Synthesis of novel Mn3O4 microsphere and its distinctive capacitance change during electrochemical cycling

Novel Mn3O4 microsphere with diameter about 2 μm and smooth surface has been prepared by solvothermal treating a mixture of manganese (II) acetate tetrahydrate and oleic acid in absolute ethanol at a low temperature (120 °C), and its structure and morphology are systematically investigated by XRD, XPS, and SEM. The morphology of Mn3O4 microsphere is mainly controlled by adding oleic acid and the size and regularity of Mn3O4 microsphere depend on the solvothermal treatment temperature and time. The capacitance performance of novel Mn3O4 microsphere as electrode material is tested using cyclic voltamogramm technique at a scan rate of 10 mV s− 1 in 1 M Na2SO4 solution within a potential window ranging from − 0.2 to 0.8 V. Mn3O4 microsphere electrode material can be electrochemically oxidized to layered birnessite MnO2 with flowerlike morphology and pseudoconstant using potential cycling. A capacity improvement of Mn3O4 microsphere based electrode upon cycling can be observed for 400 cycles, and its specific capacitance is significantly improved from 10 F g− 1 (after 1 cycle) to 219 F g− 1 (after 400 cycles). The obvious capacitance improvement is ascribed to the activation effect of the electrochemical cycling and a structural transformation.