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 Fg(-1) and the LiMn2O4 cathode a specific capacity of 130-100 mAh g(-1) under 10-100C 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 similar to 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. (C) 2010 Elsevier B.V. All rights reserved.
