Hydrothemal Synthesis,morphological Characterization, And Studies On Electrochemical Properties Of Manganese Oxides

In this thesis, manganese dioxide which have a series of different crystal structures and morphologies, have been prepared by a hydrothermal method. The crystal structure, morphology and electrochemical performance of productions have been studied deeply by X-ray diffraction (XRD), inductively coupled plasma atomic emission spectrometry (ICP-AES), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric - differential thermal analysis meeting (TG-DTA), field emission scanning electron microscopy ( FESEM) , electrochemical workstation and so on. The conclusion is summarized as follows:Nanomanganese dioxide was synthesized by hydrothermal method which used KMnO4 and MnSO4 as precursors. By investigating the influence of different hydrothermal reaction conditions, such as time, temperature and acidity, on the crystal structure, theα-MnO2 nanoclud was acquired. Results show that reaction time and temperature have little influence on the crystal structure of MnO2, but the Crystallinity of MnO2 increase with increasing reaction temperature. Keep the hydrothermal reaction time and temperature as constant, when increasing acidy of solution, the crystal structure of MnO2 change fromα-MnO2 to amorphous MnO2. Thus under alkaline conditions, it is more conducive to the formation of amorphous manganese dioxide.Discharge performance ofα-MnO2 which made under different conditions was tested by electrochemical workstation. The discharge capacity ofα-MnO2 is 150mAh/g which made under 24 hours, 140℃and solution pH of 1.5, it is the best in all. MnSO4, Mn (NO3)2 and MnCl2 were used as reducing agent, than reacted with KMnO4. Research the influence of anions on the crystal structure, morphologies and electrochemical properties of production. Results indicate that theγ-MnO2 forme only in NO3- or Cl- solution. Under the same concentration of K+, SO42- is propitious to formα-MnO2. The initial discharge capacity ofα-MnO2 which containedγ-MnO2 is 203 mAh / g, higher than single-phaseα-MnO2.To improve the cycle charge-discharge performance ofα-MnO2, we synthesized La-dopingα-MnO2 and studied its charge-discharge capability. La3+ can dope well intoα-MnO2 structure without forming La2O3 phase. When La/Mn was equal 0.0029, La could effectively improve charge-discharge capability ofα-MnO2. The initial charge capacity is 122.7 mAh/g, and then decrease to 101 mAh/g after 28 charge-discharge cycles. Attenuation capacity account for 17.7% of initial discharge capacity, far lower than 66.4﹪of La-undopingα-MnO2. The initial discharge capacity of La-dopingα-MnO2 decrease with increasing La/Mn, and capacity fade seriously.Studies show that doping amount of La element, can improve the cycle charge-diacharge performance of MnO2, and effectively inhibite the capacity of MnO2 to attenuate. It can meet the requirements of the battery material.