The present invention provides a non-aqueous electrolyte comprising: a non-aqueous organic solvent; an imide-based lithium salt; and, as an electrolyte additive, at least one additive selected from the group consisting of lithium difluorooxalate phosphate (LiDFOP), trimethylsilylpropyl phosphate (TMSPa), 1,3-propenesultone (PRS), and ethylene sulfate (Esa). The electrolyte additive for a lithium secondary battery of the present invention can suppress the PF6- decomposition of a positive electrode surface, which may occur at the time of high-temperature cycle operation of a lithium secondary battery, and prevent an oxidation reaction of an electrolyte, thereby improving output characteristics at high and low temperatures and suppressing a swelling phenomenon.