Polypyrrole-coated manganese dioxide with multiscale architectures for ultrahigh capacity energy storage

Abstract

For practical nanoscale development, multiscale architectures composed of uniformly patterned nanomaterials are attractive for various applications in electrochemical devices owing to the benefits derived from their unique structures: relatively large surface area, low tortuousness and interconnected pores. However, although various morphological modifications exist, there are no reports about one-dimensional (1-D) nanomaterial based multiscale architectures because of difficulties in the fabrication of uniform 1-D nanostructures. Here we report the demonstration of one-dimensional metal oxide nanostructure-based multiscale architectures that are micronodules composed of ca. 30 nm-diameter MnO₂ nanofibers on carbon cloth to produce energy storage devices. In addition, partially carbonized polypyrrole (CPPy) was coated on the MnO₂ surface through vapour deposition polymerization (VDP) and subsequent heat annealing to give the multiscale micronodules a low resistance and high rate performance. Then, the PPy-coated MnO₂-based multiscale micronodules were assembled within a PVA–KOH polymer electrolyte as the positive-electrodes of solid-state asymmetric supercapacitors (ASCs). This multiscale architecture based device displays ultrahigh performance (59.5 F cm⁻³ of capacitance and 27.0 mW h cm⁻³ of energy density). Furthermore, the as prepared ASCs show high cycle stability and an enhanced charge transfer rate owing to the coating layers.