First-principles Calculation Study On The Mechanism Of The Silicon Lithiation

With the wide application of the lithium ion batteries, deep research on the anodematerials of the lithium ion batteries is carried out nowadays. As the traditional anodematerials, although carbon can satisfy the need at present, its specific capacity is toosmall in the process of designing the next generation lithium ion batteries. Silicon，which is the same main group element with carbon, has many advantages. Furthermore, because of its many good properties such as extremely high specific capacity(4200mAh/g), silicon becomes one important candidate as anode materials for nextgeneration lithium ion batteries. Based on the first principle calculations, themechanism of the silicon lithiation is studied in this thesis.1. The geometric and electronic structure of the crystalline silicon have beenstudied by first principles calculations. Silicon is iso-structural with the diamond.Atoms are combined by covalent bond. With the total density of states and theprojected density of states, we obtain that the band gap near the Fermi lever is0.46eV,indicating a semiconductor property. Besides, the s orbital and the p orbital of thesilicon are hybridized.2. The lithium intercalation into pure crystalline silicon is carried out. Thenegative intercalation potential indicates that it is energetically favorable to formSi1Li1alloys. Both the band structure and the charge density contours indicate theinteraction between Li and Si is very weak.3. The lithium intercalation into defective crystalline silicon is simulated. Thecalculation results show vacancy can assist lithium intercalation in crystalline silicon.Besides, the binding energy decline gradually with the increase of the distancebetween lithium and vacancy, and the trapping effect is disappeared when the distanceis larger than4.