Preparation And Lithium Storage Performance Of Silicon Anode Materials For Lithium Ion Batteries

Silicon-based anode materials have attracted widespread attention due to their high theoretical specific capacity(3579 mAh g^-1),high safety,environmental friendliness,and low price.They are considered the most promising anode materials for lithium-ion batteries.However,this kind of material will generate a huge volume expansion?>300%?during the process of lithiation and delithiation,leading to the fragmentation and differentiation of the material,resulting in poor cycling performance of the material.Therefore,it needs to be modified to improve the electrochemical performance of the naterial.The main research contents and results are as follows:?1?Si@rGO composites are prepared by using nano-silicon and graphite oxide prepared by improved Hummer?s method as raw materials,and using hydrothermal reduction-low temperature heat treatment.The effects of parameters such as hydrothermal reaction temperature,hydrothermal reaction time,PVP addition amount,and compound ratio on the properties of the material were studied.The test results show that when the hydrothermal reaction temperature is 160?,the hydrothermal reaction time is 10 h,and the mass ratio of silicon to graphite oxide is 1:2,the electrochemical performance of the composite is good.Under optimized conditions,the material?s first reversible specific capacity was 1195.6 mAh g^-1.After 50 cycles,the electrode reversible specific capacity was 864.6 mAh g^-1,and the capacity retention rate was 72.3%.When the current density is 2000 mA g^-1,the reversible specific capacity of the composite material is still as high as 911.1 mAh g^-1,and the rate performance is good.?2?Using silane to modify the surface of nano-silicon and discuss the performance of the coating method on Si@SiO_x composites,and prepare Si@SiO_x@rGO composites.The results show that the presence of silicon oxide improves the interface stability of the material and effectively alleviates the volume change of silicon.Under optimized conditions,Si@SiO_x@rGO composites exhibit good electrochemical properties.The first reversible specific capacity was increased to 1432.2 mAh g^-1.After 50 cycles,the reversible specific capacity of the composite material was 1039.4 mAh g^-1,which had good cycle stability.The capacity has been significantly improved,and the cycle performance is better.The AC impedance test results show that the electrochemical transfer resistance of the material after silane modification is significantly reduced.?3?The sol-gel method was used to prepare the Si/TiO₂ composite material.The effect of compound ratio on the properties of materials was discussed.The electrochemical test results show that the Si/TiO₂ composite exhibits good electrochemical performance when the silicon content is 15%.Its first reversible specific capacity was 720.9 mAh g^-1.After 200 cycles,the reversible specific capacity of the composite material was 730.4 mAh g^-1,and the cycling performance was very stable.The TiO₂ skeleton is helpful to improve the stability of the material structure effectively alleviate the volume effect of silicon during the charge and discharge process,further improve the conductivity of the composite material,and enhance its rate performance.After cycling,the electrode surface is relatively flat,few cracks,and the electrode structure remains relatively intact.