitance of 30 mF/cm² in terms of footprint area or 50 F/cm³ in terms of effective volume, which indicates that the composite is a promising material for energy storage on chips.