Theoretical Study On The Effect Of Interface And Silicon Microstructure On Li Ion Transport In Silicon Anode Materials

Silicon with super high lithium intercalation capacity is regarded as the most promising anode material for next generation Li-ion batteries?LIBs?.Recently,Si anodes have received extensive attention of researches.As we know,ion transport in Si anode materials is a key issue affecting its rate performance.In this thesis,the effect of interface and Si microstructures on Li ion transport in Li-Si alloys is studied by first-principles method.The mechanism of ion transport in Si anode materials is further explored.Herein,we first investigated the transverse migration and longitudinal diffusion properties of Li ions in graphene-Si system.Our calculation results of migration energy barriers show that graphene coating can effectively reduce the transport barrier of Li ion at the interface of C-Si composite system,thus promoting the transverse transport of Li ion.The results of diffusion coefficients indicate that graphene coating increases the longitudinal diffusion coefficient of Li ions,which makes Li ions more likely to diffuse into Si materials.Li ion transport is not only affected by the coating of exterior materials,but also closely related to the internal microstructures.Therefore,the effect of Si microstructure on Li ion diffusion is further studied.Two kinds of amorphous Li-Si alloys LiSi and Li₂Si with different Li intercalation concentration were selected.The number of Si microstructures,such as rings,small clusters and chains,was counted.The relationship between the Si microstructures and the Li diffusion coefficients was established.Our results demonstrate that the smaller the number of silicon microstructures are,the greater the degree of Si atom aggregation is,thus the higher the diffusion coefficients of Li ions are.Conversely,small degree of Si atom aggregation results in the lower diffusion coefficients.