| Summary: | A divalent Mn-Ni oxide solid solution electrode was prepared by a hydrothermal method, and its electrochemical characteristics were investigated. As a result of optimizing preparation and heat treatment conditions and including nanocarbon as a conducting material, the potential window of electrode was successfully enlarged compared to that previously reported, reaching a specific capacitance of 363 F g−1. An aqueous electrolyte asymmetric supercapacitor consisting of electrodes of the Mn-Ni oxide including carbon (Mn-Ni-O/C) and activated carbon operated to an upper limit voltage of 2.5 V, leading to an energy density of 21.0 Wh kg−1 and an average power density of 21.8 kW kg−1. Moreover, the relationship between the oxidation number and the potential of the electrode was studied by X-ray photoelectron spectroscopy. For the first time, the oxidation number of Mn in the electrode was observed to change approximately in the range from divalent to tetravalent during the charge-discharge. This can be a very important guideline for increasing the capacitance and energy density of the Mn-based oxide electrodes.
|
|---|