Three-Dimensional Arrays of 1D MnO₂ Nanocrystals for All-Solid-State Asymmetric Supercapacitors

Reported is the synthesis of 3D hierarchical structures based on one-dimensional MnO₂ nanobuilding blocks (nanorods, nanowires, and nanoneedles) by means of a facile and scalable coprecipitation method and their use as electrodes for the assembly of all-solid-state supercapacitors. Asymmetric devices were also assembled by using these nanostructured MnO₂ materials as the positive electrode and reduced graphene oxide (rGO) as the negative electrode with a polymeric gel electrolyte. The asymmetric cells successfully extend the working voltage windows beyond 1.4 V and allowed for a maximum voltage of 1.8 V. An asymmetric device based on hierarchical nanoneedle-like MnO₂ and rGO achieved a maximum specific capacitance of 99 F g^-1 at a scan rate of 10 mV s^-1 with a stable operational voltage of 1.8 V. This high value allowed for a large specific energy of 24.12 Wh kg^-1 .