“…This can be investigated through electrode engineering by the use of small particles that could sustain strains with less cracks, the synthesis of composites where metals are embedded in either an active or an inactive matrix, − or the preparation of dense substrated films. − A last approach consisting of designing new powdered multielement alloys that could reversibly react with lithium through a displacement or intercalation process recently revealed very appealing results. Indeed, since the report by Thackeray et al of the insertion of Li into the η-Cu 6 Sn 5 metallic framework, many groups randomly investigated the properties of various binary and even ternary systems. − Among them, the Li−Mg−X systems (X = Si, Ge, Sn, Pb) were recently screened and led to conflicting reports on the reaction proposed to describe the electrochemical lithiation of the structurally alike cubic Mg 2 X phases. − Although the formation of Li 2 MgX phases (Mg 2 X + 2Li → Li 2 MgX + Mg) is a well established and common fact, many questions still remain: the way this ternary phase is formed, its electrochemical activity and stability, the decomposition of the electrodes into Li−X alloys, the formation of Li−Mg phases, the high-voltage behaviors, etc. Among the four Li−Mg−X systems, Li−Mg−Si is the one reaching some kind of consensus, even though the question of the possible formation of Li−Si alloys remains unanswered.…”