Sealing plate

A sealing plate, comprising:

• an explosion-proof valve that is formed on a part of a plate serving as an outer shell of a container of a sealed battery, and that is opened by a pressure rise in the container, wherein
• the explosion-proof valve comprises:
• a thin plate portion that is formed in a part of the plate and that is thinner than the plate,
• a valve portion that is formed by partially projecting the thin plate portion in a thickness direction to enhance a bending rigidity, and
• a groove that is drawn as a boundary between the valve portion and the thin plate portion to serve as a score line,
• the groove does not enclose the valve portion completely and both end portions of the groove are isolated away from each other,
• the end portions are aligned with a straight line passing through the valve portion,
• the sealing plate further comprises:
• a folding line that extends outside the valve portion in a substantially parallel direction to the straight line on an opposite side of the straight line with respect to a center of the groove, and
• a rupturable portion between the straight line passing through the end portions of the groove and the folding line that is ruptured after the groove is ruptured,
• the valve portion is bent along the folding line to open the explosion-proof valve when the rupturable portion is ruptured after the groove is ruptured, and
• a second length N is a distance between the straight line and the folding line, the second length N being greater than 1 mm.