Preparation And Electrochemical Properties Of Silicon-based Anode Materials Derived From Rice Husk

With the rapid development of society and the improvement of consumption levels,people's demand for energy is increasing,and the development of sustainable new energy becomes particularly important.Among them,lithium ion batteries(LIBs)have been widely concerned for its excellent performance.As an important part of lithium-ion batteries,anode materials play a vital role in the performance,safety and price of LIBs.Up to now,among the many electrode materials that people have proposed that may replace market-oriented graphite,silicon-based materials have the advantages of 4200m Ah g^-1 discharge capacity,safer discharge platforms than graphite,and amazing reserves in nature.It stands out among many candidate electrode materials.However,during the repeated deintercalation of lithium ions,the volume expansion of silicon based materials is obvious,and the new electrolyte boundary film(SEI)is repeatedly generated,resulting in serious electrode powder and obvious decrease in battery capacity.This has seriously restricted the pace of its commercialization.In addition,the current preparation process of silicon materials is complicated,and the production cost is high,which is not conducive to its commercialization.Aiming at the current scientific problems that need to be solved urgently,in this thesis,we used rice husk,an agricultural and sideline product rich in silicon,as the raw material,and used its natural biomass structure to synthesize silicon-based composite anode materials with rich pore structure through simple carbonization or aluminothermic reduction:(1)Using agricultural by-product rice husk as the silicon source,the precursor is first obtained by simple calcination,and then the precursor is ground and compounded with different proportions of graphite,and then undergoes carbothermal reduction at a certain temperature to synthesize a cheap and high-performance Porous silicon oxygen carbon(SiO_x/C@graphite,RH-XG)composite anode material.The composite material was characterized by XRD,TG,XPS,BET,EDS,SEM,and Raman,and its electrochemical performance was demonstrated by testing the assembled button half-cell.When porous SiO_x/C@graphite is used as the anode material of lithium ion battery,the battery exhibits excellent electrochemical performance.Among them,the RH-3G material still maintains a high discharge capacity of 834.9 m Ah g^-1 after being cycled for 200 cycles at a current density of 200 m A g^-1.Even at different current densities,it shows excellent rate performance.After 500 cycles with a current density of 500 m A g^-1,the porous SiO_x/C@graphite composite anode material still shows a discharge capacity of 500.4 m Ahg^-1.This is mainly because the porous structure provides a convenient channel for the transmission of lithium ions and reduces the consumption of active lithium ions.The addition of an appropriate amount of graphite on the one hand increases the conductivity of the composite material,on the other hand,it plays an important role in alleviating the change in silicon volume during the repeated deintercalation of lithium ions.In addition,the synergistic effect of the added graphite and the carbon matrix network formed in situ can further effectively improve the lithium storage performance of the composite material.(2)Using aluminum powder as a reducing agent and rice husk as a silicon source,graphite and pitch are used as conductive agents to prepare porous silicon/silicon oxide/carbon composite anode materials(Si/SiO_x/C@pitch and Si/SiO_x/C@Graphite(SCA-X).The physical properties of the composite material were characterized by SEM,XRD,BET and XPS.And the composite material was used as the negative electrode of lithium ion battery for electrochemical performance test.The test results show that after 200 cycles,the SCA-3 electrode with pitch as the conductive agent maintains a specific capacity of812.8/819 m Ah g^-1,and the SCA-3 electrode exhibits an ultra-high discharge capacity(2537.7 m Ah g^-1),while the SCA-4 electrode material is made of silicon oxide mixed with high conductivity graphite after140 cycles at a current density of 0.2 A g^-1,the charge and discharge capacities are 665.5 m Ah g^-1 and683.5 m Ah g^-1,respectively,and the first discharge capacity is much smaller than that of SCA-3,Si/SiO_x/C@asphalt has higher specific capacity and excellent cycle stability than Si/SiO_x/C@graphite composite anode material,indicating that asphalt can better inhibit the volume change during the cycle as a conductive agent.The research results show that under the hydrogen/argon mixed atmosphere,it is more conducive to the reduction of silicon dioxide by aluminum powder and the reduction of silicon dioxide provides more sites for the storage of lithium ions.The addition of pitch can be used as Buffer material,on the other hand,molten asphalt can fill the pores in the material,so the specific surface area of the material is greatly reduced,so that the SEI film formed during the charge and discharge process of the material is also reduced,which effectively improves the cycle stability of the material.(3)In order to further improve the performance of the silicon-oxy-carbon composite anode material,nano-nickel is doped into the SiO_x/C material by ball milling.The SiO_x/C@Ni composite material prepared by this method greatly improves the conductivity due to its external combination of conductive nickel dispersion and carbon particle network cladding.The electrode prepared with this material has excellent electrochemical performance.After being cycled for 100 times at a current density of 500 m A g^-1,the SiO_x/C@Ni electrode still maintains a considerable specific capacity(711.0/688.3 m Ah g^-1).This is mainly because the addition of nano-nickel improves the conductivity of the composite material.Increase the influence of nickel doping on electrochemical performance.