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Synthesis of Manganese-Based Electrode Micro/nanomaterials,Characterization and Their Electrochemical Performances

Author: ZhangXing
Tutor: QianYiTai
School: University of Science and Technology of China
Course: Materials Physics and Chemistry
Keywords: hydrothermal solvothermal nanowire nanoplate hierarchical structure specific capacity electrochemical performances manganese oxides lithium-ion batteries
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Type: PhD thesis
Year: 2013
Downloads: 122
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Abstract


In this paper, hydrothermal method was developed to synthesis Mn3O4nanowires with the assistance of sodium borate and without any surfactants or templates; Using the inherent crystal tendency of brucite crystal, combined with the CVD method in acetylene atmosphere, synthesis of a series of MnO@C core-shell nanoplates; In ethylene glycol-water-hydrazine hydrate ternary mixed solvent system, control the synthesis of a series of Mn(OH)2hierarchical structures, combined with solid state method, obtained a series of Mn2O3hierarchical structures. Mn3O4octahedrons were synthesis in water phase at room temperature. The main contents are summarized as follows:1. With the assistance of sodium borate, the Mn3O4nanowires with diameter of-15nm and a length of up to several micrometres have been hydrothermally synthesized at200℃for15h without any surfactants or templates. It was investigated that during the formation process of Mn3O4nanowires the length of the nanowires increased while the diameter did not obviously change, it could be believed that the formation of Mn3O4nanowires followed the Ostwald ripening process. The coercivity of the Mn3O4nanowires is up to5600Oe at5K. As these Mn3O4nanowires were treated with LiOH by solid state reaction at750℃for6h, interconnected LiMn2O4polyhedrons were obtained. The achieved discharge capacity of the LiMn2O4polyhedrons was115mA h g-1and they retained98.3%of this capacity after60cycles at0.1C. The above results of research have been published in CrystEngComm.2. Using the inherent crystal tendency of brucite crystal, Mn(OH)2nanoplates with size of-150nm have been hydrothermally synthesized at180℃for12h. MnO@C core-shell nanoplates with a size of-150nm have been prepared via thermal treatment deposition of acetylene with the precursor of Mn(OH)2nanoplates. The thickness of the carbon shells varied from-3.1to13.7nm by controlling the treatment temperature and reaction duration time. The electrochemical performance of the MnO@C nanoplates, which were synthesized at550℃for10h with a carbon shell thickness of-8.1nm, display a high reversible capacity of-770mA h g-1at a current density of200mA g-1and good cyclability after prolonged testing, which is higher than that of MnO@C nanoplates with a carbon shell thickness of～3.1,4.0,4.2,10.9and13.7nm. The above results of research have been published in J. Mater. Chem.3. Mn(OH)2hierarchical structures were obtained in the ethylene glycol-water-hydrazine hydrate system with different ethylene glycol/water volume ratio. Such as, nanosheets stacking flower structure, nanoplates stacking plate structure, partial fallen stacking plate structure and nanplate. It should be point out that the nanosheet and nanoplates own different thickness.Mn2O3porous hierarchical structures have been fabricated from the Mn(OH)2precursor in air atmosphere at600℃for12h. When these Mn2O3samples used as anode materials for lithium-ion batteries, the Mn2O3porous stacking nanosheets displays a high and stable reversible capacity of～521mA h g-1at a current density of300mA g-1after100cycles. The compared experiments indicate that both thin thickness of nanosheets and porous structure of the Mn2O3are favorable for electrodes of lithium-ion batteries with improved specific capacity and rate performance.4. With the assistance of ammonium oxalate, the Mn3O4octahedrons have been synthesised at room temperature by using the inherent crystal tendency. It investigates the information mechanism, magnetism and electrochemical performances of Mn3O4octahedrons.

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