FIGS. 8A and 8B illustrate a mode in which the side surfaces of the protrusion in the laminate film are inclined.
When the battery is curved, side surface 104 of the protrusion, in which, electrode group 108 is inserted, of laminate film 101 on the upper side in FIG. 8A is likely to receive significant, tensile stress, and wrinkling or cracking is likely to appear.
Therefore, as illustrated in FIG. 5B, side surface 113 of the protrusion, of laminate film 101 on the upper side is inclined, and thereby it is possible to reduce the tensile stress. A height of side surface 104 of the protrusion in FIG. 8A is the same as a height of side surface 113 of the protrusion in FIG. 8B; however, the side surface is inclined, and thereby a length thereof to the top surface of protrusion 103 can be longer. Since as an allowable length, the length equal to or greater than 1.1 times the height is appropriate, it is desirable that inclined angle D of side surface 113 of the protrusion is equal to or less than 60°. In this manner, side surface 113 of the protrusion is inclined, and thereby it is possible to suppress wrinkling or cracking of the side surface of the protrusion at the time of curvature.
Embodiment 7
FIG. 9 illustrates a mode in which a wave shape is formed in the side surfaces of the protrusion in the laminate film.
