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, in which 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; an anode comprising crystalline graphite having a specific surface area with respect to capacity of 0.005 to 0.013 m 2 /mAh as an anode active material, wherein the the crystalline graphite comprises a first crystalline graphite having a specific surface area with respect to capacity of 0.007 to 0.011 m 2 /mAh and has a powder conductivity of 100 S/cm or greater to less than 1000 S/cm at a powder density of 1.4 to 1.6 g/cc, is a surface-modified graphite and has 3R and 2H peaks distinguishable as a rhombohedral peak of a plane at 2θ=43° based on XRD data, 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. 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, in which 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; an anode comprising crystalline graphite having a specific surface area with respect to capacity of 0.005 to 0.013 m 2 /mAh as an anode active material, wherein the the crystalline graphite comprises a first crystalline graphite having a specific surface area with respect to capacity of 0.007 to 0.011 m 2 /mAh and has a powder conductivity of 100 S/cm or greater to less than 1000 S/cm at a powder density of 1.4 to 1.6 g/cc, is a surface-modified graphite and has 3R and 2H peaks distinguishable as a rhombohedral peak of a plane at 2θ=43° based on XRD data, 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, 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.