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 → Mg₈Si₄Li_n 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 Mg₂SiLi_n (n = 0-1.0) would proceed reversibly by applied electric field.