The Preparation Of Manganese Oxide Electrode Materials And Their Capacitance Characteristic In Alkaline Solution

Manganese oxides are considered to be a promising material for supercapacitors because of their high theoretical specific capacitance, natural abundance and evirounmentally friendliness. The practical capacitive behavior of manganese oxides is, however, far from the theoretical value due to their poor electrical conductivity and mechanical instability. The manganese oxide with various crystalline structures and morphologies are prepared by controlling the preparation conditions. Element doping and carbon coating are used to realize the modification of manganese oxide. In this paper, the microstructure and the mechanism of property improvement are researched in alkaline electrolyte.Birnessite-type manganese oxide grain particles were successfully prepared via a simple liquid-phase reaction method. The electrochemical performance enhanced by introduce of aluminum or cobalt ion. FT-IR and XPS demonstrate that aluminum influences the binding energy of Mn and strengthens Mn–O bond energy. The in situ pH test shows that the addition of impurity ions decreases the reaction rate, and then decreases the aggregation. As a result, the electrochemical properties are increased.Cerium-doped nanosheet-based porous δ-MnO2 microspheres have been successfully prepared via a simple hydrothermal process. Electrochemical measurements showed that appropriate amount of cerium doping can significantly increase the speicific capacitance of δ-MnO2. In terms of ion transport kinetics, cerium doping can shorten the diffusion path length and increase the ion transfer rate by changing the partical size, porosity density and conductivity of manganese oxides materials.Mesocrystal Mn2O3 was prepared by thermal decomposition of MnCO3 precursor. The morphology can be controled by changing the content of glucose and by adjusting the proportion of ethanol in solvent. Compared with nano Mn2O3, the specific capacitance of mesocrystal Mn2O3 has a remarkable enhancementt.Porous Mn3O4 hexagonal nameplates were synthesized by a hydrothermal method and heating treatment. The morphology and size of the manganese oxideswere controlled by carefully adjusting the concentrations of both KOH and glucose. KOH controls the formation of poresand the shape of the nanoplates, while the glucose can passivate the(001) face and thereby influence the growth and stack behaviors of the nanosheets. The Mn3O4-based electrode shows an excellent high-rate electrochemical performance and good cycle stability. The asymmetric supercapacitor exhibited a high performance with an energy density of 17.276 Wh kg-1 at a power density of 207.3 W kg-1 in a wide potential window of 1.5 V. Such intriguing capacitive behavior is attributed to the abundant porous structures in the hexagonal nanoplates.A hierarchical porous birnessite-type MnO2/C microsphere was synthesized by a high temperature solid state method and galvanostatic charge-discharge. It exhibits a high area normalized specific capacitance and excellent cycle stability.This remarkably enhanced electrochemical performance isascribed to the following structural features of the electrode. The mesoporous nature ensured the interaction between the electrolyte and the inner materials; The highly graphitized carbon strips dispersing in the manganese oxide formed an electric carbon network forenhancing the electron conductivity of birnessite-type MnO2; The electric carbon network also strengthened the structure and accelerated the transfer of the low valence manganese oxide to an electrochemical active MnO2, thereby, increased the electrochemical stability. This work also revealed the important role of carbon in the structure change of birnessite MnO2 and their pseudocapacitive performance. The carbon materials in manganese oxide exhibited their distinctive features for pseudocapacitors. Because of excellent mechanical properties and superior conductivity, the carbon strips not only act as the active sites for the transformation of manganese oxide, but also maintain the mechanical integrity and high electrical conductivity of the electrode materials. Thus, the electrochemical performance of the MnO2/C remarkably increased.