The present invention relates to a lithium secondary battery containing an electrolyte consisting of a non-aqueous solvent, a lithium salt and a cathode which comprises 20-100 wt. % lithium transition metal oxide expressed as chemical formula (Li1+zNibMncMe1-(b+c)O2), as the active cathode material. The above electrolyte includes a first additive for forming a protective film (SEI film, or Solid Electrolyte Interface) on the surface of the active anode material, as well as a second additive for forming an SEI film on the surface of the active anode material, while rendering inactive any impurities present on the active cathode material.