High performance asymmetric supercapacitor based on MnO2 electrode in ionic liquid electrolyte

In this work, the electrochemical properties of a MnO2 nanocomposite electrode were investigated in 1-butyl-3-methyl-imidazolium hexafluorophosphate ([Bmim]PF6)/N,N-dimethylformamide (DMF) electrolyte. The [Bmim]PF6/DMF electrolyte with different volume fractions exhibits significant influence on the electrochemical properties of the electrode. When the volume ratio of [Bmim]PF6 and DMF was 1 : 1, the electrode showed the best electrochemical performance. The operation potential window of the MnO2 nanocomposite electrode in ionic liquids was 2.1 V and the specific capacitance according to the mass of MnO2 was 523.3 F g−1 at 3 A g−1. Then, a high-voltage (3 V) MnO2 asymmetric supercapacitor was successfully fabricated, using the MnO2 nanocomposite electrode, activated carbon and [Bmim]PF6/DMF as the positive electrode, negative electrode and electrolyte, respectively. The MnO2 asymmetric supercapacitor displayed a maximum specific energy of 67.5 W h kg−1 at a specific power of 593.8 W kg−1 and a maximum specific power of 20.4 kW kg−1 at a specific energy of 8.5 W h kg−1. The impressive results showed that [Bmim]PF6/DMF could be a promising electrolyte for MnO2 supercapacitors.