Synthesis Of Metal Oxide Nanostructures And Study On Electrochemical Lithium Storage Properties

The demand for more and more clean energy is rising with the rapid development of industrial economy and the increasingly urgent environmental governance.Fossil fuels have been unable to meet the needs of society because of its serious pollution and non-regeneration.The development of clean and efficient new energy is the trend of the times,has long been the focus of attention.Lithium ion batteries have been widely used in a variety of small electronic equipment and it has broad application prospects in the electric vehicle power supply and solar energy,wind energy and other renewable energy storage Electrode material is the key to the performance of lithium ion battery.The current commercial graphite materials have low theoretical capacity and security issues.Therefore,it is urgent to develop new anode materials with high energy and high stability.Transition metal oxides have the advantages of high capacity,excellent cycle performance and high safety performance.So that,the transition metal oxide is a kind of ideal anode material instead of graphite.However,the problems of transition metal oxides,such as poor conductivity,large irreversible capacity and large volume change before and after charging and discharging,greatly limit the practical application of transition metal oxides.The results show that the nano structure,the morphology control and the carbon coating can effectively improve the conductivity of the material,alleviate the volume expansion during charging and discharging,and improve the electrochemical performance of the material.In addition,hydrogen as another kind of clean energy has received a universal attention.How to efficiently produce hydrogen from water is one of the current research hot spots.The electro-catalytic hydrogen evolution reaction is considered to be an efficient way to produce hydrogen Precious metals are used as catalysts for the catalytic hydrogen evolution reaction.However,the precious metals are expensive and lack of reserves,so it is urgent to find an efficient and economical catalyst.Transition metal sulfides can be used as an efficient hydrogen evolution catalyst to replace conventional noble metal catalysts.But how to further improve the catalytic activity of transition metal sulfides is still a limiting factor.It has been found that the transition metal sulfide nanostructures synthesized with special morphologies or doping with other materials can effectively improve the catalytic activity.In this paper,transition metal oxides and transition metal sulfides were prepared by hydrothermal method.The technology such as X-ray diffraction?XRD?,scanning electron microscopy?SEM?and transmission electron microscopy?TEM?were used to analyze the physical characteristics and structure of the materials.The electrochemical properties of the materials were tested by constant current charging and discharging,cyclic voltammetry?CV?and electrochemical impedance spectroscopy?EIS?.The relationship between the structure and morphology of the materials and the electrochemical properties of the materials was analyzed.The main research contents and results are as follows:?1?The silicon dioxide coating layer is formed on the surface of the precursor FeOOH.Under the protection of the silicon dioxide coating layer,the iron oxide material can keep the one-dimensional nanostructure of the precursor.During the calcination process,the precursor FeOOH is converted to iron oxide,and dehydration occurs simultaneously to form a porous structure on the surface of the materials.This unique porous one-dimensional nanostructure is beneficial to the intercalation and release of lithium ions and the rapid migration of electrons.At the same time,the surface pores can effectively relieve the volume change of the electrode during charging and discharging,and improve the stability of the cycle.?2?The hollow nanostructures assembled by Co MoO₄ nanosheets were prepared by using a simple way to construct ultra-thin CoMoO₄ nanosheets on the surface of silica oxides at the same time etching the core silica dioxide template.The radial vertical lamellar structure can provide more positions for the insertion of lithium ions,and the internal hollow structure can effectively alleviate the volume effect of the materials,so that the material has a good lithium storage performance.At the current density of 500 mA·g-1,a high discharge capacity of 1066 mAh·g-1 is retained even after 200 cycles.The capacity retention rate was 93 % and the columbic efficiency was 98 %.Because of the special structure of the material and the large surface area,the actual capacity is higher than the theoretical capacity of CoMoO₄.Even at a very high current density of 10 A·g-1,a high reversible capacity of 470 mAh·g-1 could still be achieved,which is much higher than the theoretical capacity of 372 mAh·g-1 for graphite.The results show that the material has good rate performance and cycle stability.?3?The Fe₃O₄@MoS₂ heterostructured material was synthesized by coating the molybdenum disulfide nanosheets on the surface of the iron oxide nanometer sphere template.And the Fe₃O₄@MoS₂ heterostructured material as a catalyst for the electrocatalytic hydrogen evolution reaction.It has been proved that the Fe₃O₄@MoS₂ material with this special structure has better hydrogen evolution performance than hollow molybdenum disulfide.The calculated results show that the electrocatalytic activity of the material is twice that of the hollow molybdenum disulfide and the catalytic activity of the active site on the unit area of the material is improved by the addition of ferric oxide.