Preparation Of Silicon Anode Materials For Lithium Ion Batteries From Corn Straw

With the popularity of mobile electronic devices and new energy vehicles,lithium-ion batteries are more and more widely used.Silicon anode,as a kind of anode material for lithium-ion batteries,has high theoretical specific capacity（4200m Ah/g）,so it has been widely studied.However,the volume expansion and the formation of SEI film in the process of repeated lithiation/delithiation hinder the realization of theoretical capacity.Reducing the size of materials and designing porous materials and morphologies are the main directions for the improvement of silicon anode.Straw is the most common crop in Northeast China,its yield is very high,but it is rarely used reasonably,and it will produce environmental pollution when burned.Silicon is rich in straw and exists in the form of silicate.In this paper,porous silicon-based materials were prepared by magnesium thermal reduction reaction using straw as biomaterial,and the excellent properties compared with commercial silicon were obtained.After studying the factors that may affect the properties of straw silicon materials,the effects of mass ratio of magnesium and silicon dioxide,the use of HF,reaction temperature,reaction time,heating rate and other factors on the morphology and electrochemical properties of magnesium thermal reduction products were investigated.The reasons for the change of the final product with the change of different reaction factors are described in detail:the mass ratio of magnesium to silica in magnesium thermal reduction affects the composition and purity of the final product;when the mass of magnesium is too low,the reaction can not be carried out completely,resulting in the uneven morphology of the material.When the mass of magnesium is too high,it will produce side reaction and affect the final morphology.The necessity of HF after Mg O thermal reaction and its effect on the morphology of the samples are explained.It is confirmed that the Si O₂after reaction does not exist in the form of Si O_x.It is found that the lower reaction time is not enough to make the reaction complete,and the longer reaction time will lead to the side reaction and the melting of the material at high temperature,resulting in the reduction of porosity.The heating rate has a great influence on the reaction degree and final properties of the samples.Too high heating rate will lead to insufficient reaction and decrease the crystallinity.When the temperature is too low,the boiling point of magnesium can not be reached,and the thermal reaction of magnesium can not be fully realized.If the temperature is too high,the side reaction will increase and the crystallinity of silicon will decrease.Using straw as raw material to prepare silicon not only has low cost and safety,but also realizes the reuse of biomass and reduces environmental pollution.Finally,the excellent straw silicon material with first discharge capacity of 3692.8 m Ah/g,100cycle capacity of 1573 m Ah/g,specific surface area of 72.08 m²/g and average pore size of 14.21 nm was prepared.