Preparation And Lithium Storage Properties Of Silicon/Crbon(Graphene) Composite Anode With Ordered Mesoporous Silica As Template

The advancement of science and technology has facilitated human life.However,the growing demand for energy has also spawned a series of problems such as the depletion of fossil energy and the deterioration of the natural environment.Lithium-ion batteries have become a vital energy storage technology for the new energy industry due to their high energy density and safety.Among many lithium-ion battery anode materials,silicon has attracted a lot of attention with its high theoretical specific capacity.However,intense lithium intercalation expansion and insufficient electrical conductivity have become the main obstacles in the practical application of silicon-based anodes.In order to suppress volume expansion and improve conductivity,this paper designed and synthesized a variety of porous silicon anodes.On this basis,porous silicon and graphene,pyrolytic carbon composite anode materials were prepared.(1)With TEOS as the silicon source,the ordered mesoporous silica in the shape of rod,sphere and cube(r-OMSiO2,s-OMSiO2 and c-OMSiO2)were synthesized by adjusting the type of surfactant and the amount of raw material.Then,the porous silicon anode materials(r-PSi,s-PSi and c-PSi)were obtained by magnesiothermic reduction.The products have abundant porous structure,which can reserve buffer space for volume expansion,thus showing much better electrochemical performances than nano-silicon.After 100 cycles at a current density of 100 mA·g-1,the specific capacities of r-PSi,s-PSi and c-PSi remained at 346.8 mAh·g-1,526.8 mAh·g-1 and 461.5 mAh·g-1,respectively.(2)After the amination modification,the r-PSi,s-PSi and c-PSi were compounded with GO.Finally,r-PSi/rGO,s-PSi/rGO and c-PSi/rGO composite anode materials were obtained through high-temperature reduction.The porous silicon particles were distributed on the folded graphene sheets,showing good composite structures.Compared with pure porous silicon anodes,the electrochemical properties of PSi/rGO composite anode materials are significantly improved,mainly due to the conductive network provided by graphene and its buffer against volume change.After 100 cycles at a current density of 100 mA·g-1,the specific capacities of r-PSi/rGO,s-PSi/rGO and c-PSi/rGO composite anodes can maintain at 996.1 mAh·g-1,1088.8 mAh·g-1 and 738.2 mAh·g-1,respectively.(3)The self-polymerization reaction of dopamine in the Tris-HCl buffer system was used to coat the surface of r-PSi,s-PSi and c-PSi with polydopamine.After pyrolysis at high temperature,the r-PSi/C,s-PSi/C and c-PSi/C composite anode materials were obtained.All of them present a clear core-shell structure,and the lithium storage properties have been greatly improved compared with that before carbon coating.After 100 cycles at a current density of 100mA·g-1,the specific capacities of r-PSi/C,s-PSi/C and c-PSi/C composite anodes can maintain at 1418.4 mAh·g-1,1751.7 mAh·g-1 and 1070.5 mAh·g-1,respectively,indicating that the nitrogen-doped carbon layer could significantly improve the electrochemical stability.