Fabrication And Application Of Sio/graphit Composites Anode Materials For Lithium-Ion Battery

Silicon has a high theoretical capacity(4200 mAh g-1)and high natural abundance,non-toxicity.It is the most promising material being the next generation anode materials for lithium-ion battery.However,the volume expansion(300%)of silicon is huge in the charge-discharge process,and its conductivity is low,which leads to the crushing of active material particles and the continuous growth of the SEI film,which affects the cycle stability and service life of the material.Compared with Si,SiO2 has a smaller volume expansion ratio(150%)?it can improve the above problems by recombining with carbon.In this dissertation,based on the fact that SiO has low volume expansion rate,good cycle stability,and low first Coulomb efficiency,it is compounded with graphite by ball milling,spray drying and other methods to prepare SiO/C composite anode materials with high tap density material.The main research contents and conclusions are as follows:(1)With SiO as the silicon source,it is uniformly mixed with graphite and organic additives and broken by ball milling.Using spray drying techniques,the resulting mixture was spray-granulated to give a SiO/graphite/C composite.In order to further improve its first coulombic efficiency and tap density,it was vapor-phase carbon-coated to obtain SiO/C composite microspheres.Through the optimization of the additive,SiO/C ratio,and the carbon-bearing method during the preparation process,it was determined that when the additive is 3 g PVP,1.5 g glucose and 0.5 g CMC,the ratio of SiO/C is 1:2,and the carbon is packaged.Carbon nanotubes for CVD were coated with 20 sccm of acetylene gas for 15 min to obtain negative electrode materials with excellent electrochemical performance.The tap density of this material is 0.80 g cm-3,its initial reversible specific capacity is 701 mAh g-1,the reversible specific capacity is 627 mAh g-1 after 300 cycles at 0.2 A g-1 current density,and the capacity retention rate is 89.3%.(2)The SiO and graphite were broken into nano-poles by sanding and mixed well,and then they were granulated by mechanical compacting to obtain SiO/C composites with higher tap density.Then,the characteristics of Si can be obtained by disproportionation of SiO,and the SiO/C composite material is disproportionated at high temperature to obtain a Si/SiO/C composite negative electrode material.Through the optimization of the sanding time,disproportionation temperature and time,it was determined that when the sanding time is 2 h,the disproportionation temperature and time are 950 ? and 3 h respectively,the material has excellent electrochemical performance.The material has a tap density of 0.84 g cm-3,an initial reversible specific capacity of 686 mAh g-1,a reversible specific capacity of 633 mAh g-1 at a current density of 0.2 A g-1 for 300 weeks,and a capacity retention rate of 92.35%.