Molten salt synthesis of Mn2O3 nanoparticle as a battery type positive electrode material for hybrid capacitor in KNO3-NaNO2-NaNO3 melts

An innovative kind of low-temperature inorganic molten salt hybrid capacitor was first put forward. Mn2O3 nanoparticle was selected as battery type positive electrode of hybrid capacitor. The high crystallinity Mn2O3 nanoparticles with large specific surface areas were successfully prepared by molten salt synthesis method using ternary alkali nitrates. Electrochemical performances of Mn2O3 electrode were evaluated by cyclic voltammetry, square wave voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge in KNO3 (53 wt%)-NaNO2 (40 wt%)-NaNO3 (7 wt%) melts at 423 K. The results illustrated that Mn2O3 electrode transferred one electron during the reduction reaction and the Mn2O3 nanoparticle exhibited a high specific capacity of 669.6 C g−1 (186.0 mAh g−1, 2.51 F cm−2) at a current density of 5 mA cm−2. Furthermore, Mn2O3 electrode exhibited excellent cycle stability, and the capacity retention was up to 90.2% after 5000 cycles at a current density of 20 mA cm−2. The hybrid capacitors with molten salt electrolyte could be considered as a potential application in some specific situation which requires the high-temperature demand.