Preparation,Carbon-coating And Electrochemical Performances Of Silicon Microparticles Anode Materials

Nano-sized and sub-micron-sized silica microparticles are an important basic raw material.They have the advantages of large specific surface area,small density,adjustable particle size,good dispersion,and chemical stability.They are widely used in biomedicine and optoelectronics,Catalysis,adsorption separation,engineering ceramics and many other fields.The reduction of silica microparticles into silicon-based materials for anode materials of lithium-ion batteries has become a new research hotspot in this field.At present,as the anode material of lithium-ion batteries,the volume effect(>300%)of silicon-based materials,the problem of pulverization during charging and discharging,and the continuous formation of new solid electrolyte interface(SEI)have severely restricted the use of the applications silicon-based materials in lithium-ion batteries.Based on a comprehensive discussion of the current research status of anode materials for silicon-based lithium-ion batteries,this paper simulated the hydrolysis and polymerization mechanism of methyl orthosilicate(TMOS),and uses TMOS and TEOS as the precursor to prepare them separately by a sol-gel method.Nano-silica porous microspheres were prepared using TMOS as precursors,and monodispersed silica microspheres were prepared using TEOS as precursors.The apparent morphology,particle size distribution and surface characteristics of the two silica microspheres were characterized.Based on this,Nano-silicon porous microspheres and silicon microsphere anode materials were prepared by magnesium thermal reduction method,and their microstructure and electrochemical properties were analyzed.Finally,amorphous carbon coating technology was used to prepare silicon-carbon composite microsphere anode materials respectively.Effect of coating on the electrochemical performance of silicon-based microsphere anode materials was researched.Through the nano-based materials of silicon-based materials,monodispersion,porosity,and carbon coating,it provides important references for the solution of the volume effects of silicon-based anode materials,the problem of chalking during charging and discharging,and the solid electrolyte interface(SEI).The main research contents are as follows:(1)Simulation calculation of hydrolysis dimerization of methyl orthosilicate(TMOS).Using the first-principles simulation of the hydrolysis and dimerization of methyl orthosilicate(TMOS),it is concluded that the degree of hydrolysis reaction of TMOS under acidic conditions is higher than that of neutral conditions;the reaction protonated TMOS reacts with water is better than the reaction of TMOS hydrolyze with hydrated hydrogen ions;the first two steps of TMOS molecule hydrolysis are carried out successively,and then the two steps of polymerization occur and then are controlled by the barriers of the three hydrolysis and the polymerization reaction of the three hydrolysates.The reaction rate of TMOS hydrolytic polycondensation reaction that was simulated is mainly limited by the polymerization of the third and third hydrolysis reactions.(2)Preparation,reduction of silica porous microparticles and carbon coating of silicon porous microparticles.Silica porous particles were prepared by TMOS hydrolysis.By exploring a controllable preparation scheme,porous silica particles with a specific surface area of 307.03 m~2/g was prepared.After magnesium thermal reduction,the specific charge and discharge capacity of the porous silicon particles were1037 mAh/g and 606.7 mAh/g,and 88.7 mAh/g after 80 turns.The prepared silicon microspheres were coated with different concentrations of carbon by hydrothermal method.The carbon-coated silicon porous particles prepared in a 0.25M glucose solution had the best performance.The first-cycle discharge and charge specific capacity was 956.6 mAh/g and 578.4 mAh/g with 60.46%Coulomb efficiency at the first lap and a stable specific capacity of 364.3 mAh/g after 80 laps(3)Preparation,reduction of monodisperse silica porous microspheres and carbon coating of monodisperse silicon porous microspheres.Silica monodisperse microspheres were prepared by TEOS hydrolysis.Through exploring the controllable preparation scheme,silicon monodisperse microspheres with a particle diameter of about 500nm were prepared.After magnesium thermal reduction,the discharge and charge specific capacity of the first circle of silicon microspheres It is 1403.6 mAh/g and 636.4 mAh/g,and 280 mAh/g after 80 cycles.The prepared silicon microspheres were coated with different concentrations of carbon by hydrothermal method.The carbon-coated silicon microspheres prepared in 0.5 M glucose solution had the best performance.The first-cycle discharge and charge specific capacity was 927.8 mAh/g and 528.0 mAh/g,with 56.91%Coulomb efficiency on the first lap and a stable specific capacity of 462.9 mAh/g after 80 laps.