Mg2Si was synthesized by mechanically activated annealing and evaluated as a negative electrode material. A maximum discharge capacity of 830mAh/g was observed by cycling over a wide voltage window of 5–650mV versus Li, but capacity fade was rapid. Cycling over the range 50–225mV versus Li produced a stable discharge capacity of approximately 100mAh/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.