An additive for electrochemical energy storages is disclosed, wherein the additive contains at least one silicon- and alkaline earth metal-containing compound V1 which in contact with a fluorine-containing compound V2 in the energy storage forms at least one compound V3 selected from the group consisting of silicon- and fluorine-containing, lithium-free compounds V3a, alkaline earth metal- and fluorine-containing, lithium-free compounds V3b, silicon-, alkaline earth metal- and fluorine-containing, lithium-free compounds V3c and combinations thereof. Also disclosed is an electrochemical energy storage containing the additive.