Preparation And Electrochemical Performance Of Mn-based Oxide As Electrode Materials

In order to meet the demand of energy system for social development,people try to explore some devices to save energy.As the presentations of novel energy saving technology,lithium ion batteries and supercapacitors exhibit many advantages,such as high energy density,high power density and environmental friendliness.The choice for electrode materials plays an important role in the electrochemical performance and the transition metal oxide(TMOs)is regarded as the promising one because of their high theoretical capacities and their safety properties.Among the different TMOs,manganese-based(Mn-based)oxide materials are cheap and have large reserves,so they have become the attractive electrode materials.However,the large volume shrinkage and expansion during the charge and discharge processes and low conduction largely affect their application.To solve these problems,Mn-based oxide materials generally composite with carbon materials or are constructed into some unique structures,thus the conductivity and the capability of transiting ions will be improved.The main contents of this research can be concluded as follow:1.With the assistance of polyvinyl polyvinylpyrrolidone(PVP),manganese oxide(Mn3O4)octahedron has been successfully synthesized via hydrothermal process.PVP,as the surfacants,is considered as the important element for controlling the morphology and agglomeration of octahedrons.The carbon coating manganese monoxide octahedrons are synthesized by carbonizing Mn3O4 via pyrrole.As the electrode of lithium-ion batteries,MnO@C shows great electrochemical performance.At the density of 100 mA g-1 the discharge capacity can reach 560 mA h g-1 after 80 cycles.When the current densities are improved to 200,400 and 800 mA g-1,it still remains 526,432 and 304 mAh g-1,respectively.Comparing with Mn3O4,the MnO@C exhibits better cycling performance are attribute to the presence of the carbon coating,and it is considered carbon layer could improve the electrical conductivity and as the buffer during the lithiation and delithiation processes.2.The porous orthohexagnal ZnMn2O4 is synthesized with dimethyl sulfoxide and ethanol as solvent via solvothermal process and annealing process.It is found the annealing temperature has a significant effect on the formation of structure and the degree of crystallinity.As electrode materials of lithium-ion batteries,porous orthohexagnal ZnMn2O4 shows good eletrochemical performance.At the current density of 100 mA g-1,the specific capacity can reach 716 mAh g-1 after 200 cycles and it also has a great rate capabilities.When it is used in supecapacitors,the specific capacity also can reach 340 F g-1 under the current density of 1 A g-1 after cycling 2000 times.The better eletrochemical performances have something to do with the porous structure,which is benefit for the reaction between the electrolyte and active materials.3.With the assistance of polyvinyl pyrrolidone(PVP),manganese molybdate(MnMoO4)rod with two-dimensional nanoflakes is synthesized via the thermostatic waterbath method.At the current density of 1 A g-1,the as-prepared MnMoO4 crystallines exhibits a high specific capacity of 109 C g"1 after 2000 cycles.With the improvement of current densities,the specific capacities still remain high values.The better performance of MnMoO4 rod owes to the two-dimensional nanoflakes structure,because they facilitate the contacting between active material and electrolyte and the diffusion of electrolyte.