Insights on the fundamental capacitive behavior: A case study of MnO ₂

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 MnO ₂ based electrodes and gives useful clues for designing high performance supercapacitors. This study shows that MnO₂ with thin structure is of advantage to achieve higher specific capacitance. An efficient path for the transport of electrons and ions is crucial to achieve high rate capability. Cycling stability could be improved by suppressing side reactions. In addition, charge contribution from graphite paper substrate is also important since it may cause misunderstanding of capacitive behavior.