The geometric and electronic structure of Li15Si4 is studied as the full-lithiated phase of Si anode by first principle calculations within the framework of the density functional theory. The results reveal that the volume change of Si host after Li-intercalation is 269.3%. Besides, the Si host shows metallic properties with the Fermi level crossing the partial-occupied bands after Li intercalation and the chemical bands of Li–Si are found to be polar covalence with some ionicity caused by the partial electron transfer from Li to Si atoms. Further, the deterioration factor of Si anode is analyzed theoretically to be the flaking of active Si off the current collector, which is in agreement with the experimental knowledge. The average intercalation voltage is also calculated to be 0.304V which is close to the experimental value 0.1–0.2V. Moreover, the results demonstrate that the theoretical quantum computations could be a meaningful tool in the research field of Si-based anode.