Cage-like MnO2-Mn2O3 hollow spheres with high specific capacitance and high rate capability as supercapacitor material

This study presents the preparation of novel cage-like MnO2-Mn2O3 particles that have high surface area and macro-porosity. Carbonaceous (C) spheres were first prepared hydrothermally as templates for a subsequent hydrothermal step of MnO2 shell precipitation. Adjusting the Mn precursor concentration and hydrothermal dwell time resulted in MnO2 shells of different thickness. Following calcination to remove carbon, thinner shells resulted in cage-like structure and a higher degree of Mn2O3 content, while thicker shells produced complete hollow spheres. The cage-like MnO2-Mn2O3 hollow spheres (CMHS) produced a 30% larger specific capacity than that of complete hollow spheres at 0.05 A g−1. On a 100 fold current density increase to 5 A g−1 CMHS had a 49.9% of its initial specific capacitance, and had 77.4% capacitance retention after 2000 cycles at 2 A g−1. Cage-like particles, through their high surface area and macro-porosity, thus afford a promising target structure for supercapacitor materials, and can be prepared as described herein.