Preparation And Electrochemical Properties Of Silicon-carbon Composite Anode Materials Based On Diatomite

Silicon material with the highest theoretical specific capacity,is considered to be the most ideal anode materials,and has been received wide attention.At the same time,poor electrical conductivity and huge volume expansion during the process of charge and discharge are the main reasons that hinder its industrial application.Therefore,how to enhance the electrical conductivity of silicon materials and improve its volume expansion effect to improve circulation capacity,has become an important research topic in the field of silicon materials.In this paper,porous silicon nanoparticles with excellent properties were prepared by using diatomite as silicon precursor and changing magnesium thermal reduction conditions.Then silicon/amorphous carbon/graphite composites were prepared by a phenolic resin carbonization method,and the effect of graphite ratio on the physical and electrochemical properties of the composites,was investigated.Finally,cobalt sulfide modified silicon/amorphous carbon/graphite multicomponent composites were prepared and the effect of cobalt sulfide content on the physical and electrochemical properties of the modified materials was investigated.The experimental results are as follows:(1)when the mass ratio of magnesium powder to diatomite is 1:1.4,the temperature of magnesium thermal reduction is 680°C and the mass ratio of NaCl/diatomite is 2:1,porous silicon nanoparticles with average particle size of 50nm,specific surface area of 101.5732m~2/g and total pore volume of 0.3364cm~3/g,are obtained by magnesium thermal reduction of diatomite,and is used as the raw material for the preparation of silicon/carbon materials.(2)Silicon/amorphous carbon/graphite composites were prepared by carbonization of phenolic resin,silicon particles and graphite.When the mass ratio of silicon to phenolic resin is 1:1,the mass of graphite is 10%of the mass of silicon and the composite is calcined at 700°C in nitrogen atmosphere for 3 hours,the composite material with specific surface area of 320.11m~2/g,the first discharge capacity of1043.95mAh/g and the specific capacity after 200 cycles of 186.47mAh/g,was prepared.(3)Silicon/amorphous carbon/graphite multicomponent composites coated by cobalt sulfide,were prepared,and the amount of cobalt sulfide has an effect on the structure and electrochemical properties of the prepared materials.When the amount of cobalt sulfide is 10%wt,the initial discharge capacity of the composite is as high as1253.76mAh/g and the discharge capacity of 243.53mAh/g can still be maintained after 200 cycles.Cobalt sulfide during the process of charging and discharging involved in redox reaction of composite materials,which probably activated the material further to enhance the lithium ion transport rate,thus improving the electrochemical performance of Si/amorphous carbon/graphite composites.