NOVELTY - The electric storage device e.g. lithium-ion secondary battery cell (A) has a metal material (13) that is provided with an opposing face that is opposed to a protrusion portion (7A,8A). The metal material joins the protrusion portion by interposing the protrusion portion between a contact portion (3A) of a current collector (2,3) and the metal material. An end region among end regions of opposing face of metal material in one direction along opposing face is displaced in a direction away from contact portion of current collector than a central region of opposing face.    USE - Electric storage device such as lithium-ion secondary battery cell and non-aqueous electrolyte secondary battery cell mounted on running vehicle such as automobile. Can also be used as primary battery cells, and capacitors such as electric double layer capacitor.    ADVANTAGE - The electric storage device can prevent the occurrence of unfavorable conditions such as cracking or tearing in a protrusion portion of an electrode assembly when jointing a current collector to the protrusion portion of the electrode assembly. The stress concentration due to a rapid change in the thickness of the protrusion portion can be mitigated or eliminated so that unfavorable conditions such as cracking or tearing which occur in the protrusion portion caused by pressurization during welding, can be suppressed or avoided, and ultrasonic welding is well performed. Thus it becomes possible to disperse, suppress or eliminate the stress concentration, which is apt to act on the protrusion portion, due to pressure and vibration associated with welding. The lithium-ion secondary battery cell is provided with long life and a high reliability, and is made suitable for a running vehicle as well.    DESCRIPTION OF DRAWING(S) - The drawing shows the partially broken-away front view illustrating the lithium-ion secondary battery cell.    Current collector (2,3)    Contact portion (3A)    Protrusion portion (7A,8A)    Metal material (13)    Lithium-ion secondary battery cell (A)