Preparation of Spherical δ-MnO Nanoflowers by One-Step Coprecipitation Method as Electrode Material for Supercapacitor.

Spherical δ-MnO nanoflower materials were synthesized via a facile one-step coprecipitation method through adjusting the molar ratio of KMnO to MnSO. The influence of the molar ratio of the reactants on the crystal structure, morphology, and electrochemical performances was investigated. At a molar ratio of 3.3 for KMnO to MnSO, the spherical δ-MnO nanoflowers composed of nanosheets with the highest specific surface area (228.0 m g) were obtained as electrode materials. In the conventional three-electrode system using 1 M NaSO as an electrolyte, the specific capacitance of the spherical δ-MnO nanoflowers reached 172.3 F g at a current density of 1 A g. Moreover, even after 5000 cycles at a current density of 5 A g, the GCD curves remained essentially unchanged, and the specific capacitance still retained 86.50% of the maximum value. The kinetics of the electrode reaction were preliminarily studied through the linear potential sweep technique to observe diffusion-controlled contribution toward total capacitance. For the spherical δ-MnO nanoflower electrode material, diffusion-controlled contribution accounted for 65.1% at low scan rates and still remained significant at high scan rates (100 mV s), indicating excellent utilization efficiency of the bulk phase. The as-fabricated asymmetric supercapacitor HFC-7//MnO-3.3-ASC presented a prominent specific energy of 16.5 Wh kg at the specific power of 450 W kg. Even when the specific power reached 9.0 kW kg, the energy density still retained 9.5 Wh kg.