Exterior material for electricity storage device

A packaging material for a power storage device, comprising at least:

• a substrate layer;
• a metallic foil layer with an anti-corrosion treatment layer being disposed on one face or both faces thereof;
• and
• a sealant layer
• in this order, wherein
• the sealant layer includes a polypropylene-based resin (A) and incompatible component (B) incompatible with the polypropylene-based resin,
• the content of the incompatible component (B) is 1 to 40% by mass based on the total amount of the sealant layer, and
• with regard to an adhered portion resulting from adhesion by heat-sealing the packaging materials stacked so that the sealant layers are opposed to each other under conditions of a temperature of 190° C. and a pressure of 0.5 MPa for 3 seconds, in a graph showing a relationship between a displacement starting at one end and seal strength obtained when the seal strength is continuously measured from the one end to the other end of the adhered portion,
• a maximum seal strength SM is 35 N/15 mm or more, and in addition, the packaging material for a power storage device satisfies the following requirements (1) or (2):
• (1) a stable range of the seal strength is present subsequently to a displacement resulting in the maximum seal strength SM, and a ratio SS/SM of seal strength SS in the stable range to the maximum seal strength SM is 0.3 or more;
• (2) the stable range is not present, and a ratio SA/SM of average seal strength SA from the displacement resulting in the maximum seal strength SM to a displacement ending at the other end to the maximum seal strength SM is 0.3 or more.