Mechanism of Lithium Insertion into Magnesium Silicide

The reaction mechanism for electrochemical lithium insertion into magnesium silicide was studies by in situ and ex situ X-ray diffraction (XRD). Lithium intercalation during the initial stages of insertion was indicated by a slight shift toward lower angles in the diffraction patterns. Upon further insertion, Li₂MgSi was formed. This was indicated by the appearance of magnesium peaks, the disappearance of Mg₂Si peaks, and the appearance of Li₂MgSi peaks in the diffraction patterns. Magnesium XRD peaks that accumulated during cycling indicated that the formation of Mg₂Si during lithium removal was not entirely reversible. Li₂MgSi was synthesized by mechanical alloying. XRD patterns and nuclear magnetic resonance spectra of the mechanically alloyed and electrochemically produced phases are compared.