The Application Of Silicon@Carbon Composites In High Performance Lithium-ion Batteries

At present,the most direct way to improve the endurance mileage of new energy vehicles is to select electrode materials with higher energy density.Anode materials are an important aspect affecting the performance of lithium-ion batteries,reasonable selection of anode materials with high energy density is the key to improving distance per charge.Silicon anode has a high theoretical capacity of 4200mAh g^-1 and is abundant in reserves,it has been extensively researched by scientific personnel.However,the poor electrical conductivity of silicon and the huge volume expansion?>300%?during lithiation/delithiation processes have seriously affected its performance;At the same time,nano-silicon are expensive due to the high cost of their preparation process,which also seriously hinders the commercials application of it as anode for lithium-ion batteries.Therefore,this paper mainly researched the preparation,characterization and lithium storage perf5ormance of Si/C composite nanomaterials,and reported a method for producing nano-silicon particles with low-cost,simple process and large scale production.The main contents are as follows:Preparing porous Si/C composite nanofibers,Firstly,nano-silicon particles,PAN and iron acetylacetonate are dissolved in DMF solution,and composite nanofibers of silicon/PAN/acetylacetonate are prepared by electrospinning,and then annealed to obtain composite nanofibers of silicon/carbon/iron oxide,at last,the porous Si/C composite nanofiber obtained by washing with acid.The graphitized carbon through PAN under the catalysis of iron oxide,which enhances the conductivity of the whole anode material.The pores provide a buffer space for the volume expansion of silicon,and solves the problem of materials pulverization with the graphitized carbon together.The flexible sheet structure avoids the introduction of conductors and binders,reduces the electrode polarization and increases the energy density.Finally,the porous Si/C composite nanofibers exhibit superior performance,the initial discharge capacity is as high as 4100 mAh g^-1 at a current density of 0.4 A g^-1,which is very close to the theoretical capacity of silicon and can be maintained at around 1900 mAh g^-1 after 100cycles.It can be achieved 700 mAh g^-1 after 500 cycles at a current density of 21 A g^-1.Preparing porous Si/C composite nanoparticles,firstly,fly ash was used as raw material to obtain nano-sized silica by ball milling at 300 r/min for 32 h.Then,silicon particles with the size of about 5 nm were obtained by magnesium thermal reduction and pickling,and then carbon coated with phenolic resin to obtain porous Si/C composite nanoparticles.The obtained porous Si/C composite nanoparticles were characterized by SEM,TEM,XRD,etc.Finally,testing its electrochemical performance.The results show that it has better cycle performance.The initial discharging capacity is about 2600 mAh g^-1,and the special capacity can stabilize at about 750 mAh g^-1 at 2.0 A g^-1 after 200 cycles.When current density up to 6.0 A g^-1,the reversible capacity is about 565 mAh g^-1.