NOVELTY - Electrolyte comprises a lithium salt, a non-aqueous organic solvent, and an additive containing substituted phenyl compounds (I).    USE - The electrolyte is useful for lithium secondary battery (claimed).    ADVANTAGE - The electrolyte: is utilized for lithium secondary batteries which improves high temperature lifetime characteristics and high temperature conservation characteristics of the batteries; and improves mobility of lithium ions.    DETAILED DESCRIPTION - Electrolyte comprises a lithium salt, a non-aqueous organic solvent, and an additive containing substituted phenyl compounds of formula (I).    CY1 = aromatic heterocyclic ring or ring connected 4-6C non-aromatic heterocyclic ring; either    R1-R7 = 1-20C alkyl, 1-20C alkoxy, 2-20C alkenyl, 2-20C alkynyl, 2-20C alkylene oxide, 3-30C cycloalkyl, 6-30C aryl, 6-30C aryloxy or 6-30C heteroaryl (all optionally substituted), H, CN, -OR, -C(=O)R1a, -C(=O)OR1a, -OCO(OR1a), -(X)n-NH2, -C=N(R1a), -SR1a, -S(=O)R1a and/or S(=O)2R1a; or at least one of    R1-R7 = polar functional group consisting of CN, -OR, -C(=O)R1a, - C(=O)OR1a, -OCO(OR1a), -(X)n-NH2, -C=N(R1a), -SR1a, -S(=O)R1a or -S(=O)2R1a;    R1a = H, 1-10C alkyl or 6-20C aryl;    R = 1-10C alkyl or 6-20C aryl;    X = 1-10C alkyl or 1-10C alkoxy; and    n = 0-10.    An INDEPENDENT CLAIM is also included for a lithium secondary battery (100), comprising a positive electrode (114) with a positive active material into or from which lithium ions are intercalated or deintercalated, a negative electrode (112) with a negative active material into or from which lithium ions are intercalated or deintercalated and the electrolyte interposed between the positive electrode and the negative electrode.    DESCRIPTION OF DRAWING(S) - The figure shows schematic diagram illustrating perspective view of the lithium secondary battery.    Lithium secondary battery (100)    Negative electrode (112)    Separator (113)    Positive electrode (114)    Battery container (120)