Preparation And Electrochemical Performances Of Silicon-based Composites Anode Materials For Lithium-ion Batteries

At present,lithium-ion battery anode materials are still dominated by graphite,while graphite anode materials have defects such as low specific capacity,poor structural stability,and poor rate performance,which seriously restrict the prospects for their further development.Therefore,the development of new,safe,low-cost and environmentally friendly lithium battery anode materials has become a research hotspot in the field of lithium-ion batteries.With its abundant resources,environmental friendliness,low discharge potential and high theoretical capacity,silicon is considered to be an ideal alternative to graphite anode materials.However,the low conductivity,slow diffusion rate of Li⁺,and large volume change of silicon anode materials greatly limit their practical application.In view of the many problems existing in silicon anode materials,this paper uses nano-silicon as raw materials to regulate its structure and properties by using a variety of ways,which better solves the above bottleneck problems and greatly improves the application prospects of silicon anode materials.The specific research is as follows:（1）Using glucose,dopamine,pyrrole and tannin as carbon sources,carbon-coated nano-silicon composite anode materials were prepared.Among them,the Si@DA（dopamine）silicon-carbon composite anode material with carbon content of 39.82%and carbon layer thickness of 5～10 nm showed high specific capacity,good rate performance and good cycle performance.At a current density of 0.5 A g^-1,it maintains an excellent specific capacity of1607.5 m Ah g^-1,and when the current density is increased to 1 A g^-1,it also has a high specific capacity of 1291.3 m Ah g^-1,and when the current density continues to increase to 4 A g^-1,it can also release a reversible specific capacity of 315.5 m Ah g^-1.At a current density of 1 A g^-1,460.8 m Ah g^-1remains in the specific capacity of 100 charge-discharge cycles.（2）Using silica powder with a particle size of 30 nm as raw material,an atmosphere tube furnace was used to introduce oxygen at high temperature to prepare Si@SiO_xmaterials,and the effects of coating thickness and structure on the electrochemical performance of nano-silicon composite anode materials at different temperatures were studied.Among them,the SiO_xlayer thickness of 5～6 nm Si@SiO_x800 silicon composite anode material showed high specific capacity,good rate performance and good cycle performance.At current densities of 0.5 A g^-1,1 A g^-1,2 A g^-1,4 A g^-1,the material maintains 3036.8 m Ah g^-1,2660.0m Ah g^-1,1978.1 m Ah g^-1,1309.2 m Ah g^-1.At a current density of 1 A g^-1,the specific capacity of 100 charge-discharge cycles leaves a very high specific capacity of 995.8m Ah g^-1.The effects of sodium alginate,polyvinylidene fluoride,polyacrylic acid and sodium-sodium styrene-butadiene butadiene rubber on the electrochemical properties of electrode materials were studied.Taking Si@SiO_x800-silicon composite anode materials as the research object,the electrode using SBR/CMC composite adhesive can effectively improve the cycle performance by passing SEM,rate test,long cycle test and AC impedance test.Under the current density of 1 A g^-1,the specific capacity of 100 charge-discharge cycles is 1239.9 m Ah g^-1,which is an extremely high specific capacity.