Sdesign,Synthesis And Electrochemical Properties Of Metal-Air Battery Electrode Materials

With the rapid development of modern society,oil and other nonrenewable energy are increasingly consumed.The energy and environmental problems are becoming increasingly prominent.The development of new energy storage systems and energy conversion systems with high performance,green and environmental protection has become the focus of people’s attention.Among them,finding new energy storage and conversion materials has become one of the most challenging tasks.Recently,the metal-air battery has attracted people’s attention because of its ultra-high energy density.It has become a new energy system that is expected to develop on a large scale after lithium-ion batteries.The key to develope of metal-air batteries lies in the preparation of cathode catalyst materials.This paper focuses on the preparation and synthesis of metal-air electrode materials,and systematically studies the electrochemical properties of the prepared electrode materials.Combined with various analytical methods and first principles caculation,the internal mechanism of the high catalytic activity of the materials is calculated and analyzed.As the most commonly used substrate material for metal-air batteries,carbon materials often have the disadvantage of low catalytic activity.Among them,the carbon cloth material has both flexibility and air permeability,allowing the gas component of the positive electrode to pass through and participate in the battery reaction smoothly.However,the catalytic activity of the original carbon cloth is poor,and it is not directly used as an electrode of a metal-air cell,but as a base material combined with other materials to form a composite material.Here we start by improving the inertness of the original carbon cloth.A series of studies have been carried out on the joule heat treatment of the original carbon cloth,the combination of the original carbon cloth and metal oxide,the carbon cloth supporting heteroatom-doped manganese oxide,and the construction of three-dimensional porous carbon supporting heterojunction of metal/metal carbide.In the third chapter of this thesis,in order to improve the chemical inertness of the original carbon cloth,we use the joule heat principle to treat the original carbon cloth material,and by adjusting the appropriate current and processing time,a porous carbon cloth（Porous CC）material with a hierarchical porous structure is obtained to improve.Then,using the lithium affinity of the processed porous carbon cloth,an experiment of immersing molten lithium in an atmosphere containing a small amount of nitrogen was performed.During the process of impregnating molten lithium,hexagonal Li₃N was formed in situ on the carbon cloth,and finally the Porous CC/Li₃N composite negative electrode material was obtained.The lithium-oxygen full battery assembled with Porous CC/Li₃N composite anode material and porous carbon cloth also has excellent cycle performance.In the fourth chapter,the catalytic activity of the original carbon cloth and metal oxide composite material is studied.In the previous chapter,we learned that the catalytic activity of the original pure carbon cloth is very poor,so this chapter uses manganese oxide with high catalytic activity to compound with the carbon cloth substrate,which uses both the porosity of the carbon cloth and the catalytic activity of metal oxide.In general,this chapter uses hydrothermal synthesis to reduce the temperature required for the reaction.Through simple hydrothermal reaction and adjusting different temperatures,composite catalyst materials with different crystalline Mn O₂ loaded on carbon cloth are prepared.By introducing Mn O₂ as a catalyst,the feasibility of a rechargeable Na-N₂battery at room temperature was proposed and proved for the first time.In chapter 5,based on the previous chapter,we know that although pure metal oxides have catalytic activity,their long-term cycle stability needs to be improved.Therefore,from the perspective of improving the long-term stability of oxides,we use microwave assistance synthesis method successfully prepared a carbon cloth-supported Co element-dopedα-Mn O₂ nanowire(Co_xMn_1-xO₂/CC)composite electrode material.The use of microwave synthesis has the characteristics of rapid and efficient.We prepared Co_xMn_1-xO₂/CC composite electrode materials in a short time.By adjusting the different doping ratios,we optimized the best Co doping amount to 0.2.The lithium-carbon dioxide（Li-CO₂）battery was assembled with this optimized Co_0.2Mn_0.8O₂/CC composite electrode material.The possible doping sites and the influence of element doping on the electronic structure and band structure of Mn O₂ were calculated and analyzed using first-principles.The excellent electrochemical performance was mainly related to high conductivity,enhanced specific surface area and unique gap doping.In chapter 6,based on the previous chapters,we learned that although the modification of metal oxides and their derivatives can improve the catalytic activity and long-cycle performance of carbon-based composites,but the improvement of electrode polarization is not obviou.In this chapter,a 3D honeycomb graphene-supported metal/metal carbide heterojunction（3DHG-Mo/Mo₂C）composite was designed and synthesized using the method of constructing metal/metal carbide heterojunction.XRD,SEM,TEM and other component analysis methods are used to analyze the heterojunction structure.Electrochemical tests show that the composite material containing heterojunction has excellent catalytic activity,ultra-low overpotentialand high cycle stability.