A battery cell (200; 300) comprising: an electrode assembly including an electrode tab (221, 222) protruding toward at least one outer periphery; a battery case including an accommodation part in which the electrode assembly is mounted; and an electrode lead (231, 232) connected to the electrode tab for electrical connection with an external device, wherein the electrode lead (231, 232) includes: a tab connection part (231a, 232a) electrically connected to the electrode tab; and a protrusion extension part (231b, 232b) extended from the tab connection part (231a, 232a) and protruding outwardly of the battery case to thereby be electrically connected to the external device, the tab connection part being coated with a gas adsorbent, and wherein the tab connection part is formed to have a length at which both end portions thereof in a width direction perpendicular to a protrusion direction of the electrode tab reach thermally bonded outer peripheries (212b, 212d) of both side surfaces of the battery case, respectively, an insulating film (242, 243) is interposed between both end portions of the tab connection part and the thermally bonded outer peripheries (212b, 212d) of both side surfaces of the battery case so as to improve a sealing property at the time of thermal bonding. an electrode assembly including an electrode tab (221, 222) protruding toward at least one outer periphery; a battery case including an accommodation part in which the electrode assembly is mounted; and an electrode lead (231, 232) connected to the electrode tab for electrical connection with an external device, wherein the electrode lead (231, 232) includes: a tab connection part (231a, 232a) electrically connected to the electrode tab; and a protrusion extension part (231b, 232b) extended from the tab connection part (231a, 232a) and protruding outwardly of the battery case to thereby be electrically connected to the external device, the tab connection part being coated with a gas adsorbent, and wherein the tab connection part is formed to have a length at which both end portions thereof in a width direction perpendicular to a protrusion direction of the electrode tab reach thermally bonded outer peripheries (212b, 212d) of both side surfaces of the battery case, respectively, an insulating film (242, 243) is interposed between both end portions of the tab connection part and the thermally bonded outer peripheries (212b, 212d) of both side surfaces of the battery case so as to improve a sealing property at the time of thermal bonding. a tab connection part (231a, 232a) electrically connected to the electrode tab; and a protrusion extension part (231b, 232b) extended from the tab connection part (231a, 232a) and protruding outwardly of the battery case to thereby be electrically connected to the external device, the tab connection part being coated with a gas adsorbent, and wherein the tab connection part is formed to have a length at which both end portions thereof in a width direction perpendicular to a protrusion direction of the electrode tab reach thermally bonded outer peripheries (212b, 212d) of both side surfaces of the battery case, respectively, an insulating film (242, 243) is interposed between both end portions of the tab connection part and the thermally bonded outer peripheries (212b, 212d) of both side surfaces of the battery case so as to improve a sealing property at the time of thermal bonding.