Preparation And Electrochemical Performance Of Ceramic-coated SiO Anode

The actual specific capacity of commercial graphite anodes has gradually approached the theoretical specific capacity(372 m Ah g^-1),which cannot meet the increasing demand for high-energy density batteries.The silicon oxide anode has the advantages of high specific capacity(2600 m Ah g^-1),abundant resources,environmental friendliness,and low cost.It is one of the most promising anode materials.However,the silicon oxide will undergo significant volume expansion(?200%)during the process of lithiation/de-lithiation lithium,and it will also react with the electrolyte to form irreversible fluoride and consume the electrolyte,which will cause the silicon oxide electrode to fail and reduce the battery capacity.At present,The focus of research on silicon oxide anode materials is mainly on how to buffer the volume expansion that occurs in the process of lithiation/de-lithiation lithium,inhibit the side reactions that occur with the electrolyte,and improve the conductivity of silicon oxide.Therefore,in response to the above problems,this topic takes commercial silicon oxide anode materials as the research object,and prepares SiO@Ti N and SiO@CNTs@Ti N composites through fluidized bed chemical vapor deposition technology.The focus is on the preparation of titanium nitride coatings with different morphologies at different temperatures,and the growth mechanism of titanium nitride is explored on this basis.Two kinds of coated composites will be used as anode materials for lithium-ion batteries and their electrochemical performance tests will be carried out.The specific research content can be divided into the following three parts:(1)Using N₂-H₂-TiCl₄ as the reaction system,SiO@Ti N composite were prepared by fluidized bed chemical vapor deposition technology.After testing and analysis,it is found that three different morphologies(dot,film,island)of titanium nitride can be synthesized by controlling the temperature.From the analysis of thermodynamics and growth mechanism,the deposition law of titanium nitride ceramics is explored,and it is shown that when the temperature is lower(800?),the nucleation time of titanium nitride is longer,the growth time is shorter,and the morphology of titanium nitride is Point-like;as the temperature increases,the nucleation rate of titanium nitride increases,the nucleation time is shorter,and the growth time is longer,so the morphology of titanium nitride is film-like and island-like.When the temperature is 900?,a thin-film titanium nitride coating layer is obtained,and the preparation of the titanium nitride uniformly and completely coated silicon oxide composite is realized.(2)The electrochemical performance test of the cycle performance,rate performance and impedance performance of the composite formed by titanium nitride coated silicon oxide with three different morphologies:dot,film and island.After comparison,it is found that the complete film-like titanium nitride coated silicon oxide exhibits high lithium storage capacity and excellent cycling performance.The initial discharge and charge specific capacities of the composite are 1214.1 m Ah g^-1,respectively.After 100 times,the capacity retention rate was 84.36%,indicating that the complete titanium nitride coating can significantly improve the electrochemical performance of silicon oxide.(3)In order to further improve the transmission path of lithium ions and electrons,increase the intrinsic conductivity of silicon oxide,and promote the improvement of rate performance.The SiO@CNTs@Ti N composite material was prepared by two-step fluidized bed chemical vapor deposition technology.After the rate performance test,it is found that SiO@CNTs@Ti N-900?-30 min composite material obtained by the complete titanium nitride coating is 0.1 A g^-1,the discharge and charge specific capacities of the composite material are 1559.4 and 1033.9 m Ah g^-1;When the density is 2.0 A g^-1,the discharge and charge specific capacities are 476 and 462.3 m Ah g^-1;when the current density returns to 0.1 A g^-1,the discharge and charge specific capacities are 973.8 and 967.9 m Ah g^-1,The excellent rate performance is due to the conductive network formed by carbon nanotubes and the complete titanium nitride ceramic layer,which isolates the direct contact between the silicon oxide and the electrolyte,and inhibits the side reaction with the electrode material.