A battery cell configured to have a structure in which an electrode assembly is mounted in a battery case made of a laminate sheet comprising a resin layer and a metal layer, and the battery case is provided with an outer edge sealed portion (204, 205), which is formed at an outer edge of a receiving part, in which the electrode assembly is mounted, by thermal welding in order to seal the battery case, two or more sealed lines are formed in two of side sealed portions (202, 203), which are adjacent to the upper sealed portion and the lower sealed portion respectively, such that the sealed lines are spaced apart from each other and parallel to each other, and the sealed lines are continuously formed from an outer edge end of an upper sealed portion to an outer edge end of the lower sealed portion in a longitudinal direction of the battery case, characterised in that: electrode terminals (210, 220) are located at the upper sealed portion and a lower sealed portion, thermally welded portions, which define the sealed lines, and one or more low welded portions are alternately arranged, and in that the outer edge sealed portions (204, 205), in which the sealed lines are formed, are bent between the sealed lines at an angle of 30 to 180 degrees, in that the low welded portions, having a lower thermally welded extent than the thermally welded portions, are located between the thermally welded portions, wherein a thermal welding temperature applied to the thermally welded portions is higher than a thermal welding temperature applied to the low welded portions, and the thickness of the thermally welded portions is relatively small when viewed in vertical section of the outer edge of the sealed portion, whereas the thickness of the low welded portions, which are located between the respective thermally welded portions, is relatively large when viewed in vertical section of the outer edge of the sealed portion. two or more sealed lines are formed in two of side sealed portions (202, 203), which are adjacent to the upper sealed portion and the lower sealed portion respectively, such that the sealed lines are spaced apart from each other and parallel to each other, and the sealed lines are continuously formed from an outer edge end of an upper sealed portion to an outer edge end of the lower sealed portion in a longitudinal direction of the battery case, characterised in that: electrode terminals (210, 220) are located at the upper sealed portion and a lower sealed portion, thermally welded portions, which define the sealed lines, and one or more low welded portions are alternately arranged, and in that the outer edge sealed portions (204, 205), in which the sealed lines are formed, are bent between the sealed lines at an angle of 30 to 180 degrees, in that the low welded portions, having a lower thermally welded extent than the thermally welded portions, are located between the thermally welded portions, wherein a thermal welding temperature applied to the thermally welded portions is higher than a thermal welding temperature applied to the low welded portions, and the thickness of the thermally welded portions is relatively small when viewed in vertical section of the outer edge of the sealed portion, whereas the thickness of the low welded portions, which are located between the respective thermally welded portions, is relatively large when viewed in vertical section of the outer edge of the sealed portion. electrode terminals (210, 220) are located at the upper sealed portion and a lower sealed portion, thermally welded portions, which define the sealed lines, and one or more low welded portions are alternately arranged, and in that the outer edge sealed portions (204, 205), in which the sealed lines are formed, are bent between the sealed lines at an angle of 30 to 180 degrees, in that the low welded portions, having a lower thermally welded extent than the thermally welded portions, are located between the thermally welded portions, wherein a thermal welding temperature applied to the thermally welded portions is higher than a thermal welding temperature applied to the low welded portions, and the thickness of the thermally welded portions is relatively small when viewed in vertical section of the outer edge of the sealed portion, whereas the thickness of the low welded portions, which are located between the respective thermally welded portions, is relatively large when viewed in vertical section of the outer edge of the sealed portion.