Energetics of compounds related to Mg2Si as an anode material for lithium-ion batteries using first principle calculations

Electronic energy calculations of (1) Li-intercalated Mg2Si assuming 4b sites occupancy by Li and (2) the formation of MgSiLi2 with the assumed structures by Wengert et al. and Herbst and Meyer have been performed by a density-functional theory. The calculated energy changes for intercalation reactions of Mg8Si4 + nLi → Mg8Si4Lin are +0.349 eV, +0.822 eV, +1.178 eV, and +1.741 eV for n = 1–4, respectively, and the energy change for Mg8Si4 + 8Li → Mg4Si4Li8 + 4Mg is −1.95 eV when Mg is in the metallic state, while +4.12 eV when Mg is in the state of an isolated atom. If we can retard the growth of metallic Mg from Mg2Si by some methods, undesirable structural change of the Mg2Si into MgSiLi2 during charge–discharge cycles would be prevented and intercalation/disintercalation reaction of Li into/from Mg2SiLin (n = 0–1.0) would proceed reversibly by applied electric field.

► The calculated energy changes for Mg8Si4 + nLi → Mg8Si4Lin are +0.349 eV, +0.822 eV, +1.178 eV, and +1.741 eV for n = 1–4, respectively.
► Calculated energy change for Mg8Si4 + 8Li → Mg4Si4Li8 + 4Mg suggested that undesirable structural change from Mg2Si to MgSiLi2 would be prevented if crystal growth of metallic Mg could be retarded.