A new series of electrolyte additives based on simple alkaline earth or related salts has been seen to stabilize the surface of a silicon anode in a lithium-ion cell.   The enhancement in cycling efficiency, cycle life, and stability can be attributed to in-situ formation of a ternary Zintl phase, Li14-xMgxSi4, at the interface, significantly reducing the reactivity with the electrolyte solvents and salts.