The Preparation Of Manganese Oxide And Its Electrochemical Properties Of Spherical Shape

Manganese oxide materials have been widely applied in supercapacitor and lithium ion secondary battery due to their low cost and the excellent electrochemical properties. In this thesis, Mn3O4and MnO with microsphere morphology have been prepared by a solvothermal treatment, and their structure and morphology are systematically investigated by XRD, XPS, and SEM. The relationship between the capacitance and structure for the obtained materials is studied by using Mn3O4microsphere as the supercapacitor electrode material. Also the battery property is investigated by using MnO as the anode material.This thesis mainly consists of three sections, reviewer, experiment and conclusion. Introduction part (chapter1) reviews the structure, classfication, preparation method and the appplication of manganese oxide materials. Mn3O4with microsphere morphology has been synthesized by a solvothermal treatment, and the relationship between the capacitance and structure for the obtained materials is studied by using Mn3O4microsphere as the supercapacitor electrode material (chapter2). By using the similar reaction system, MnO with microsphere morphology has been synthesized, and its battery property has also been studied in chapter3. The research conclution is finally presented in chapter4.Mn3O4microsphere with diameter about2μm 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℃). The optimatic preparation conditions are as follows:oleic acid (0.2mmol) and manganese (II) acetate tetrahydrate (0.5mmol) are dissolved into absolute ethanol (15mL). The obtained suspension is transferred to a25mL Teflon-lined stainless steel autoclave, maintained at120℃for36h and cooled naturally to room temperature, the resulting precipitate is centrifuged, thoroughly washed with ethanol for three times and dried for12h at50℃in air, Mn3O4microsphere is obtained. The morphology of Mn3O4microsphere is controlled by the amount of oleic acid and the reaction temperature. The capacitance performance of Mn3O4microsphere as electrode material is tested using cyclic voltamogramm technique at a scan rate of10mV s-1in1M Na2SO4solution within a potential window ranging from-0.2to0.8V. Mn3O4microsphere electrode material can be electrochemically oxidized to layered birnessite MnO2with flowerlike morphology and pseudoconstant using potential cycling. A capacity improvement of Mn3O4microsphere based electrode upon cycling can be observed for400cycles, and its specific capacitance is significantly improved from10F g-1(after1cycle) to219F g-1(after400cycles). The obvious capacitance improvement is ascribed to the activation effect of the electrochemical cycling and a structural transformation.By changing the solvothermol temperature (180℃) and the amount of oleic acid (3mmol), MnO with microsphere morphology has been prepared in the same reaction system, and the materials have uniform size of about1μm in diameter. The optimatic preparation conditions for MnO microsphere are as follows:oleic acid (3mmol) and manganese (Ⅱ) acetate tetrahydrate (0.5mmol) are dissolved into absolute ethanol (15mL). The obtained suspension is transferred to a25mL Teflon-lined stainless steel autoclave, maintained at180℃for36h and cooled naturally to room temperature, the resulting precipitate is centrifuged, thoroughly washed with ethanol for three times and dried for12h at50℃in air, MnO microsphere is obtained. The morphology of MnO microsphere can be controlled by amount of oleic acid and reaction time. The electrochemical performance of MnO is investigated by a charge/discharge test. The research results indicate that the material has a high initial discharge capacity and shows good battery performance.