A lithium secondary battery comprising: an electrolyte; an electrode laminate; a battery case (200, 20) comprising a space part in which the electrolyte and the electrode laminate are embedded, and a sealing part surrounding the space part; a gas permeable membrane; and at least one lithium transition metal oxide selected of a compound represented by Formula below and a compound represented by Formula below as a positive electrode active material: Li x M y Mn 2-y O 4-z A z wherein 0.9 ≤ x ≤ 1.2, 0 < y < 2 and 0<z< 0.2; M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti and Bi; A is at least one monovalent or divalent anion, (1-x)LiM'O 2-y A y ·xLi 2 MnO 3-y' A y' wherein M' is Mn a M b; M is at least one selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and Period II transition metals; A is at least one selected from the group consisting of the anions PO 4, BO 3, CO 3 and NO 3; 0<x<1;0<y≤0.02;0<y'≤0.02; 0.5≤a≤1.0;0≤b≤0.5; and a + b = 1; wherein the gas permeable membrane is installed in the space part and between the electrode laminate and the sealing part and through which the electrolyte cannot penetrate, wherein the gas permeable membrane is a selective gas permeable membrane through which oxygen and carbon dioxide are selectively permeated, wherein the gas permeable membrane divides the space part; wherein the gas permeable membrane penetrates the sealing part; and wherein the battery case (200, 20) comprises a first case and a second case sealing the battery case (200, 20) by binding to the first case, and the gas permeable membrane is interposed on an interface between the first case and the second case. an electrolyte; an electrode laminate; a battery case (200, 20) comprising a space part in which the electrolyte and the electrode laminate are embedded, and a sealing part surrounding the space part; a gas permeable membrane; and at least one lithium transition metal oxide selected of a compound represented by Formula below and a compound represented by Formula below as a positive electrode active material: Li x M y Mn 2-y O 4-z A z wherein 0.9 ≤ x ≤ 1.2, 0 < y < 2 and 0<z< 0.2; M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti and Bi; A is at least one monovalent or divalent anion, (1-x)LiM'O 2-y A y ·xLi 2 MnO 3-y' A y' wherein M' is Mn a M b; M is at least one selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and Period II transition metals; A is at least one selected from the group consisting of the anions PO 4, BO 3, CO 3 and NO 3; 0<x<1;0<y≤0.02;0<y'≤0.02; 0.5≤a≤1.0;0≤b≤0.5; and a + b = 1; wherein 0.9 ≤ x ≤ 1.2, 0 < y < 2 and 0<z< 0.2; M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti and Bi; A is at least one monovalent or divalent anion, (1-x)LiM'O 2-y A y ·xLi 2 MnO 3-y' A y' wherein M' is Mn a M b; M is at least one selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and Period II transition metals; A is at least one selected from the group consisting of the anions PO 4, BO 3, CO 3 and NO 3; 0<x<1;0<y≤0.02;0<y'≤0.02; 0.5≤a≤1.0;0≤b≤0.5; and a + b = 1; wherein M' is Mn a M b; M is at least one selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and Period II transition metals; A is at least one selected from the group consisting of the anions PO 4, BO 3, CO 3 and NO 3; 0<x<1;0<y≤0.02;0<y'≤0.02; 0.5≤a≤1.0;0≤b≤0.5; and a + b = 1; wherein the gas permeable membrane is installed in the space part and between the electrode laminate and the sealing part and through which the electrolyte cannot penetrate, wherein the gas permeable membrane is a selective gas permeable membrane through which oxygen and carbon dioxide are selectively permeated, wherein the gas permeable membrane divides the space part; wherein the gas permeable membrane penetrates the sealing part; and wherein the battery case (200, 20) comprises a first case and a second case sealing the battery case (200, 20) by binding to the first case, and the gas permeable membrane is interposed on an interface between the first case and the second case.