Design And Synthesis Of Three-dimensional Transition Metal Compounds And Their Lithium/sodium Storage Propertie

The consumption of large amounts of fossil energy has caused irreversible pollution and damage to the human environment,so there is an urgent need for a new epoch-making energy revolution—replacing fossil energy with renewable energy to free mankind from the impending energy crisis and environmental disaster.In recent years,new energy technologies have been developed rapidly（including wind,solar,hydro and tidal energy and other renewable energy）,but due to time and space constraints,the new energy generation industry is still facing problems such as low utilization.Therefore,there is an urgent need to develop energy storage technologies with high efficiency and price advantages.Lithium-ion batteries（LIBs）have the advantages of high energy density,long cycle life,fast charging and discharging,etc.and have become the dominant power source for portable electronic devices,and are also one of the main development directions for future hybrid and electric vehicle power sources.However,the low theoretical lithium storage capacity of graphite anode for commercial lithium-ion batteries and the shortage of lithium resources have led to an urgent need to develop new anode materials with high capacity and new secondary batteries with low cost and green.Sodium ion batteries have a similar charging and discharging principle as lithium ion batteries and are more abundant in sodium compared to lithium,which makes them more suitable for future large-scale applications.However,sodium ions have a larger radius（1.02（?））compared to lithium ions（0.76（?））and therefore have slower migration kinetics.When graphite is used as an anode material for sodium ion batteries,it has poor electrochemical activity and low capacity.Therefore,the development of anode materials with high capacity,long cycle life and high multiplicity performance is the key to accelerate the development of lithium/sodium ion batteries.The main research of this paper is as follows:（1）In order to solve the problems of poor kinetics and solubility in electrolytes of polymetallic oxides（POM）based materials,a dual strategy of encapsulating conductive polypyrrole（PPy）and combining polyacids with MOF using nitrogen-containing ligands（1,10-phenanthroline monohydrate=1,10-phen）was adopted to effectively limit their solubility and improve their conductivity.That is,the inorganic-organic hybrid material,[Cu（1,10-phen）（H₂O）₂]₂[Mo₆O₂₀]（abbreviated as Cu-POMOF）,was successfully prepared by a one-step hydrothermal method using phosphomolybdic acid,1,10-phenanthroline monohydrate ligand and copper nitrate as raw materials.Then,the Cu-POMOF@PPy complex was obtained by coating PPy on its surface.When the composite was used as an anode material for LIBs,it exhibited good electrochemical performance,i.e.,a specific capacity of up to 769 m A hg^-1 after 160 cycles at a current density of 0.1 A g^-1 and good multiplicative performance(maintaining a specific capacity of 319 m Ah g^-1 after 500 cycles at a current density of 2 A g^-1).（2）The inherent properties of transition metal selenides and the differences in ionic radii and electronegativities among alkali metal ions lead to differences in their storage behaviors（including diffusion rates,reaction activation energies,adsorption sites,etc.）for Li⁺/Na⁺/K⁺,and the specific reasons for the differences are not clear.Based on this,the differences in the storage behaviors of ZnSe for Li⁺/Na⁺/K⁺were investigated by a combination of first-principles calculations and experiments.The results show that ZnSe has better Na⁺kinetics compared to Li⁺and K⁺.To further improve the Na⁺diffusion coefficient,cycling stability and multiplicative performance of ZnSe during cycling,we used a dual strategy of modulating the material microstructure and optimizing the electrolyte.On the one hand,three-dimensional ordered hierarchical pores（3DOHP）ZnSe heterostructures with nitrogen-doped carbon were designed and synthesized;on the other hand,the electrolyte was optimized to form a thin and stable SEI.sodium ion batteries composed of 3DOHP ZnSe@N,C heterostructures as the anode material and Na OTf/DIGYLME as the electrolyte showed excellent multiplicative performance and good cycling stability,i.e.,at After 800 cycles at a current density of 10 A g^-1,it still maintains a specific capacity of 241.6 m Ah g^-1.Meanwhile,the sodium storage mechanism of the 3DOHP ZnSe@N,C hybrid material was investigated by in situ XRD.Finally,the structure and composition of SEI were further investigated by ex-situ tests.（3）Metal sulfides are considered to be extremely promising anode materials for sodium ion batteries because of their high reversible capacity and fast reaction kinetics.In this paper,Indium sulfide nanoflowers were firstly prepared by one-step hydrothermal method and then coated with nitrogen-sulfur co-doped carbon material to obtain nano-flower-like In₂S₃@N/S-C complexes,in which the three-dimensional nano-flower-like structure can alleviate the volume expansion of indium sulfide in the process of sodium embedding and provide more active sites.The introduction of carbon with polar carbon-sulfur bonds also improved the underpressure failure of metal sulfide electrodes during cycling,and the S and N co-doped carbon significantly improved the reaction kinetics,enhanced the reversibility of electrochemical reactions,and improved the electrical conductivity of the composites.In addition,the effects of different electrolytes on the reaction kinetics of the materials were investigated by testing the sodium ion diffusion coefficient and apparent activation energy of the composites under different electrolytes.The results showed that the sodium ion battery assembled with ether-based（Na PF₆-DME）electrolyte presented a specific capacity of about 769 m Ah g^-1 after 800 cycles at the current density of 1 A g^-1.Moreover,the cells also exhibit excellent multiplicative performance,i.e.,they maintain a specific capacity of 370 m A hg^-1 after 800 cycles at a current density of 5 A g^-1.Finally,the sodium storage mechanism of In₂S₃@N/S-C composites was investigated using in-situ electrochemical impedance.