Electric storage cell, covering film and electric storage module

A electric storage cell, having:

• an electric storage element;
• and;
• a covering film package that houses the electric storage element and comprises a covering film having an upper portion and a lower portion which have a seal area where the upper and lower portions of the covering film are sealed around a periphery of the electric storage element to accommodate the electric storage element therebetween, said covering film comprising:
• a metal layer having a first principle face on an electric storage element side and a second principle face on an opposite side of the first principle face,
• an internal resin layer made of synthetic resin and laminated to the first principle face, wherein the internal resin layers of the upper and lower portions are in contact with each other in a contact area including the seal area around the periphery of the electric storage element, and
• an external resin layer made of synthetic resin and laminated to the second principle face, with a slit formed at least in the external resin layer at a location between the seal area and the electric storage element as viewed from above,
• wherein a stress mitigation part to mitigate any stress that tries to separate the internal resin layers that are contacting each other in the contact area, and a stress concentration part where the stress concentrates, are provided between the slit and the electric storage element as viewed from above.