Research On Structure Evolution Law Of Silicon-based Material Electrode Ion Doping Process

Lithium-ion batteries are “green energy” among many chemical power sources,and have great application potential in the fields of electric vehicles and energy storage technologies.However,the research on large-capacity lithium-ion batteries at this stage is not yet mature,mainly due to the current low theoretical capacity of graphite anode materials.Silicon has the advantages of high theoretical mass specific capacity(more than ten times that of traditional graphite anodes),abundant reserves,and low cost.It is considered to be one of the most promising new-generation large-capacity lithiumion battery anode materials.However,the insertion of lithium ions during the charge and discharge process of the silicon electrode will cause significant volume expansion.After multiple charge and discharge cycles,the interior of the silicon electrode material is prone to chipping and even powdering,which limits the application of silicon anode materials.This paper uses first-principles methods to study the intercalation process of lithium atoms at different doping sites and different concentrations in silicon materials,and analyzes the stability,structural changes,band structure,and density of states of lithium atoms at different doping sites,in an attempt to reveal the volume expansion mechanism of the silicon anode material during lithium intercalation.The results show that lithium atom doping is a gap doping rather than a substitution doping,and the tetrahedral center(Td)site is the most stable intercalation site.From the analysis of the band structure,it can be seen that the bulk silicon material exhibits metallization characteristics with the insertion of lithium atoms,and as the concentration changes,silicon changes from an indirect bandgap semiconductor to a direct bandgap semiconductor.When the concentration reaches 12.5%,the volume expansion rate increases significantly.At present,a method commonly used to improve the comprehensive performance of silicon-based anode materials for lithium ion batteries is to nano-size and composite silicon materials.Therefore,the intercalation process of lithium atoms in silicon nanowires is studied in this paper,and the mechanism of silicon nanometerization to pulverize silicon during lithium intercalation is analyzed.In this paper,first-principles are used to replace the structural changes and electronic performance transitions of different sites of doped and gap-doped silicon nanowires [1 1 1].At the same time,the effect of size on the lithium nanowire insertion process of silicon nanowires is considered.Studies have shown that interstitial doping is the most ideal doping method.Through the analysis of binding energy,energy band,and density of states,we find that there are large differences in binding energy at different interstitial insertion sites on the surface,middle,and core sites.Surface site gap doping is the most ideal insertion site.At the same time,silicon nanowires can store a large number of lithium ions because of their large specific surface area.As the diameter of silicon nanowires increases,their lithium storage capacity increases.This project focuses on the above-mentioned problems.Aiming at the problem of excessive volume expansion during the lithiumimplantation of silicon anode materials,the lithium-implantation performance of silicon-based anode materials is studied.This work is the development and application of large-capacity lithium-ion batteries with silicon anode materials Provide necessary theoretical foundation and technical support for improvement.