One-Step Solvothermal-Processed 3D Spinel-Type Manganese Oxide Microspheres and Their Improved Supercapacitive Properties

Three-dimensional (3D) spinel-type MnO2 has attracted extensive interest as a potential electrode material for supercapacitors in order to meet cost/performance requirements of power supplies. In this study, MnO2 microspheres (MS-MnO2) with a 3D spinel phase and 0.5-4.0 pm size were constructed from small MnO2 nanoparticles by a rapid and facile solvothermal process in which tetraethylammonium (TEA) was used as the template. The properties of the synthesized spinel MS-MnO2 for use in supercapacitors were investigated by cyclic voltammetry and galvanostatic charge/discharge measurements using a three-electrode system in a neutral 1 M Na2SO4 electrolyte. The synthesized spinel MS-MnO2 exhibited faster charge/discharge rates and higher capacitance than commercial MnO2 materials. The obtained results showed that the as-prepared spinel MS-MnO2 possessed good specific capacitance (SC) of similar to 190 F/g at 0.5 A/g. The spinel MS-MnO2 also exhibited excellent SC retention and Coulombic efficiency of similar to 100% and similar to 95%, respectively, after 1000 cycles at 1 A/g, suggesting its potential application in supercapacitors. In addition, manganese oxides with large cavities were obtained through postannealing treatment and showed their potential for use in energy-storage devices, energy-conversion systems, catalysts, and sensors.