A high energy density lithium secondary battery comprising: a cathode comprising, as cathode active materials, a first cathode active material represented by Formula 1 below and having a layered structure and a second cathode active material represented by Formula 2 below and having a spinel structure, wherein an amount of the first cathode active material is between 40 and 100 wt% based on a total weight of the first and second cathode active materials, an anode comprising crystalline graphite and amorphous carbon as anode active materials, wherein an amount of the crystalline graphite is between 40 and 100 wt% based on a total weight of the anode active materials; and a separator: Li x (Ni v Mn w Co y M z)O 2-t A t wherein 0.8 < x≤1.3, 0≤v≤0.9, 0≤w≤0.9, 0≤y≤0.9, 0≤z≤0.9, x+v+w+y+z=2, and 0≤t < 0.2; M refers to at least one metal or transition metal cation having an oxidation number of +2 to +4; and A is a monovalent or divalent anion, Li a Mn 2-b M' b O 4-c A' c wherein 0.8 < a≤1.3, 0≤b≤0.5, and 0≤c≤0.3; M' refers to at least one metal or transition metal cation having an oxidation number of +2 to +4; and A' is a monovalent or divalent anion, characterized in that the first cathode active material has an average particle diameter with respect to capacity of 0.03 to 0.1 μm/mAh and has a powder conductivity of 1x10 -3 S/cm or greater to less than 10x10 -3 S/cm at a powder density of 2.65 to 2.85 g/cc; the amorphous carbon is one selected from the group consisting of a first carbon having a specific surface area with respect to capacity of 0.01 to 0.031 m 2 /mAh and a second carbon having a specific surface area with respect to capacity of 0.0035 to 0.0170 m 2 /mAh or a mixture thereof, wherein the first carbon has a powder conductivity of 15 S/cm or greater to less than 100 S/cm at a powder density of 1.0 to 1.2 g/cc, and the second carbon has a powder conductivity of 30 S/cm or greater to less than 100 S/cm at a powder density of 1.4 to 1.6 g/cc;. a cathode comprising, as cathode active materials, a first cathode active material represented by Formula 1 below and having a layered structure and a second cathode active material represented by Formula 2 below and having a spinel structure, wherein an amount of the first cathode active material is between 40 and 100 wt% based on a total weight of the first and second cathode active materials, an anode comprising crystalline graphite and amorphous carbon as anode active materials, wherein an amount of the crystalline graphite is between 40 and 100 wt% based on a total weight of the anode active materials; and a separator: Li x (Ni v Mn w Co y M z)O 2-t A t wherein 0.8 < x≤1.3, 0≤v≤0.9, 0≤w≤0.9, 0≤y≤0.9, 0≤z≤0.9, x+v+w+y+z=2, and 0≤t < 0.2; M refers to at least one metal or transition metal cation having an oxidation number of +2 to +4; and A is a monovalent or divalent anion, Li a Mn 2-b M' b O 4-c A' c wherein 0.8 < a≤1.3, 0≤b≤0.5, and 0≤c≤0.3; M' refers to at least one metal or transition metal cation having an oxidation number of +2 to +4; and A' is a monovalent or divalent anion, wherein 0.8 < x≤1.3, 0≤v≤0.9, 0≤w≤0.9, 0≤y≤0.9, 0≤z≤0.9, x+v+w+y+z=2, and 0≤t < 0.2; M refers to at least one metal or transition metal cation having an oxidation number of +2 to +4; and A is a monovalent or divalent anion, Li a Mn 2-b M' b O 4-c A' c wherein 0.8 < a≤1.3, 0≤b≤0.5, and 0≤c≤0.3; M' refers to at least one metal or transition metal cation having an oxidation number of +2 to +4; and A' is a monovalent or divalent anion, wherein 0.8 < a≤1.3, 0≤b≤0.5, and 0≤c≤0.3; M' refers to at least one metal or transition metal cation having an oxidation number of +2 to +4; and A' is a monovalent or divalent anion, characterized in that the first cathode active material has an average particle diameter with respect to capacity of 0.03 to 0.1 μm/mAh and has a powder conductivity of 1x10 -3 S/cm or greater to less than 10x10 -3 S/cm at a powder density of 2.65 to 2.85 g/cc; the amorphous carbon is one selected from the group consisting of a first carbon having a specific surface area with respect to capacity of 0.01 to 0.031 m 2 /mAh and a second carbon having a specific surface area with respect to capacity of 0.0035 to 0.0170 m 2 /mAh or a mixture thereof, wherein the first carbon has a powder conductivity of 15 S/cm or greater to less than 100 S/cm at a powder density of 1.0 to 1.2 g/cc, and the second carbon has a powder conductivity of 30 S/cm or greater to less than 100 S/cm at a powder density of 1.4 to 1.6 g/cc;.