Design,Construction And Electrochemical Performance Of Tin-based Electrotrode Materials

With the increase of the world population and development of society,the demand of energy is dramatically increased,thus leading to the excessive consumption of fossil energy,which brings the severe environment pollution such as the air pollution.The development of electrochemical energy conversion and storage devices has shed light on the rational utilization of renewable energy such as the tidal power and reduction of the use of fossil energy.Among them,lithium ion batteries have been widely used since successfully commercialized because of the advantages of high energy density,high safety and long life.However,the lack of lithium resources and the rising prices of raw lithium material limit its large-scale application.Therefore,development of low-cost and high-performance electrochemical energy conversion and storage devices seem to be very necessary.Sodium ion batteries are seen as ideal substitute for lithium ion battery and have attracted much attention due to its abundant resources in the earth's crust,cheap prices and similar physical and chemical properties to lithium.Electrode is a key component of a battery.So developing the electrode material with high performance is of great significance for the large-scale application of lithium/sodium ion batteries.Among them,the tin-based electrode materials are widely studied for the rich resources,low cost and high theoretical capacity.While the volume change during cycling of the material is large,leading to material pulverization and sharp drop in electrochemical performance.To solve the problems mentioned above,in this thesis,from the perspective of improving the electrical conductivity,the structural stability and optimizing the electrochemical performance of tin-based electrode materials,carbon-confined mesporous SnO₂@NC nanocubes and yolk-shell CoSn@NC nanoparticles were designed and constructed by chelation-etching and redox reaction methods,respectively.The application of SnO₂@C and yolk-shell CoSn@C in LIBs and NIBs were investigated respectively.The main research results are as follows:?1?Carbon-confined mesporous SnO₂@C nanocubes with varied specific surface area and pore diameter were synthesized via chelation-etching method using EDTA as chelation-etching agent and CoSn?OH?₆ as the raw material.When chelation-etching agent ratio rises gradually,EDTA is first to chelate cobalt,then tin.And the specific surface area and pore diameter increase synchronously.?2?When the proportion of reactants and chelation-etching agent is 1:1.2,the product possesses the best electrochemical performance.When tested as an anode for SIBs,it delivers a reversible capacity of 255 mA h g^-1 at the current density of 1000mA g^-1 after 1000 cycles,with a capacity retention of 84.5%.The average discharge capacities of 210 and 185 mA h g^-1 can be obtained at the current densities of 2 and 5A g^-1 respectively,indicating the outstanding rate capability.When used as an anode for LIBs,it delivers a reversible capacity of 1070 mA h g^-1 at the current density of1000 mA g^-1 after 200 cycles,with a capacity retention of 87%.The average discharge capacities of 920 and 590 mA h g^-1 can be obtained at the current densities of 2 and 5A g^-1 respectively.The excellent electrochemical properties of the material are attributed to the rational design of carbon-confined mesoporous structure.The unique structure can shorten the ion diffusion path and the space between inner particles can effectively reduce the volume variation during cycling.Besides,the outer carbon layer can inhibit the agglomeration and pulverization of the active material and ensure the structural stability of the active material.?3?The pure phase of yolk-shell CoSn@C nanoparticles were obtained via the method of redox reaction using dopamine as the carbon resource and reducing agent at700?under the nitrogen atmosphere.?4?When tested as an anode for LIBs,it delivers a reversible capacity of 350 mA h g^-1 at the current density of 1000 mA g^-1 after 800 cycles and the average discharge capacities of 421 and 339 mA h g^-1 can be obtained at the current densities of 2 and 5A g^-1 respectively,demonstrating the excellent cycling and rate capability.The prominent electrochemical performance of the material can be ascribed to the rational design of the yolk-shell structure.The unique structure can shorten the ion diffusion path and the space between the yolk and the shell can effectively reduce the volume variation during cycling,while the carbon shell can inhibit the agglomeration and pulverization of the active material and ensure the structural stability of the active material.Also the cobalt,which is non-electrochemical active,can serve as the conductive frame and improve the conuctivity of the active material.