Electrochemical performance of a high cation-deficiency Li2Mn4O9/active carbon supercapacitor in LiNO3 electrolyte

A hybrid supercapacitor based on spinel Li2Mn4O9 and activated carbon (AC) was fabricated. The electrochemical performance of the capacitor was studied by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge in different aqueous electrolytes such as 1 M LiNO3, Li2SO4, NaNO3 and KNO3 solution. A maximum specific capacitance of 261 F g−1 was obtained for the Li2Mn4O9 single electrode between 0 and 1.4 V. The Li2Mn4O9/AC hybrid supercapacitor showed a sloping voltage profile from 0 to 1.4 V and delivered an energy density of 53 Wh kg−1 based on the total weight of the active electrode materials. The hybrid capacitor exhibited a desirable profile and maintained over 80% of its initial energy density after 1000 cycles, indicating that Li2Mn4O9 has excellent cycling performance and structural stability in aqueous electrolyte. The hybrid supercapacitor also exhibited an excellent rate capability, even at a power density of 1250 W kg−1, it had a specific energy 29 Wh kg−1 compared with 48 Wh kg−1 at the power density of about 417 W kg−1.