Insights on the fundamental capacitive behavior: a case study of MnO2.

In this work, an insightful study on the fundamental capacitive behavior of MnO2 based electrodes is carried out using MnO2 hierarchical spheres (MHSs) and MnO2 nanoneedles (MNs) as examples. An overall understanding of the relationship between the capacitive performance and the electrode configuration as well as the morphology of active material, loading density, porosity of electrode, and electrolyte concentration is investigated comprehensively. Our analyses show that MnO2 with thin structure is of advantage to increase the utility of active material and to deliver higher specific capacitance, as the faradic reaction happens at/near the surface. Creation of an efficient path for the transport of electrons and ions is crucial to achieve high rate capabilities. Cycling stability could be improved by suppressing the side reaction. It is also important to shed light on the charge contribution from a graphite paper (GP) substrate since it may cause a misinterpretation of the capacitive behavior. This study provides a comprehensive understanding on the fundamental capacitive behavior of MnO2 based electrodes and gives useful clues for designing high performance supercapacitors.