The Research On Silicon And Carbon Core Shell Porous Composite Materials As Anode Material For Lithium Ion Batteries

With the rapid development of science and technology,there is a growing demand for lithium-ion batteries with high energy density in society.At this stage,silicon materials is considered as the most promising anode materials,due to its high theoretical capacity(3500 mAh/g)and lower charge-discharge potential.However,due to the non-conductivity of the silicon material,large volumetric expansion(370%)occurs after reacting with lithium ions,resu lting in that the battery can not reach the theoretical capacity and the capacity will drop drastically after multiple charging and discharging.Researchers all over the world have done a lot of researches on the negative electrode of silicon material as a lithium ion battery.The preparation of composite nano-silicon materials and shell-core porous Si@C composite materials are a solution to many problems of silicon materials.However,most of the researches have problems such as complex process,expensive raw materials and un-batch preparation.As a result,the research of silicon material as negative electrode of lithium-ion battery can not be applied to large-scale production well.The purpose of this project is to explore a simple,non-polluting,batch preparation method for the preparation of Si-C core-shell porous materials as lithium-ion battery cathode.The topic selected size between 100-300 nm of silicon nanoparticles as raw material,selection of common iron,nickel,calcium compounds as a template,choose cheap phenolic resin as a carbon source and dilute hydrochloric acid as an etchant to prepare Si-C core shell porous composite material.The subject proposed using fixed-speed precipitation method so that nano-sacrificial layer coated on the surface of the raw materi al.The principle is heterogeneous nucleation better than homogeneous nucleation,and confirm the feasibility of the experiment.The effects of graphene and phenolic resin as carbon source are studied respectively to prepare the porous carbon-silicon composite material.In the research of making sacrificial layer based on nickel-based materials,the subject uses the precipitation method to coat the nickel-based compounds and the freeze-dried method to coat graphene.Explores the graphene and phenolic resin as the carbon source respectively to prepare the porous carbon-silicon composite material.After many explorations,it is proposed that the precipitation be coated on the surface of the silicon particles by controlling the precipitation rate.The feasibility of the experiment is confirmed by SEM and TEM,the nickel compound is deposited on the silicon surface.After the phenolic resin pyrolysis and hydrochloric acid corrosion can be obtained carbon silicon shell nuclear porous structure.The results show that the material has excellent electrochemical performance,and the specific discharge capacity is maintained at 1002.2 mAh/g after 100 cycles of cycling at a high current density of 500 m A/g with a carbon content of about 50%.In the research of making sacrificial layer based on iron-based materials,this topic attempts ball milling,chemical precipitation and other methods so that iron compounds coated on the surface of silicon nanoparticles.For the first time,it is found that using ferrous iron as iron source and fixed speed precipitation method,the material will be self-oxidation and then formation of a special three-dimensional lamellar petal Bernalite ferric hydroxide.After carbon-coated and acid-treated,three-dimensional lamellar petal carbon-coated silicon particles can be formed.The method has advantages of cheap raw materials and simple operation.The structure can improve the conductivity of the composite material,reduce the transmission distance of lithium ions and slow the volume expansion effect of the silicon material.The material in the carbon content of about 50%,after 200 cycles,the discharge capacity can still be maintai ned at 1008 mAh / g.In the study of sacrificial layers made of calcium carbonate material,select alcohol as a solvent,choose alcohol-insoluble materials as reactants,take full advantage of heterogenous nucleation is better than homogeneous nucleation principle,making calcium carbonate on the silicon surface to form a perfect coating.In addition,the effect of different sacrificial layer thickness and different carbon content on the properties of the material is explored.It is found that two types of calcium carbonate crystal forms with the increase of calcium content.In addition,as the carbon content decreases,the specific charge-discharge capacity of the material will gradually increase,but the capacity decay rate will gradually increase.When the carbon content is about 80%,the first reversible capacity can reach 2200 mAh/g at 500 m A/g high current density,1600 mAh/g after 100 cycles,and 1100 after 300 cycles mAh/g.The experimental technology explored in this paper has the advantages of cheap raw materials,easy operation and mass preparation.Successfully prepared carbon silicon shell nuclear porous structure,and it has excellent electrochemical properties.The specific capacity of the material is much higher than the commercial graphite material(300 mAh/g).