Magnesium silicide as a negative electrode material for lithium-ion batteries

Mg₂Si was synthesized by mechanically activated annealing and evaluated as a negative electrode material. A maximum discharge capacity of 830 mAh/g was observed by cycling over a wide voltage window of 5–650 mV versus Li, but capacity fade was rapid. Cycling over the range 50–225 mV versus Li produced a stable discharge capacity of approximately 100 mAh/g. X-ray diffraction (XRD) experiments showed that lithium insertion converts Mg₂Si into Li₂MgSi after lithium intercalation into Mg₂Si. Electrochemical evidence of Li–Si reactions indicated that the Li₂MgSi structure can be converted to binary lithium alloys with extensive charging.