Synthesis Of Ordered Mesoporous SiO₂ And Preparation Of Si/SiC/C Composite Structure And Its Lithium Storage Performance

In recent years,most researchers of new energy materials have focused their attention on lithium-ion batteries.The exploration of anode materials for lithium ion batteries is an indispensable part.Silicon has attracted extensive attention from researchers due to its high theoretical specific capacity and moderate lithium ion deintercalation/intercalation potential.However,the rate performance and cycle stability of silicon materials are relatively poor,making it difficult to achieve commercial applications.When silicon material is used as the negative electrode of a lithium ion battery,there are two outstanding problems:?1?During the battery cycle,the silicon material undergoes volume shrinkage/expansion due to the deintercalation/intercalation of lithium ions,which leads to the destruction and collapse of the negative electrode material Moreover,the electrical contact with the current collector is lost,resulting in a low cycle stability of the battery.?2?The preparation cost of nanostruc-ture of silicon material is relatively high and it is difficult to produce on a large scale.In order to solve the above problems,this article synthesized the mesoporous silica structures?Si O₂-OMPs?using simple block copolymerization.Using Si O₂-OMPs as the precursor and the carbon-coated surface modification treatment,ordered mesopor-ous silica-coated carbon composite structures?Si O₂/C-OMPs?were prepared.Finally,an ordered mesoporous silicon-on-silicon-carbide-on-carbon composite structure?Si/Si C/C-OMPs?with good cycling performance was prepared by low-temperature magnesium thermal reduction reaction.The resulting composite nano-Si structure has a rich pore structure,which can alleviate the volume expansion and contraction effect of Si during battery charging and discharging,thus improving the cycle stability of the negative electrode material.At the same time,this simple and easy preparation method also improves the potential for large-scale industrial application of silicon-based anode materials.The main research results of this paper are as follows:?1?Using TEOS as a silicon source and P123 as a template agent,in a specific environment,Si O₂-OMPs particles with controllable sizes are synthesized.Conditions such as solution acid concentration and the addition of different dispersants can control the morphology of Si O₂-OMPs particles,and obtain short rod-shaped particles.?2?Si O₂-OMPs have a specific ordered mesopore structure.After carbon-coated surface modification treatment,the resulting Si O₂/C-OMPs can maintain the pore structure of the original template.The method of using dopamine as a carbon source to coat the surface with carbon to obtain a porous Si O₂/C composite structure has the characteristics of simple steps,uniform and even carbon coating,and good shape retention of the original material.?3?When Si O₂-OMPs are used for magnesium thermal reduction directly,the transformation sequence of the product phase is:Mg?Mg₂Si?Mg₂Si+Si?Si.The reaction process is divided into two steps:In the first step,the heated and evaporated Mg vapor diffuses to the Si O₂interface and reacts to form the intermediate phase Mg₂Si.In the second step,Mg₂Si reacts with unreduced Si O₂to transform into pure Si phase.?4?The carbon-coated Si O₂/C-OMPs composite structure undergoes a low-temperature magnesia reduction reaction to form a Si C layer between the inner Si and the outer C layer,resulting in a Si/Si C/C-OMPs composite structure.The Si C layer in this structure enhances the strength and stability of the material structure,making the cycle stability of the composite anode material greatly improved?compared to Si/C-OMPs?.The main innovations of this paper:?1?The acid concentration of the solution and whether different dispersants are added to control the morphology of the synthesized Si O₂-OMPs particles are prepared for the subsequent preparation of anode materials for lithium ion batteries.?2?Not only the Si/Si C/C-OMPs core-shell structure was prepared,but also the influence of the C-coating and the formation of the Si C layer on the interface stability and lithium storage performance of the lithium ion battery anode material.