Studies On The Electrochemical Energy-storage Performance Of Iron Phosphide And Manganese Dioxide Based Composite

As two typical electrochemical energy storage devices,lithium-ion and sodium-ion batteries have the advantages of almost no pollution,small volume and low maintenance cost.In order to meet the growing demand for energy storage,it is necessary to explore the advanced anode materials to improve the overall battery performance.This thesis mainly studies the energy storage of transitional metal phosphides and oxides,as well as improving the sodium-ion diffusion coefficient and electronic conductivity through designing nanoarrayed architecture and constructing composite materials,thereby enhancing their electrochemical performance as anode materials in lithium-ion（LIBs）and sodium-ion batteries（SIBs）.The iron phosphide（FeP）powders have a relatively low sodium-ion diffusion coefficient(¹0^-13 cm² s^-1)and a large volume change（>202%）during the process of storing sodium ions.In response to these problems,we design FeP nanorod arrays grown in situ onto Ti plates（FeP NRs/Ti）.The nanorod-array design helps the sodium-ion diffusion coefficient of FeP to reach¹0^-12 cm² s^-1,which is an order of magnitude higher than that of FeP powders coated on copper foils.FeP NRs/Ti delivers a reversible capacity of 196.2mAh g^-1 at a current density of 2 A g^-1（tested in the sodium-ion half-cells）.Besides,the close chemical interaction between FeP and Ti plates is helpful to maintain the morphology of the material,thus ensuring the electrode cycling stability.In addition,an energy system assembled by a Na₃V₂（PO₄）₃-FeP NRs/Ti sodium-ion full cell and perovskite solar cells achieves the photoelectric conversion and storage efficiency of 5.2%under standard illumination conditions（This efficiency is at a medium level in the analogous works such as a perovskite solar cell-lithium ion battery system,a dye-sensitized solar cell-lithium ion battery system,and the like）.This may be helpful to the further research on the application of sodium-ion batteries in the renewable energy storage field.The electronic conductivity of MnO₂ is relatively low(10^-3-10^-4 S m^-1).In response to this problem,we combine MnO₂ with nitrogen-doped carbon nanotubes（NCNTs）and find that the electronic conductivity of MnO₂/NCNTs composites is two orders of magnitude higher than that of pure MnO₂.Therefore,MnO₂/NCNTs exhibites better lithium-ion and sodium-ion storage capacity than pure MnO₂.Besides,in order to increase the intrinsic electronic conductivity of the n-type semiconductor MnO₂,we attempt to improve the carrier concentration of MnO₂ by introducing oxygen vacancies through the hydrogenation process.