Characterization of MnFe2O4/LiMn2O4 aqueous asymmetric supercapacitor

A new type of asymmetric supercapacitor containing a MnFe2O4 negative electrode and a LiMn2O4 positive electrode in aqueous LiNO3 electrolyte has been synthesized and characterized. The nanocrystalline MnFe2O4 anode material has a specific capacitance of 99 F g−1 and the LiMn2O4 cathode a specific capacity of 130–100 mAh g−1 under 10–100 C rate. The cell has a maximum operating voltage window of ca. 1.3 V, limited by irreversible reaction of MnFe2O4 toward reducing potential. The specific power and specific energy of the full-cell increase with increasing anode-to-cathode mass ratio (A/C) and saturate at A/C ∼4.0, which gives specific cell energies, based on total mass of the two electrodes, of 10 and 5.5 Wh kg−1 at 0.3 and 1.8 kW kg−1, respectively. The cell shows good cycling stability and exhibits significantly slower self-discharge rate than either the MnFe2O4 symmetric cell or the other asymmetric cells having the same cathode but different anode materials, including activated carbon fiber and MnO2.