The invention relates to an additive for electrochemical energy stores, wherein the additive contains at least one compound V1 containing silicon and alkaline earth metal which, in contact with a fluorine-containing compound V2 in the energy store, forms at least one compound V3, the compound V3 being selected from the group of: lithium-free compounds V3a containing silicon and fluorine; lithium-free compounds V3b containing alkaline earth metal and fluorine; and lithium-free compounds V3c containing silicon, alkaline earth metal and fluorine, or combinations thereof. The invention further relates to an electrochemical energy store containing the additive according to the invention.