In comparison, when the downward curvature is performed as illustrated in (C) of FIG. 11, compressive stress acts on the wave shape formed on the top surface of the protrusion and the wave shrinks. As a result, the battery is curved without wrinkling. However, when height H of protrusion 103 is significant, the degree of extending of the wave in the case of the upward curvature or a degree of shrinking of the wave in the case of the downward curvature is greater such that it is not possible to cope with the extending or shrinking of the wave, and wrinkling is likely to appear.

As illustrated in (A) of FIG. 12, protrusion 115 is set in laminate film 101 on the upper side and protrusion 116 is formed in laminate film 102 on the lower side. Since the protrusions are set in laminate films on the upper and lower sides, it is possible to set a height of the protrusion to be a half (H/2) the height, respectively, with respect to height H illustrated in (A) of FIG. 11.

In this state, when downward curvature is performed as illustrated in (B) of FIG. 12, the wave formed on protrusion 115 of laminate film 101 on the upper side extends and the wave formed on protrusion 116 of laminate film 102 on the lower side is compressed.

In comparison, when upward curvature is performed as illustrated in (C) of FIG. 12, inversely, the wave formed on protrusion 115 of laminate film 101 on the upper side is compressed, and the wave formed on protrusion 116 of laminate film 102 on the lower side extends.