High-performance asymmetric supercapacitors based on monodisperse MnO nanocrystals with high energy densities.

Monodisperse spherical MnO nanocrystals (NCs) with a size of 22.5 nm were synthesized by the thermal decomposition of manganese oleate in the presence of oleic acid and 1-octadecene. The as-synthesized MnO NCs show superior electrochemical performances with a specific capacitance of 736.4 F g-1 at a current density of 1 A g-1 and retain 93.3% of initial specific capacitance after 5000 cycles. The MnO NC electrode was successfully assembled in an asymmetric supercapacitor as the cathode with an activated carbon (AC) electrode as the anode. The as-fabricated device can demonstrate remarkable performance with an energy density of 44.2 W h kg-1, a power density of 900 W kg-1, and excellent cycling stability. This work provides a new direction for MnO nanomaterials towards high-performance energy storage devices.