The invention relates to an electrolyte composition containing (i) at least one aprotic polar organic solvent having a flash point above 80° C. and a dielectric constant above 10 at 25° C.; (ii) at least one flame retardant and/or non-flammable solvent; (iii) at least one compound of formula (I) R1—O(O)C—(CH2)n—C(O)O—R2 (I) wherein R1 and R2 are independently from each other selected from C1-C6 alkyl and n is 1, 2 or 3; (iv) at least one conducting salt; (v) at least one aprotic organic solvent having a dynamic viscosity below 1 mPa s at 25° C.; and (vi) optionally one or more additives.